Comment

Comment by Dr. Krishna Kumari Challa on July 12, 2024 at 10:58am

Muscle fibers are composed of many components, such as various proteins, cell nuclei, organelles such as mitochondria, and molecular motors such as myosin that convert chemical fuel into motion and drive muscle contraction.
All of these components form a porous network that is bathed in water. So an appropriate, coarse-grained description for muscle is that of an active sponge, say the researchers.
But the squeezing process takes time to move water around, so the researchers suspected that this movement of water through the muscle fiber set an upper limit on how rapidly a muscle fiber can twitch.

To test their theory, they modeled muscle movements in multiple organisms across mammals, insects, birds, fish and reptiles, focusing on animals that use muscles for very fast motions. They found that muscles that produce sound, such as the rattle in a rattlesnake's tail, that can contract ten to hundreds of times per second typically don't rely on fluid flows. Instead, these contractions are controlled by the nervous system and are more strongly dictated by molecular properties, or the time it takes for molecular motors within cells to bind and generate forces.
But in smaller organisms, such as flying insects who are beating their wings a few hundred to a thousand times per second, these contractions are too fast for neurons to directly control. Here fluid flows are more important.
In these cases, the researchers found that fluid flows within the muscle fiber are important and their mechanism of active hydraulics is likely to limit the fastest rates of contraction.
The researchers also found that when muscle fibers act as an active sponge, the process also causes the muscles to act as an active elastic engine. When something is elastic, such as a rubber band, it stores energy as it tries to resist deformation. Imagine holding a rubber band between two fingers and pulling it back.

When you release the rubber band, the band also releases the energy stored when it was being stretched. In this case, energy is conserved—a basic law of physics that dictates that the amount of energy within a closed system should remain the same over time.
But when muscle converts chemical fuel into mechanical work, it can produce energy like an engine, violating the law of the conservation of energy. In this case, muscle shows a new property called "odd elasticity," where its response when squashed in one direction versus another is not mutual.

Unlike the rubber band, when muscle contracts and relaxes along its length, it also bulges out perpendicularly, and its energy does not stay the same. This allows muscle fibers to generate power from repetitive deformations, behaving as a soft engine.

These results are in contrast to prevailing thought, which focuses on molecular details and neglects the fact that muscles are long and filamentous, are hydrated, and have processes on multiple scales.
All together, our results suggest a revised view of how muscle functions is essential to understand its physiology. This is also crucial to understanding the origins, extent and limits that underlie the diverse forms of animal movement.

Suraj Shankar et al, Active hydraulics and odd elasticity of muscle fibres, Nature Physics (2024). DOI: 10.1038/s41567-024-02540-x

Part 2

Comment by Dr. Krishna Kumari Challa on July 12, 2024 at 10:53am

How water controls the speed of muscle contraction

The flow of water within a muscle fiber may dictate how quickly muscle can contract, according to a new study.

Nearly all animals use muscle to move, and it's been known for a long time that muscle, like all other cells, is composed of about 70% water. But researchers don't know what sets the range and upper limits of muscle performance. Previous research into how muscle works focused only on how it worked on a molecular level rather than how muscle fibers are shaped, that they are three-dimensional and are full of fluid.

Researchers now created a theoretical model of water's role in muscle contraction and found that how fluid moves through a muscle fiber determines how quickly a muscle fiber can contract.

They also found that muscle exhibits a new kind of elasticity called odd elasticity that allows muscle to generate power using three dimensional deformations, shown in a common observation that when a muscle fiber contracts lengthwise, it also bulges perpendicularly. Their results are published in the journal Nature Physics.

These results suggest that even such basic questions as how quickly muscle can contract or how many ways muscle can generate power have new and unexpected answers when one takes a more integrated and holistic view of muscle as a complex and hierarchically organized material rather than just a bag of molecules.

Part 1

Comment by Dr. Krishna Kumari Challa on July 12, 2024 at 9:29am

What made this bacterial glass different to other glasslike substances was the spontaneous formation of "microdomains" and the collective motion of the bacteria within these areas. These occurred where groups of the rod-shaped E. coli became aligned the same way.

The researchers were also surprised that the way the bacteria vitrify (turn into a glasslike state) apparently violates a physical law of typical thermal systems. What we characteristically know as glass, including colloidal glass, is classed as thermal glass. However, recently researchers have started to explore glassy states, like the one reported in this paper, which aren't considered thermal glass but share many of the same properties.

