Tag Archives: Physiology

Scarring to the collagen framework causes dysfunction in Duchenne muscular dystrophy

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Muscles that ache after a hard workout usually don’t hurt for long, thanks to stem cells that rush to the injured site along “collagen highways” within the muscle and repair the damaged tissue. But if the cells can’t reach their destination, the damaged tissue can’t regenerate. Over time, it breaks down completely and ceases to function.

In a study recently published in npj Regenerative Medicine, a group of researchers led by biochemists at UCLA show for the first time that scarring to the collagen framework that carries these healing cells causes muscles to gradually stop working in Duchenne muscular dystrophy. The discovery in mice illuminates one reason stem cell therapy has not been effective for the disorder: The cells simply can’t get where they’re needed most.

Duchenne muscular dystrophy is the most common -; and one of the most severe -; hereditary muscular dystrophies. The muscle-wasting disease, which usually affects boys, begins in childhood and inevitably ends in death as the muscles that power the heart, lungs and other vital organs fail. It is caused by a mutation in the gene for the dystrophin protein, which regulates the organization of muscle cells. In healthy people, dystrophin helps bundles of muscle cells called myofibers attach to the collagen framework -; the extracellular matrix that gives muscles their shape, holds them together and provides the “highway” for stem cells to repair and regenerate damaged tissue.

Rachelle Crosbie, a UCLA professor of integrative biology and physiology who is looking for ways to treat Duchenne muscular dystrophy, suspected that the dysfunction caused by this mutation led to scarring and stiffening of the extracellular matrix, a process known as fibrosis.

Crosbie and Kristen Stearns-Reider, a postdoctoral fellow in Crosbie’s laboratory, designed a unique experiment to find out. Using facilities at UCLA’s California NanoSystems Institute, they devised a process to “wash” all the cells off the collagen extracellular matrix in healthy mice and those with Duchenne muscular dystrophy.

Under a microscope, the two cell-free matrices, which Crosbie calls “myoscaffolds,” appeared very different: The healthy one looked like delicate lace, while the Duchenne one looked more like a dense sponge.

Next, the researchers seeded each myoscaffold with stem cells and watched as the cells tried to grow muscle tissue. Muscle stem cells grew on the myoscaffolds exactly as they would in healthy and diseased muscle: In the healthy, lacy myoscaffold, cells migrated along the smooth threads and deposited themselves in evenly spaced holes. However, the bumpy, thickened surfaces of the Duchenne myoscaffold made travel difficult and threw up roadblocks that caused the cells to pile up in clumps; the cells were stressed an unable to progress efficiently.

Like suburban commuters, resident stem cells live on outskirts of the muscle fiber and travel along the muscle fiber to damaged areas and regenerate muscle. The extracellular matrix is the highway they use. It’s like the difference between driving to work on a regular day versus the day a landslide fell on the freeway.”

Rachelle Crosbie, UCLA professor of integrative biology and physiology

This is the first time scientists have imaged living cells in a fibrotic myoscaffold, revealing specifically how fibrosis disrupts cell behavior, Crosbie said.

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The thin, supple threads of the healthy scaffold also yielded slightly as stem cells attached to them, a deformation critical to the successful development of muscle tissue. The stem cells were unable to deform the thick, stiff fibers of the Duchenne scaffold. Tissue grown on the Duchenne scaffold showed large clumps of myofibers interspersed with even larger clumps of collagen instead of the evenly distributed myofibers seen in the healthy sample.

Protein sarcospan offers a potential way forward

The research team then tested cell behavior on a Duchenne myoscaffold that was created using a therapeutic protein called sarcospan, which is known to stabilize the extracellular matrix. Stem cell function improved once sarcospan had minimized the formation of fibrotic scars.

“The results made it really clear why stem cell therapies have proven challenging for Duchenne muscular dystrophy,” Crosbie said. “Finding ways to prevent or reduce scarring on the extracellular matrix could make them more effective.”

These myoscaffolds offer several broad possibilities for studying stem cell–extracellular matrix interactions, stem cell niche formation, the microenvironments that influence stem cell behavior, muscle maturation and disease modeling, said study co-authors Michael Hicks, a UCLA postdoctoral fellow, and April Pyle, a UCLA professor of microbiology, immunology, and molecular genetics.

