As the culmination of four years of work by the Slotkin laboratory’s graduate students, postdoctoral associates, and technicians, all of whom are represented as authors, their work has substantial implications for reducing the cost and effort that goes into producing transgenic crops. “Gene silencing is a key bottleneck that is inhibiting plant improvement… no matter what new trait a plant biologist works on, they are going to have to fight against the tidal wave of gene silencing,” said Slotkin. Normally, breeders need to start with thousands of plants to identify the few that express, instead of repress, the trait of interest. By discovering how and why DNA methylation occurs, this work enables crop breeders to avoid the silencing of the trait from the outset. “One day we could start with three plants instead of thousands. All of the time and money that is usually put into producing a crop is slimmed down,” said Slotkin.

Another major advancement of the work by Slotkin and his team was the establishment of a new model as to how gene silencing is initiated. One conventional theory in the field proposes that a critical protein called ‘RNA Polymerase V’ is present all across the genome and surveils different regions of genetic material to test for regions that need silencing. Once RNA Polymerase V identifies a gene region to silence, the DNA methylation process starts. However, in a breakthrough finding, the authors discovered that it is not the presence of RNA Polymerase V itself that triggers gene silencing, but rather the presence of small RNAs (which are critical for plant growth and development) that recruit RNA Polymerase V to the gene or transgene. “Our model is saying that small RNAs are driving RNA Polymerase V to the new location in the first place. If we get rid of the small RNA machinery, RNA Polymerase V doesn’t know where to go,” Slotkin described.

In addition, the methods used by the Slotkin team were just as valuable as their findings — the researchers overcame several significant technical hurdles in the process. As one example, gene silencing is typically studied as a cycle, rather than how it starts. Consequently, the researchers needed to do everything in the first generation of transgenic plants to watch the initiation of the process. “That’s a huge challenge,” Slotkin notes. “We plant thousands of seeds that may have integrated a transgene. Sometimes we only get five plants back because they did not transform well. This isn’t enough, as we want a lot of tissue off of them in order to measure DNA methylation… and these experiments require biological replicates, so more tissue is needed, and the experiment needs to be done again.” While it is a monumental amount of work to grow and regrow enough plants for such an experiment, “it is all worth it to be able to investigate the first generation of transgene silencing,” remarked Slotkin.

The first author of the paper is Meredith Sigman, a former graduate student at the Danforth Center, and the last author of the paper is Andrea McCue, a former postdoctoral associate in the Slotkin lab. The entire Slotkin research team continues to investigate the initiation of gene silencing. They explore fundamental questions regarding how DNA methylation is triggered and its potential contribution to overcoming obstacles in transgenic plant production. “We are at a crop research institute like the Danforth Center to make the plant improvement process easier for everyone,” concluded Slotkin.

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Materials provided by Donald Danforth Plant Science Center. Note: Content may be edited for style and length.

Neutrophils are a foundational part of the body’s immune system and the most abundant type of white blood cell, making up about 60 to 80 per cent of circulating immune cells in the blood. However, unlike other types of white blood cells, neutrophils are extremely short-lived and cannot be frozen and thawed like other immune cells, making them extremely difficult to examine, said study lead Shokrollah Elahi.

“Neutrophils live for hours to a day or two maximum,” Elahi said. “The body produces a lot of neutrophils, and they do their job and then they die and have to be regenerated in the bone marrow. But despite the fact that neutrophils are the most abundant white blood cells in the blood circulation, their role in the context of HIV has not been very well defined.”

In the study, published in the journal PLOS Biology, Elahi and his team examined the fresh blood of 116 people living with HIV and 60 individuals without the virus. They ran comprehensive sequencing on all the genes expressed in the neutrophils from both groups to determine any differences between them.

“We found that not all HIV-infected individuals have similar types of neutrophils,” said Elahi. “As the HIV disease progresses, neutrophils become more activated and more potent, and in turn activate the body’s T cells, which likely causes some of the problems associated with HIV infection such as inflammation and rapid aging.”

Elahi, a member of the Women and Children’s Health Research Institute, the Cancer Research Institute of Northern Alberta and the Li Ka Shing Institute of Virology, said neutrophils act like an early alarm system. When they detect a dangerous entity such as an invading microbe, they release proteins to signal other immune cells to the danger. This activation can be high or low, or more or less potent, depending on the severity of the danger and the reaction of other immune cells.

One of the proteins released by neutrophils is galectin-9, which Elahi previously linked to severe inflammation and cytokine storms in COVID-19 patients. Elahi’s team reported that when neutrophils sense a danger such as an infection, they become stressed and release the galectin-9. As the protein begins to saturate the blood, it can interact with different immune cells. For example, the team found that galectin-9 reacted strongly with T cells and made them more susceptible to HIV infection, causing a cascading effect that leads to a hyper-immune response and inflammation.

Elahi’s prior work showed that patients with HIV and some forms of cancer showed elevated levels of galectin-9 in their blood. However, in this latest study he was able to identify the major source of the protein.