"Collections of 'self-propelled particles' like we see here have recently been regarded as a new kind of material called active matter, which is currently a hot topic and shows great potential.

Hisay Lama et al, Emergence of bacterial glass, PNAS Nexus (2024). DOI: 10.1093/pnasnexus/pgae238

Part 2

Comment by Dr. Krishna Kumari Challa on July 12, 2024 at 9:28am

Densely packed E. coli form an immobile material similar to colloidal glass, research shows

Dense E. coli bacteria have several similar qualities to colloidal glass, according to new research at the University of Tokyo. Colloids are substances made up of small particles suspended within a fluid, like ink for example. When these particles become higher in density and more packed together, they form a "glassy state."

When researchers multiplied E. coli bacteria within a confined area, they found that they exhibited similar characteristics. More surprisingly, they also showed some other unique properties not typically found in glass-state materials.

This study, which is published in PNAS Nexus, contributes to the understanding of glassy "active matter," a relatively new field of materials research which crosses physics and life science.

In the long term, the researchers hope that these results will contribute to developing materials with new functional capabilities, as well as aiding our understanding of biofilms (where microorganisms stick together to form layers on surfaces) and natural bacterial colonies.

Researchers have now found that the bacteria E. coli can behave in a similar way.

Since bacteria are very different from what we know of as glass, it was surprising that many of the statistical properties of glassy materials were the same for bacteria.

In this experiment, As the number of E. coli increased, they became caged in by their neighbors, restricting their ability to swim freely. Over time, they transitioned to a glassy state. This transition is similar to glass formation, as the researchers noted a rapid slowdown of movement, the caged-in effect and dynamic heterogeneity (whereby molecules travel longer distances in some areas but hardly move in others).

Part 1

Comment by Dr. Krishna Kumari Challa on July 12, 2024 at 9:21am

The researchers prepared human nasal tissue in the lab, growing it to resemble the surfaces of the human respiratory tract, then monitored gene expression changes over a 14-day 'infection.'
They found very limited production of inflammation molecules over time, which normally would be produced within hours of bacteria infecting human cells.

Researchers then applied both live and dead Haemophilus influenzae, showing the dead bacteria caused a fast production of the inflammation makers, while live bacteria prevented this.
This proved that the bacteria can actively reduce the human immune response.
If local immunity drops, for example during a viral infection, the bacteria may be able to 'take over' and cause a more severe infection.

 PLOS Pathogens (2024). journals.plos.org/plospathogen … journal.ppat.1012282

Part 2

Comment by Dr. Krishna Kumari Challa on July 12, 2024 at 9:19am

Respiratory bacteria 'turn off' immune system to survive, study finds

Researchers have identified how a common bacterium is able to manipulate the human immune system during respiratory infections and cause persistent illness. The research was published in PLOS Pathogens.

This study found the virulence mechanisms of Haemophilus influenzae, a bacterium that plays a significant role in worsening respiratory tract infections.

These bacteria are especially damaging to vulnerable groups, such as those with cystic fibrosis, asthma, the elderly, and Indigenous communities.

In some conditions, such as asthma and chronic obstructive pulmonary disease,

they can drastically worsen symptoms.

This research shows the bacterium persists by essentially turning off the body's immune responses, inducing a state of tolerance in human respiratory tissues.

Part 1

Comment by Dr. Krishna Kumari Challa on July 11, 2024 at 10:24am

Some environmental toxicants linked to depressive symptoms

Certain categories of environmental toxicants are associated with depressive symptoms, according to a study published online July 3 in JAMA Network Open.

Researchers  screened and assessed the associations between potential environmental toxicants and depressive symptoms among 3,427 participants from the 2013 to 2014 and 2015 to 2016 waves of the National Health and Nutrition Examination Survey. Exposures were assessed for 62 toxicants in 10 categories; the association with depression scores, measured by the 9-item Patient Health Questionnaire (PHQ-9), was examined.

The researchers identified associations between 27 chemical compounds or metals in six of 10 categories of environmental toxicants and the prevalence of depressive symptoms, including the volatile organic compound metabolites N-acetyl-S-(2 hydroxy-3-butenyl)-L-cysteine and total nicotine equivalent-2 (odds ratios, 1.74 and 1.42, respectively).

Compared with women and older individuals, men and younger individuals seemed more vulnerable to environmental toxicants. Overall, 5–19 percent of the associations were mediated by peripheral white blood cell count.