Crosbie also noted that because the new method requires only very small samples, these studies could potentially be extended to include individual patients, using tissue from a muscle biopsy to study treatments before they are administered and identifying ones more likely to be effective.

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Journal reference:

Stearns-Reider, K. M., et al. (2023). Myoscaffolds reveal laminin scarring is detrimental for stem cell function while sarcospan induces compensatory fibrosis. Npj Regenerative Medicine. doi.org/10.1038/s41536-023-00287-2.

Study may provide new avenues for addressing somatosensory symptoms of long COVID

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COVID-19, the disease resulting from SARS-CoV-2 infection, is associated with highly variable clinical outcomes that range from asymptomatic disease to death. For those with milder infections, COVID-19 can produce respiratory infection symptoms (cough, congestion, fever) and sensory phenotypes such as headache and loss of sense of smell. In more severe cases, SARS-CoV-2 infection can affect nearly every organ and result in strokes from vascular occlusion, cardiovascular damage and acute renal failure. A substantial number of actively infected patients suffering from both mild and severe infections experience sensory-related symptoms, such as headache, visceral pain, Guillain-Barre syndrome, nerve pain and inflammation. In most patients these symptoms subside after the infection ends, but, for other patients, they can persist.

In a new study, researchers from Boston University Chobanian & Avedisian School of Medicine, Icahn School of Medicine at Mount Sinai (Icahn Mount Sinai) and New York University (NYU), have found that thousands of genes were affected by SARS-CoV-2-mediated disease even after the viral infection had been cleared. These genes were associated with neurodegeneration and pain-related pathways, suggesting lasting damage to dorsal root ganglia (spinal nerves that carry sensory messages from various receptors) that may underlie symptoms of Post-Covid Conditions also known as Long Covid.

Several studies have found that a high proportion of Long Covid patients suffer from abnormal perception of touch, pressure, temperature, pain or tingling throughout the body. Our work suggests that SARS-CoV-2 might induce lasting pain in a rather unique way, emphasizing the need for therapeutics that target molecular pathways specific to this virus.”

Venetia Zachariou, PhD, corresponding author, chair of pharmacology, physiology & biophysics at BU Chobanian & Avedisian School of Medicine

This work was performed in collaboration with Benjamin tenOever, PhD, professor of microbiology and medicine at NYU, formerly at Icahn Mount Sinai.

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Using an experimental model infected with SARS-CoV-2, the researchers studied the effects of infection on sensitivity to touch, both during active infection and well after the infection had cleared. They then compared the effects of SARS-CoV-2 to those triggered by influenza A virus infection. In the experimental model, they observed a slow but progressive increase in sensory sensitivity over time – one that differed substantially from viral control, influenza A virus, which caused quick hypersensitivity during active infection but returned to normal by the time infection was over.

According to the researchers, this model can be used to gain information on genes and pathways affected by SARS-CoV-2, providing novel information to the scientific community on gene expression changes in sensory ganglia several weeks after infection.

“We hope this study will provide new avenues for addressing somatosensory symptoms of long COVID and ME/CFS (myalgic encephalomyelitis/chronic fatigue syndrome), which are only just now beginning to be addressed by mainstream medicine. While we have begun using this information by validating one promising target in this study, we believe our now publicly available data can yield insights into many new therapeutic strategies,” adds Zachariou.

These findings appear online in the journal Science Signaling.

This study was supported by National Institute of Neurological Disorders and Stroke NS086444S1 (R.A.S), the Zegar Family Foundation (B.T.) and the Friedman Brain Institute Research Scholars Program (V.Z., B.T., R.A.S., J.J.F.).

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Journal reference:

Serafini, R. A., et al. (2023) SARS-CoV-2 airway infection results in the development of somatosensory abnormalities in a hamster model. Science Signaling. doi.org/10.1126/scisignal.ade4984.

Discovery offers a potential target for TB therapies

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In ongoing research aimed at developing more effective treatments for tuberculosis (TB), University of Massachusetts Amherst microbiologists have identified a long-sought gene that plays a critical role in the growth and survival of the TB pathogen.

The discovery offers a potential target for drug therapies for a deadly disease that has few effective treatments and in 2021 alone sickened 10.6 million worldwide and caused 1.6 million deaths, according to the World Health Organization.

Published in the journal mBio, the research showed that the putative gene cfa encodes an essential enzyme directly involved in the first step of forming tuberculostearic acid (TBSA), a unique fatty acid in the cell membranes of mycobacteria. TBSA was first isolated from mycobacteria nearly 100 years ago but exactly how it’s synthesized had remained elusive.