“We found for the very first time that the neutrophil membrane, through a complex mechanism, is covered like a blanket with galectin-9,” he said. “When neutrophils become highly activated, the secretion of galectin-9 can activate T cells through interaction with another molecule called CD44, which then promotes chronic inflammation in HIV patients.”

Elahi’s study of neutrophils revealed that the “alarm” reaction of shedding proteins such as galectin-9 was associated with oxidative stress, a state in which the body is unable to naturally detoxify or remove certain oxygen-containing molecules that become harmful to cells. Oxidative stress is believed to play a role in the development of diseases including Parkinson’s, Alzheimer’s, cancer, heart failure and autism.

Based on his findings, Elahi said preventing galectin-9 shedding might be a powerful tool in reducing many of the negative effects of HIV infection. His team has already made some progress in reducing oxidative stress by using an organic antioxidant compound called phloretin and vitamin C.

“We have been looking at phloretin and vitamin C in the lab and our data are very promising,” Elahi said. “We know that both are good at reducing galectin-9 shedding, so we believe they can prevent the hyper-activation of neutrophils. We hope that our results will spark renewed investigation into the role of neutrophils in T cell activation in other acute and chronic conditions.”

Elahi noted the study reinforces that the most important thing for people who are living with HIV or are at risk of catching the virus is to get a screening test as soon as possible.

“If the virus is caught early and they can go on antiretroviral therapy, then it stops disease progression and reduces many of the complications associated with advanced HIV.”

“The body has a 24-hour internal clock, called circadian rhythm, that helps regulate physical and mental functioning,” said study author Dr. David Plans of the University of Exeter, UK. “While we cannot conclude causation from our study, the results suggest that early or late bedtimes may be more likely to disrupt the body clock, with adverse consequences for cardiovascular health.”

While numerous analyses have investigated the link between sleep duration and cardiovascular disease, the relationship between sleep timing and heart disease is underexplored. This study examined the association between objectively measured, rather than self-reported, sleep onset in a large sample of adults.

The study included 88,026 individuals in the UK Biobank recruited between 2006 and 2010. The average age was 61 years (range 43 to 79 years) and 58% were women. Data on sleep onset and waking up time were collected over seven days using a wrist-worn accelerometer. Participants completed demographic, lifestyle, health and physical assessments and questionnaires. They were then followed up for a new diagnosis of cardiovascular disease, which was defined as a heart attack, heart failure, chronic ischaemic heart disease, stroke, and transient ischaemic attack.

During an average follow-up of 5.7 years, 3,172 participants (3.6%) developed cardiovascular disease. Incidence was highest in those with sleep times at midnight or later and lowest in those with sleep onset from 10:00 to 10:59 pm.

The researchers analysed the association between sleep onset and cardiovascular events after adjusting for age, sex, sleep duration, sleep irregularity (defined as varied times of going to sleep and waking up), self-reported chronotype (early bird or night owl), smoking status, body mass index, diabetes, blood pressure, blood cholesterol and socioeconomic status.

Compared to sleep onset from 10:00 to 10:59 pm, there was a 25% higher risk of cardiovascular disease with a sleep onset at midnight or later, a 12% greater risk for 11:00 to 11:59 pm, and a 24% raised risk for falling asleep before 10:00 pm. In a further analysis by sex, the association with increased cardiovascular risk was stronger in women, with only sleep onset before 10:00 pm remaining significant for men.

Dr. Plans said: “Our study indicates that the optimum time to go to sleep is at a specific point in the body’s 24-hour cycle and deviations may be detrimental to health. The riskiest time was after midnight, potentially because it may reduce the likelihood of seeing morning light, which resets the body clock.”

Dr. Plans noted that the reasons for the observed stronger association between sleep onset and cardiovascular disease in women is unclear. He said: “It may be that there is a sex difference in how the endocrine system responds to a disruption in circadian rhythm. Alternatively, the older age of study participants could be a confounding factor since women’s cardiovascular risk increases post-menopause — meaning there may be no difference in the strength of the association between women and men.”

He concluded: “While the findings do not show causality, sleep timing has emerged as a potential cardiac risk factor — independent of other risk factors and sleep characteristics. If our findings are confirmed in other studies, sleep timing and basic sleep hygiene could be a low-cost public health target for lowering risk of heart disease.”

Now for the first time, a team at the University of South Florida Health (USF Health) Morsani College of Medicine, reports that before soluble fibrinogen is converted into insoluble fibrin molecules that can adversely accumulate, it can connect directly with neurons and cause a damaging inflammatory reaction. The researchers further discovered that fibrinogen specifically binds to two fibrinogen receptors on the surface of neurons: cellular prion protein (PrP^C) and intracellular adhesion molecule-1 (ICAM-1).

Their preclinical study was published Sept. 18 in a special issue entitled “Prions and Prion-Like Mechanisms in Disease and Biological Function” in MDPI–Biomolecules.

