By Pat Bailey
The curtain cloaking how AIDS and HIV (human immunodeficiency virus) impact the human digestive and immune systems has been drawn back a bit further, thanks to a team of researchers from UC Davis’ departments of Food Science and Technology and Medical Microbiology and Immunology.
The small intestine is extremely difficult to study because of its location in the body but plays a critical role in human health. Its inner lining offers both a portal for absorbing nutrients and a barrier against toxins or invasive microbes.
Using rhesus macaque monkeys as a research model, the scientists examined gene expression of both naturally occurring gut bacteria and an introduced probiotic bacterium, Lactobacillus plantarum, in the small intestine.
Figures: Microbial gene expression lights up in green in the small intestine of SIV-infected monkeys without (left) and with (right) Lactobacillus. Images by Lauren Hirao and Irina Grishna.
They then compared the gene activity of those bacteria in healthy animals to that of the same bacteria during the first few days of infection with SIV (simian immunodeficiency virus), the monkey version of HIV.
Their findings are reported online in the open-access journal Nature Scientific Reports.
“This is a new approach to investigating how bacteria interact with the small intestine during times of health and disease,” said study co-author Maria Marco, a microbiologist in the Department of Food Science and Technology, who studies the effects of ‘beneficial’ bacteria.
By looking at their gene expression patterns, Marco and colleagues found that both the native and introduced bacteria appeared to be consuming sugars produced by the intestinal cells.
The researchers also showed that both L. plantarum and the native microbes responded the same way in the small intestine of healthy rhesus macaques as they did in the small intestine of macaques in the very early stage of SIV infection. This indicates that the transcriptomes—the entire collections of mRNA sequences in a cell—for these bacteria are not altered shortly after SIV infection.
“The effects of SIV infection were clearly very minor for both types of bacteria,” Marco said.
She noted, however, that in a study published last year, co-author Satya Dandekar, professor of medical microbiology and immunology and colleagues showed that L. plantarum was able to reverse some of the damage to the small intestine’s epithelium, or thin inner lining, which had been caused by SIV infection only a few days after exposure to the virus. That study also used rhesus macaques as an animal model.
“Such discoveries related to how bacteria adapt to the small intestine, help us to develop a clearer picture of how the lining of the small intestine is impacted during chronic HIV infection and, we hope, will lead to new strategies for manipulating native gut microbes to alleviate such intestinal damage,” she said.
Collaborating with Marco and Dandekar were co-authors Benjamin Golomb, formerly of the Department of Food Science and Technology, and Lauren A. Hirao Department of Medical Microbiology and Immunology.
The cross-campus collaborative effort was largely initiated by the UC Davis RISE (Research Investments in the Sciences and Engineering) grant program. Funding for the study was provided by the National Institutes of Health, the U.S. Department of Agriculture – National Institute of Food and Agriculture, and the California HIV/AIDS Research Program.
Pat Bailey writes about agricultural and veterinary sciences for UC Davis Strategic Communications. Follow her on Twitter @UCDavis_Bailey.