“There is a long history associated with this very fascinating fatty acid,” says senior author Yasu Morita, associate professor of microbiology, in whose lab lead authors Malavika Prithviraj and Takehiro Kado carried out the research.

The experiments revealed how TBSA controls the functions of the mycobacterial plasma membrane, which acts as a protective barrier for the TB pathogen to survive in human hosts for decades.

Cfa is directly involved in the formation of tuberculostearic acid and is also involved in the organization of the plasma membrane, and that all fell in place with our hypothesis.”

Malavika Prithviraj, Lead Author

The focus of research in Morita’s lab is to identify ways to interrupt homeostasis of the thick and waxy cell envelope, which includes the plasma membrane, so the mycobacteria are unable to grow or vulnerable to attack. Prithviraj, a Ph.D. student, and colleagues performed cellular lipidomics to confirm what researchers have suspected for some 60 years.

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“People have been very, very interested in understanding how this lipid is made and what it is doing in the cell,” Morita says. “Malavika figured out that Cfa is the enzyme that makes this lipid, which is such a unique lipid that researchers have been pursuing this lipid as a diagnostic marker for TB.”

In previous experiments, the Morita lab had noted that plasma membrane domains found at polar regions of the cell were important for the growth of the mycobacteria.

“We were interested in understanding how this particular membrane domain is compartmentalized and organized in the bacteria,” Prithviraj says. “We worked with a deletion strain of cfa and also a complement strain wherein we could add it back into the bacteria and check what exactly was its function.”

The TB pathogen usually stays alive but dormant in the body for years or decades, thanks to its protective surface structure. Morita and his team work on a nonpathogenic model organism primarily to figure out what features of bacteria are needed for them to survive and grow.

The researchers found that TBSA also prevents “tight packing” inside the membrane. “If the membrane is too rigid, it cannot function properly, and so the membrane dynamics, or maintaining membrane fluidity, is very important,” Morita says. “What we showed in this paper is that tuberculostearic acid is likely a very important molecular key for maintaining this proper fluidity.”

The findings will help researchers take the next step toward developing new TB treatments.

“We would be interested in understanding the effects of the gene in TB infection and how Cfa might be helping the bacteria to survive in the human host” Prithviraj says. “If we find a way to disrupt the membrane fluidity maintenance, the cells cannot grow efficiently and would eventually die.”

Morita adds, “There are many drugs used for treating TB, but there has been no previous demonstration that this particular aspect of mycobacteria physiology can be used as a direct target,” Morita says. “This study is showing it could be.”

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Journal reference:

Prithviraj, M., et al. (2023) Tuberculostearic Acid Controls Mycobacterial Membrane Compartmentalization. mBio. doi.org/10.1128/mbio.03396-22.

New Research Casts Fundamental Doubt on Long-Established Standard Model of Electroporation

Powerful electric fields have the ability to generate pores in biological membranes through a process called electroporation. Deliberately inducing these imperfections in membranes is a crucial technique not only in medicine and biotechnology but also in the treatment of food items.

A Franco-German research team, headed by Dr. Carlos Marques from the Ecole Normale Supérieure in Lyon, France, and Prof. Dr. Jan Behrends from the Institute of Physiology at the University of Freiburg, has recently collected data that casts fundamental doubt on what has been accepted for decades as the standard model of this mechanism.

“This is a challenge for theory building and numerical simulations in this field,” says Marques. The results have now been published in the Proceedings of the Academy of Sciences of the United States of America (PNAS). They could help to improve the transport of active substances in cells.

Direct current electric fields above a certain intensity disrupt the organization of lipids, fat-like molecules that form the basic structure of biological membranes in a bilayer, stacked together in a kind of liquid crystal. The resulting electropores, which are usually only stable for a very short time, allow water and solutes in the surrounding medium – such as drugs or other active substances, including RNA or DNA – to enter a cell.

Since the bilayer of lipids is very thin, measuring only five-millionths of a millimeter, it is not necessary to apply very high voltages to generate very high field strengths (volts per meter). Thus, even at a voltage of 0.1 volts across the membrane, the field strength is 20 million volts per meter. In air, for example, spark discharge already occurs at three million volts per meter. However, it must be direct current voltage; alternating current fields in the megahertz-gigahertz range such as those generated by cell phones do not cause pores. While the technique is well established, there is still a need to optimize electroporation of cell membranes for various purposes, such as to introduce genetic material for gene therapy. For this purpose, it is important to understand precisely the mechanism of pore formation under electric fields.