The findings have implications for identifying targeted therapies to help prevent or stop neurodegeneration in Alzheimer’s disease, traumatic brain injury, or other chronic neuroinflammatory diseases associated with abnormal vascular permeability (leakage) in the brain.

“Fibrinogen is one of the overlooked culprits involved in the processes of neurodegeneration and resulting memory loss,” said principal investigator David Lominadze, PhD, a USF Health professor of surgery, and molecular pharmacology and physiology. “Our study shows that fibrinogen is not only a marker (biological indicator) of inflammation but can be a cause of inflammation in the brain.”

Fibrinogen is a protein naturally produced in the liver and travels throughout the bloodstream to other organs and tissues. Outside of blood vessels, fibrinogen is converted by the enzyme thrombin into fibrin during blood clot formation, playing a key role in wound healing.

Dr. Lominadze’s laboratory focuses on understanding molecular changes affecting circulation of blood in the body’s smallest blood vessels — including how microvascular changes induced by inflammation may damage cognition, in particular short-term memory.

Dr. Lominadze and others have shown that inflammatory disease is associated with a higher concentration of fibrinogen in the blood, increased generation of potentially damaging free radicals, neuronal cell activation and microvascular permeability. In previous studies using their mouse model for mild-to-moderate traumatic brain injury, Dr. Lominadze’s group reported that fibrinogen after crossing the vascular wall accumulated in spaces between the microvessels and astrocytes (another brain cell type connecting vessels and neurons) and activated the astrocytes. This activation coincided with increased neurodegeneration and reduced short-term memory.

In this latest study the USF Health researchers tested whether fibrinogen, beside interacting with astrocytes, could connect directly with neurons — nerve cells critical for carrying information throughout the human body and coordinating all necessary functions of life.

They treated healthy mouse brain neurons grown in a petri dish with fibrinogen. Fibrinogen increased the death of these neurons, a process that was not influenced by the presence or absence of a thrombin inhibitor preventing the conversion of fibrinogen to fibrin. The finding suggests that soluble fibrinogen and, at later stages, fibrin can have similar toxic effects on neurons.

Furthermore, blocking the function of PrP^C and ICAM-1 fibrinogen receptors on the surface of neurons (essentially stopping fibrinogen from binding tightly to these receptors) reduced inflammatory reactions resulting in neurodegeneration.

“The study revealed that an interaction between fibrinogen and neurons induced an increase in the expression of proinflammatory cytokine interleukin-6 (IL-6), enhanced oxidative damage, and neuronal death, in part due to its direct association (contact) with neuronal PrP^C and ICAM-1,” the study authors wrote.

More research is needed. But altogether the USF Health study suggests that short-term memory problems stemming from neurodegenerative diseases with underlying inflammation may be alleviated by several interventions, Dr. Lominadze said. These include “dampening general inflammation, decreasing fibrinogen concentration in the blood by reducing the synthesis of fibrinogen, and blocking the binding of fibrinogen to its neuron receptors,” he said.

The USF Health research was supported by a grant from the National Heart, Lung and Blood Institute, part of the National Institutes of Health.

After looking at population size for the roughly 300 hunter-gatherer societies which existed until quite recently, the researchers found that many of these groups were much smaller than might have been expected from the local ecosystem productivity. In regions with short growing seasons, hunter-gatherer groups had smaller populations per square kilometre than groups who depended on abundant plant foods throughout the year.

Need for meat limited population size

“Basically, if people had to live through long dry or cold seasons when plant food was scarce, in order to survive they had to depend on hunting a very limited number of animals,” explains Galbraith, a professor in McGill’s Department of Earth and Planetary Sciences and at the ICTA-UAB (Institut de Ciència i Tecnologia Ambientals of the Autonomous University of Barcelona), and a senior author on the paper published recently in the journal Nature Ecology & Evolution.

“This led to a seasonal bottleneck in the amount of food available, which then set the overall limit on the population size, no matter how much food there was during the plentiful times.”

The team developed a mathematical model that simulates daily human foraging activities (gathering and hunting) and the resultant carbon (energy) flows between vegetation, animals, and hunter-gatherers in a realistic global environment.

“We were struck by the fact that — despite a long list of unknowns — a very strong result emerged from the model equations,” says Galbraith. “Wherever growing seasons were short, hunter gatherers required meat to make up a high percentage of their diets. And — just as in the modern world — it took much more land to produce the same amount of meat as plant-based food.”

The researchers then went back to look at the detailed ethnographic observations and found that, although its significance had not been noticed, this finding was well supported by records of hunter-gatherers including the Ache in the tropical forest, the Hiwi in the savannah, and the Bushmen groups in the Kalahari Desert. Due to similarities between the lifestyles of contemporary hunter gatherers and those of our foraging ancestors, it is likely that strong seasonality limited population sizes throughout our species’ past.

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Materials provided by McGill University. Note: Content may be edited for style and length.