A New Mechanism to Explain Obesity-Induced Hair Loss.

Obesity in Mice Triggers Hair loss Through Stem Cell Depletion

There is a well known relationship between obesity and hair loss. A prior Taiwanese study, for example, showed that overweight and obese males had about a five times increased risk for severe forms of male balding compared to males who were not overweight. Obesity also impacts other hair loss conditions such as alopecia areata, acne keloidalis, dissecting cellulitis and psoriasis. We reviewed the relationship between obesity and hair loss last March on World Obesity Day.

In a new study published in Nature, a group of researchers from Tokyo Medical and Dental University (TMDU) showed that mice fed a high fat diet developed hair thinning and hair loss.

The key to the study was how this came about. Obese mice lost hair follicle stem cells through a mechanism that involved reactive oxygen species and generation of inflammatory signalling within hair follicle stem cells. This type of inflammatory signalling inhibited the normal regenerative signalling that occurs through a pathway known as the sonic hedgehog (SHH) pathway. The SHH pathway, for those who are unaware, is currently viewed as a key pathway in hair follicle regeneration. High fat diets blocked this pathway.

A high fat diet caused stem cells to undergo abnormal differentiation. In other words, stem cells were forced to change their job title from potent stem cells to skin surface corneocytes or sebum secreting sebocytes. This change was permanent since these new cell types are not able to produce new hairs. Therefore, the abnormal differentiation of stem cells caused a permanent loss of a hair producing stem cell from the finite pool of stem cells.

Mice fed a high fat diet showed progressive hair follicle miniaturization and hair loss. The change was shown to occur relatively quickly and even four days of eating a high fat diet triggered hair follicle stem cells to initiate the process of changing into other cell types.

This study provides new mechanistic insights into a well accepted notion that obesity affects the hair.

Reference

Morinaga, H., Mohri, Y., Grachtchouk, M. et al. Obesity accelerates hair thinning by stem cell-centric converging mechanisms. Nature 595, 266–271 (2021).