A standard theoretical model of electroporation from the 1970s assumes that the electric field applies pressure to the lipids, thereby increasing the probability of pore formation. So far, however, there is only little experimental verification of the model. This is due, first, to the difficulty of directly detecting the formation of electropores and, second, to the necessity of carrying out a very large number of such experiments in order to arrive at statistically tenable conclusions. This is because, in contrast to pores formed by proteins, electropores exhibit a very diverse, less stereotypical behavior.

A method that is capable of detecting the formation of pores with great accuracy and high time resolution is the electrical measurement of ionic current. Ions are positively or negatively charged constituents of the salts present in all biological fluids and, thus, inside and outside the cell. They are practically incapable of penetrating intact membranes, but as soon as a pore is opened, they are transported through it in the electric field. This transport of charged particles can be measured with highly sensitive amplifiers as a tiny electric current of a few billionths to millionths of an ampere. For this purpose, artificial lipid bilayers are created in thin Teflon layers via tiny openings of around 0.1 millimeters in diameter and placed between two electrodes. This technique of membrane formation is highly susceptible to failure – only one membrane is formed at a time, which breaks easily, especially during tests with higher voltages.

For their experiments, the research group used a microchip with many openings, through which significantly more stable lipid layers can be generated very quickly and repeatedly using simplified procedures. This so-called microelectrode cavity array (MECA) was developed by Jan Behrends’s research group and has been produced and made commercially available by the Freiburg start-up company Ionera Technologies GmbH founded in 2014.

With the help of this device, it was now possible for the doctoral candidate Eulalie Lafarge from the Charles Sadron Institute at the University of Strasbourg and Dr. Ekaterina Zaitseva from the Freiburg research group to generate hundreds of membranes in a relatively short time and to measure and quantify pore formation as a function of the strength of the direct current field.

The results demonstrated that, contrary to the prediction of the old standard model, the energy barrier for pore formation decreases not with the square of the field strength but proportionally to the field strength. In other words, doubling the field strength reduces the energy barrier only by half, not fourfold. This suggests a fundamentally different mechanism: a destabilization of the interface between lipid and water due to a reorientation of the water molecules in the electric field.

This result was also confirmed for membranes whose lipids were oxidized to varying degrees. This is interesting because lipid oxidation is a natural process in the regulation of cell membrane function and plays a role in the natural aging of the organism and possibly also in diseases such as Parkinson’s and Alzheimer’s. “Particularly in view of the medical significance of this topic, we want to pursue it further, also including optical methods, in order to reach a real understanding of this important phenomenon,” says Behrends.

Reference: “Activation energy for pore opening in lipid membranes under an electric field” by Eulalie J. Lafarge, Pierre Muller, André P. Schroder, Ekaterina Zaitseva, Jan C. Behrends and Carlos M. Marques, 7 March 2023, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2213112120

New discoveries made regarding autism onset in mouse models

Although autism is a common neurodevelopmental disorder, the multiple factors behind its onset are still not fully understood. Animal models of idiopathic autism, especially mice, are often used to help researchers understand the complicated mechanisms behind the disorder, with BTBR/J being the most commonly used mouse model in the world.

Now, an international research collaboration including Kobe University’s Professor TAKUMI Toru and Researcher Chia-wen Lin et al. have made new discoveries regarding autism onset in mouse models.

In their detailed series of experiments and analyses of BTBR/J mice and the other subspecies BTBR/R, they revealed that endogenous retrovirus activation increases a fetus’s susceptibility to autism. They also discovered that BTBR/R exhibits autistic-like behaviors without reduced learning ability, making it a more accurate model of autism than the widely-used BTBR/J model.

It is hoped that further research will contribute towards better classification of autism types, as well as the creation of new treatment strategies for neurodevelopmental disorders.

