Projecting villi in the small intestine vastly increase the surface area of the gut, increasing its ability to absorb nutrients. Some food particles are visible in one of the crevices between villi. Scanning electron micrograph courtesy of Alan Boyde, Wellcome Images.
Signaling intestinal distress
Researchers at the University of California, San Diego School of Medicine have identified the signaling pathway involved in viral infections that provokes the intestinal epithelial cell death seen in some of those infections and other intestinal disorders like celiac disease.
The results of the study led by Martin F. Kagnoff, MD, professor of medicine and pediatrics and director of the Laboratory of Mucosal Immunology at UC San Diego, and colleagues, shows that double-stranded RNA (dsRNA), which is characteristic of certain viral infections, activates a Toll-like receptor 3 (TLR3) signaling pathway in the intestinal epithelial cells that line the small intestine and results in the death of those cells. Their study has been published in the January 1 edition of The Journal of Immunology.
Disorders of the small intestine, including celiac disease and certain intestinal virus infections such as Rotavirus infection, are characterized by villus shortening in the small intestine and abnormalities in the absorption of nutrients. Intestinal epithelia cells (IECs) form the surface lining of small intestinal villi, which are finger-like projections that increase the surface area available for the absorption of nutrients from digested food.
It is those IECs that are the targets of the dsRNA-induced cell death – a result of apoptosis, or programmed cell death – resulting in shortening of the villi and diarrhea. Importantly, despite dramatic changes to the small intestine, the researchers found that such damage to the small intestinal structure was transient, since mice exposed to dsRNA survived and intestinal structure returned to normal within 48 hours.
Hair today and tomorrow
Though it’s sometimes too thin and sparse to be easily visible, hair covers the entire human body with a few obvious exceptions: our lips, palm of our hands and bottoms of our feet. Hair sprouts from skin organs called follicles, which contain a group of epithelial cells and melanocytes that rapidly divide to produce the hair fiber. The hair follicle is connected to the epidermis by a set of muscles called arrector pili, which push the hair up and create “goosebumps.” Near these muscles are groups of stem cells residing in a structure called “the bulge,” colored blue in this confocal microscopy image of mouse epidermis by Ian Smyth of Monash University in Australia. These stem cells continually supply the follicle with hair-producing cells.