"This research highlights the significance of preventing and regulating important environmental toxicants to gain fresh insights into preventing and potentially treating depression," the authors write in their paper.

Jianhui Guo et al, Environmental Toxicant Exposure and Depressive Symptoms, JAMA Network Open (2024). DOI: 10.1001/jamanetworkopen.2024.20259

Comment by Dr. Krishna Kumari Challa on July 11, 2024 at 10:20am

Air pollution may affect lupus risk

New research published in Arthritis & Rheumatology indicates that chronic exposure to air pollutants may increase the risk of developing lupus, an autoimmune disease that affects multiple organs.

For the study, investigators analyzed data on 459,815 participants from the UK Biobank. A total of 399 lupus cases were identified during a median follow-up of 11.77 years. Air pollutant exposure was linked with a greater likelihood of developing lupus. Individuals with a high genetic risk and high air pollution exposure had the highest risk of developing lupus compared with those with low genetic risk and low air pollution exposure.

This study provides crucial insights into the air pollution contributing to autoimmune diseases. The findings can inform the development of stricter air quality regulations to mitigate exposure to harmful pollutants, thereby reducing the risk of lupus.

Air pollution, genetic susceptibility and risk of incident Systemic lupus erythematosus: A prospective cohort study, Arthritis & Rheumatology (2024). DOI: 10.1002/art.42929

**

Comment by Dr. Krishna Kumari Challa on July 11, 2024 at 10:01am

The geometry of life: Physicists determine what controls biofilm growth

This is physics helping biology.

From plaque sticking to teeth to scum on a pond, biofilms can be found nearly everywhere. These colonies of bacteria grow on implanted medical devices, our skin, contact lenses, and in our guts and lungs. They can be found in sewers and drainage systems, on the surface of plants, and even in the ocean.

Some research says that 80% of infections in human bodies can be attributed to the bacteria growing in biofilms.

The paper, "The biophysical basis of bacterial colony growth," was published in Nature Physics this week, and it shows that the fitness of a  biofilm- its ability to grow, expand, and absorb nutrients from the medium or the substrate—is largely impacted by the contact angle that the biofilm's edge makes with the substrate. The study also found that this geometry has a bigger influence on fitness than anything else, including the rate at which the cells can reproduce.

Understanding how biofilms grow—and what factors contribute to their growth rate—could lead to critical insights on controlling them, with applications for human health, like slowing the spread of infection or creating cleaner surfaces.

 Aawaz R. Pokhrel et al, The biophysical basis of bacterial colony growth, Nature Physics (2024). DOI: 10.1038/s41567-024-02572-3

Comment by Dr. Krishna Kumari Challa on July 11, 2024 at 9:54am

Subsurface of fingernails found to have precise tactile localization

Researchers found that humans have a surprisingly precise degree of tactile localization beneath their fingernails. In his study, published in the Proceedings of the Royal Society B, they tested how well volunteers could pinpoint the part of their fingernail being stimulated and outlines possible reasons.

Humans, like other primates, have nails on the ends of their fingers rather than claws—an evolutionary development that has not been explained. In this new effort, researchers investigated the sensitivity of the skin below the fingernails to learn more about how they were used by our ancestors.

The human fingernail does not have any nerves; thus, it cannot sense touch, pressure, heat, cold or other environmental characteristics. But there is skin beneath the fingernail that is capable of sensations, as evidenced by people who accidentally hit their thumb with a hammer or lose a nail.

To learn more about the sensitivity of the subsurface of the fingernail, the researchers recruited 38 adult volunteers. Each agreed to have their fingernails poked while they indicated on a photograph of a fingernail where they thought their fingernail was being touched. In the experiments, half of the volunteers had their nails touched by a stick, the other half by a filament. Only the thumb and middle finger were tested.

The study found that humans have highly precise localization in their nails—they can tell clearly which part of their nail is being touched. He suggests that this is due to mechanoreceptors called Pacinian corpuscles, buried in the skin beneath the nails. He notes that it is the same mechanism that allows blind people to localize touch using a cane. Pacinian corpuscles are able to detect small amounts of vibration, which happens when a slight impact occurs between a foreign object and a fingernail.

Why did humans develop fingernails instead of claws?  Why the skin beneath the nails is so sensitive? Researchers theorize that they likely served a sensorimotor function, giving humans more information about whatever their hands encounter.

Matthew R. Longo, Precise tactile localization on the human fingernail, Proceedings of the Royal Society B: Biological Sciences (2024). DOI: 10.1098/rspb.2024.1200

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