These research results were published in Molecular Psychiatry on March 7, 2023

Main points

  • The researchers analyzed BTBR/J, a widely used mouse model of autism, and its subspecies BTBR/Rusing MRI. This revealed that the corpus callosum, which connects the left and right hemispheres of the brain, was impaired in BTBR/J mice but not in BTBR/R mice.
  • Genome and transcription analysis showed that BTBR mice have increased levels of endogenous retrovirus genes.
  • Furthermore, single-cell RNA analysis of BTBR/R mice revealed changes in the expression of various genes (including stress response genes) that are indicative of endogenous retrovirus activation.
  • Even though BTBR/J and BTBR/R mice have the same ancestry, the results of various behavioral analysis experiments revealed differences in spatial learning ability and other behaviors between the two types of model mice.

Research background

Autism (autism spectrum disorder) is a neurodevelopmental disorder that remains largely unexplored despite the rapidly increasing number of patients. Reasons for this continuing increase in people diagnosed with autism include changes to diagnostic criteria and older fathers becoming more common. Autism is strongly related to genetic factors and can be caused by abnormalities in DNA structure, such as copy number variations. Animal models, especially mice, are often used in research to illuminate the pathology of autism. Among these models, BTBR/J is a mouse model of the natural onset of autism that is commonly used. Studies have reported various abnormalities in BTBR/J mice including impairment of the corpus callosum (which connects the left and right hemispheres of the brain) and excessive immune system signaling. However, it is not fully understood why this particular lineage displays autistic-like behavioral abnormalities.

The aim of the current study was to shed light on the onset mechanism of these autistic-like behavioral abnormalities by conducting comparative analysis on BTBR/J and its subspecies BTBR/R.

Research findings

First of all, the researchers conducted MRI scans on BTBR/J and BTBR/R mice to investigate structural differences in each region of the brain. The results revealed that there were differences between BTBR/J and BTBR/R mice in 33 regions including the amygdala. A particularly prominent difference discovered was that even though BTBR/J’s corpus callosum is impaired, BTBR/R’s is normal.

Next, the research group used the array CGH method to compare BTBR/R’s copy number variations with that of a normal mouse model (B6). They revealed that BTBR/R mice had significantly increased levels of endogenous retroviruses (ERV) in comparison to B6 mice. Furthermore, qRT-PCR tests revealed that these retroviruses were activated in BTBR/R mice. On the other hand, in B6 mice there was no change in the expression of LINE ERV (which is classified in the same repetitive sequence), indicating that this retroviral activation is specific to BTBR.

Subsequently, the researchers carried out single-cell RNA analysis on the tissue of embryonic BTBR mice (on the AGM and yolk sac). The results provide evidence of ERV activation in BTBR mice, as expression changes were observed in a group of genes downstream of ERV.

Lastly, the researchers comprehensively investigated the differences between BTBR/J and BTBR/R on a behavioral level. BTBR/R mice were less anxious than BTBR/J and showed qualitative changes in ultrasound vocalizations, which are measured as a way to assess communicative ability in mice. BTBR/R mice also exhibited more self-grooming behaviors and buried more marbles in the marble burying test. These two tests were designed to detect repetitive behavioral abnormalities in autistic individuals. From the results, it was clear that BTBR/R exhibits more repetitive behaviors (i.e. it is more symptomatic) than BTBR/J. The 3-chamber social interaction test, which measures how closely a mouse will approach another mouse, also revealed more pronounced social deficits in BTBR/R than BTBR/J mice (Figure 4i). In addition, a Barnes maze was used to conduct a spatial learning test, in which BTBR/J mice exhibited reduced learning ability compared to B6 (normal mice). BTBR/R mice, on the other hand, exhibited similar ability to B6.

Overall, the study revealed that retrovirus activation causes the copy number variants in BTBR mice to increase, which leads to the differences in behavior and brain structure seen in BTBR/J and BTBR/R mice (Figure 5).

Further developments

BTBR/J mice are widely used by researchers as a mouse model of autism. However, the results of this study highlight the usefulness of the other lineage of BTBR/R mice because they exhibit autistic-like behavior without compromised spatial learning ability. The results also suggest that it may be possible to develop new treatments for autism that suppress ERV activation. Furthermore, it is necessary to classify autism subtypes according to their onset mechanism, which is a vital first step towards opening up new avenues of treatment for autism.

Journal reference:

Lin, C-W., et al. (2023) An old model with new insights: endogenous retroviruses drive the evolvement toward ASD susceptibility and hijack transcription machinery during development. Molecular Psychiatry. doi.org/10.1038/s41380-023-01999-z.

Gut-on-a-chip devices can bridge lab models and human biology

The gut is one of the most complex organs in the body. Inside, it teems with a diverse microbial population that interacts and cooperates with intestinal cells to digest food and drugs. Disruptions in this microbiome have strong links to a wide spectrum of diseases, such as inflammatory bowel disease, obesity, asthma, and even psychological and behavioral disorders.

Valid models of the gut are therefore immensely useful for understanding its function and associated ailments. In APL Bioengineering, by AIP Publishing, researchers from the University of California, Berkeley and Lawrence Berkeley National Lab described how gut-on-a-chip devices can bridge lab models and human biology.

Organ-on-a-chip devices are miniaturized models of human organs. They contain tiny microchannels where cells and tissue cultures interact with precisely controlled nutrients. Regulating the cell’s environment in such a way is crucial for creating realistic models of tissue.

Using these models avoids the time-consuming and costly challenges of clinical trials and the ethical issues behind animal testing.

“Medical research is currently facing major hurdles, both in terms of understanding the basic science governing the function of human organs and the research and development of new drugs and therapeutics,” said author Amin Valiei. “Access to valid models of human organs that can be studied conveniently in the lab can significantly accelerate scientific discoveries and the development of new medications.”

Modeling the microbiome is particularly difficult because of its unique environmental conditions. Through creative design, gut-on-a-chip devices can simulate many of these properties, such as the gut’s anaerobic atmosphere, fluid flow, and pulses of contraction/relaxation. Growing intestinal cells in this environment means that they more closely resemble human biology compared to standard laboratory cell cultures.

“Recent gut-on-a-chip models have demonstrated success in maintaining a viable coculture of the human intestinal cells and the microbiome for a few days and even up to weeks,” said Valiei. “This opens new ways to analyze the microbiome under biologically relevant conditions.”

The authors highlight key gut-on-a-chip devices and their success in simulating microbial and human cellular biology. They also describe current disease models and drug studies using the technology.

“Its unique capabilities make the organ-on-a-chip apt for plenty of research investigations in the future,” said Valiei.

The team is currently investigating dysbiosis, an imbalance in the gut microbial community with major health consequences. They aim to find innovative ways to diagnose, mitigate, and treat this condition.

Rheumatoid arthritis (RA)  is a complex, chronic inflammatory disease that is thought to affect about one percent of …

Rheumatoid arthritis (RA)  is a complex, chronic inflammatory disease that is thought to affect about one percent of the world’s population. RA happens when a person’s own antibodies attack joint tissue, causing painful swelling, stiffness, and redness. Some research has suggested that there is a link between RA and gum disease.

Image credit: Pixabay

Gum disease is estimated to affect up to 47 percent of adults, and in the disorder, oral microbes can move to the blood after the gums start to bleed. An increase in disease activity has been observed in RA patients who also have gum disease. Gum disease has been shown to be more common in RA patients who carry a certain type of antibodies, called anti-citrullinated protein antibodies (ACPAs), though ACPAs are often found in the blood of individuals with RA. The presence of ACPAs can often predate the diagnosis of RA by a few years.

A new study investigated the connections between these observations. In this work, the researchers collected blood samples from a small group of ten people with RA, five with and five without gum disease. These samples were collected every week for one year, and the investigators assessed the expression of both human and bacterial genes in those samples.

Certain types of inflammatory immune cells carried gene expression signatures that were associated with the autoimmune flares of arthritis patients who also had periodontal disease, as well as the presence of certain oral bacteria in the blood.

Many of these oral bacteria were chemically altered by deimination; they were citrullinated. Citrullination can change the structure and function of proteins. Although citrullination can be a part of the normal function of tissues, high levels of citrullination have been linked to inflammation.

Citrullination can also create targets for ACPAs; when the normal, unconverted forms of the oral bacteria were incubated with ACPAs, the antibodies did not react, but when the citrullinated oral bacteria were exposed to ACPAs, there was a reaction. ACPAs appear to be bound to oral microbes in RA patients.

The findings have been reported in Science Translational Medicine.

The study noted that the immune response to oral microbes could be influencing RA flares, that oral microbes can trigger a specific antibody reaction in patients with both RA and gum disease, and that RA flares cause varying immune signatures, which could reflect different flare triggers.

It could be that gum disease repeatedly causes the immune system to respond, and as the immune system keeps reacting and repeatedly increasing inflammation, RA may eventually begin to emerge. More work will be needed, however, to fully understand whether gum disease is playing a causative role in the development of RA.

Source: Science Translational Medicine

Carmen Leitch

Experts Debunk Scientific Claims That Human Babies Are Colonized by Bacteria Before Birth

Leading experts from several scientific disciplines find flaws in studies that suggest the existence of a “fetal microbiome.”

Scientific claims that babies harbor live bacteria while still in the womb are inaccurate, and may have impeded research progress, according to University College Cork (UCC) researchers at APC Microbiome Ireland, a world-leading Science Foundation Ireland (SFI) Research Centre, which led a perspective published today (January 25, 2023) in the prestigious scientific journal Nature.  

Prior claims that the human placenta and amniotic fluid are normally colonized by bacteria would, if true, have serious implications for clinical medicine and pediatrics. It would also undermine established principles in immunology and reproductive biology.

To examine these claims, UCC & APC Principal Investigator Prof. Jens Walter assembled a trans-disciplinary team of 46 leading experts in reproductive biology, microbiome science, and immunology from around the world to evaluate the evidence for microbes in human fetuses.

The team unanimously refuted the concept of a fetal microbiome and concluded that the detection of microbiomes in fetal tissues was due to contamination of samples drawn from the womb. Contamination occurred during vaginal delivery, clinical procedures, or during laboratory analysis.

In the report in Nature, the international experts encourage researchers to focus their studies on the microbiomes of mothers and their newborn infants and on the microbial metabolites crossing the placenta which prepare the fetus for post-natal life in a microbial world.

According to Prof. Walter: “This consensus provides guidance for the field to move forward, to concentrate research efforts where they will be most effective. Knowing that the fetus is in a sterile environment, confirms that colonization by bacteria happens during birth and in early post-natal life, which is where therapeutic research on modulation of the microbiome should be focused.”

The expert international authors also provide guidance on how scientists in the future can avoid pitfalls of contamination in the analysis of other samples where microbes are expected to be absent or present at low levels, such as internal organs and tissues within the human body.  

Reference: “Questioning the fetal microbiome and pitfalls of low-biomass microbial studies” 25 January 2023, Nature.
DOI: 10.1038/s41586-022-05546-8

Gut feelings can be very real. There are neurons that connect the gut directly to the brain, and …

Gut feelings can be very real. There are neurons that connect the gut directly to the brain, and this so-called gut-brain axis has a significant influence on the body.
The microbes in the gut can also affect the brain, and researchers are trying to decipher the complex relationship between the brain and microorganisms in the body. Recent work has shown how microbial metabolites can influence brain function. Neurotransmitters can also affect gut physiology. Now scientists have developed a process that can be used by other researchers to develop a deep understanding of how gut microbes impact the brain. The work has been reported in Nature Protocols.

Image credit: Pixabay

“Currently, it is difficult to determine which microbial species drive specific brain alterations in a living organism,” said first study author, Dr. Thomas D. Horvath, an instructor at Baylor College of Medicine and Texas Children’s Hospital. “Here we present a valuable tool that enables investigations into connections between gut microbes and the brain.”

“Gut microbes can communicate with the brain through several routes, for example by producing metabolites, such as short-chain fatty acids and peptidoglycans; neurotransmitters, such as gamma-aminobutyric acid and histamine; and compounds that modulate the immune system as well as others,” added co-first study author Dr. Melinda A. Engevik, an assistant professor at the Medical University of South Carolina.

Related: Bugs on the Brain – Gut Microbes Affect Neurodegeneration

In this process, the researchers suggest creating a three-stage workflow. First, microbes should be prepared in a defined culture media. Next, intestinal organoids are injected with the microbes.  Finally, animal models are used that have either complete gut microbiomes; germ-free mice that lack microbiomes; mice that began as germ-free but were colonized with gut microbiota that carried no pathogens; and mice that started out germ-free but were colonized with individual strains of a gut microbe – Bifidobacterium dentium or Bacteroides ovatus.

The short-chain fatty acids produced by gut microbes can have a physiological impact on the brain, and they can be isolated and analyzed by  liquid chromatography–tandem mass spectrometry (LC/MS) along with any neurotransmitters that are derived from microbes.

This methodology is different from research that only assesses material in stool samples, because it encompasses many other things including in vivo models and cell cultures. The study authors estimated that the mouse colonization process requires about three weeks and LC/MS techniques take about another two weeks.

“We can expand our study to a community of microbes,” said study co-author Dr. Jennifer K. Spinler, an assistant professor at Baylor and the Texas Children’s Hospital Microbiome Center. “This protocol gives researchers a road map to understand the complex traffic system between the gut and the brain and its effects.”

Sources: Baylor College of Medicine, Nature Protocols

Carmen Leitch

Researchers explore the mechanism involved in the living world’s fastest cell movements

Raphidocystis contractilis belongs to Heliozoa, a group of eukaryotes commonly found in fresh, brackish, and sea water. The organisms of this group have finger-like arms-;axopodia-;which radiate out from their body, giving them a sun-like appearance. Hence, they are also known as “solar worms”. Each axopodium is composed of the proteins, alpha-beta tubulin heterodimers, which form filaments called microtubules. R. contractilis can withdraw its axopodia extremely fast in response to external stimuli. However, the mechanism underlying this rapid arm shortening remains a mystery.

To this end, a team of researchers including Professor Motonori Ando, Dr. Risa Ikeda (both from the Laboratory of Cell Physiology) and Associate Professor Mayuko Hamada (from the Ushimado Marine Institute), of Okayama University, Japan, explored the mechanism involved in one of the fastest cell movements in the living world.

So, where did it all begin? Sharing the motivation behind their study, Professor Ando says, “Recently, a wide variety of heliozoans have been discovered in various hydrospheres in the Okayama Prefecture, making it clear that several species of sun worms inhabit the same environment. We are trying to unravel the mysteries around these protozoans and gradually expand the horizons of our knowledge.”

The authors started their investigation by immunolabelling the tubulin protein and observing its movement before and after axopodial contraction. They found that before shortening, tubulins were arranged systematically all along the length of the axopodia, but after axopodial withdrawal, those swiftly accumulated at the cell surface. This led them to believe that during the rapid axopodial withdrawal, the microtubules broke down into tubulin instantly. However, microtubule degradation is generally not a rapid phenomenon; it progresses rather slowly.

How then, could R. contractilis achieve this change so quickly?

The researchers hypothesized that this was possible if the microtubules split at multiple sites simultaneously. To validate their hypothesis, the authors set out to find the proteins and genes involved in the instant cleavage of microtubules in R. contractilis. Their findings were published online in The Journal of Eukaryotic Microbiology on 21 November 2022.

The researchers performed de novo transcriptome sequencing (analysis of the genes expressed at a particular time in a cell) and identified close to 32,000 genes in R. contractilis. This gene set was most similar to that found in protozoans (which are single-celled organisms), followed by metazoans (multicellular organisms with well-differentiated cells; this includes humans, and other animals).

Homology and phylogenetic analysis of the obtained gene set revealed several genes (and their corresponding proteins) involved in microtubule disruption. Among these, the most important ones were katanin p60, kinesin, and calcium signaling proteins. Katanin p60 was involved in controlling the axopodial arm length. Several duplicates of kinesin genes were found. Among the identified kinesins, kinesin-13, a major microtubule destabilizing protein, was found to play an important role in the rapid contraction of axopodia. Calcium signaling genes regulate the entry of calcium ions into the cell from its surroundings and the induction of axopodial withdrawal.

The researchers also noticed a lack of genes linked with flagellar formation and motility, indicating that the axopodia of R. contractilis have not evolved from flagella. Although many genes remain unclassified, the newly established gene set will serve as a reference for future studies aiming to understand the axopodial motility of R. contractilis.

Heliozoan axopodia can function as a sensitive sensor. They can detect minute changes in their environment, e.g., the presence of heavy metal ions and anticancer drugs. Discussing their vision for the future, Professor Ando shares, “We believe that the axopodial response of heliozoa can be used as an index to develop temporary detection and monitoring devices for environmental and tap water pollution. It can also be used as a novel bioassay system for the primary screening of novel anticancer drugs. In the future, we plan to continue to work together as a team to enhance basic and applied research on these organisms.”

Heliozoans have proved yet again that a single cell has immense potential to change the world. We wish the authors success in turning their vision to reality!

Journal reference:

Ikeda, R., et al. (2022) De novo transcriptome analysis of the centrohelid Raphidocystis contractilis to identify genes involved in microtubule-based motility. Journal of Eukaryotic Microbiology. doi.org/10.1111/jeu.12955.