They found that stem cells within hair follicles in mice given a high-fat diet behaved differently from those in mice with a standard diet. Inflammatory signals in the stem cells led to these differences, ultimately resulting in hair thinning and loss. These fascinating data shed light on the complicated link between obesity and organ dysfunction. It's well known that obesity is linked to the development of numerous diseases in humans. Heart disease, diabetes, and other ailments are extremely common in obese individuals. However, it's not fully clear how body organs specifically deteriorate and lose functionality from chronic obesity.
In a recent study, a group of researchers from Tokyo Medical and Dental University (TMDU) used mouse model experiments to examine how a high-fat diet or genetically induced obesity can affect hair thinning and loss. The authors found that obesity can lead to depletion of hair follicle stem cells (HFSCs) through the induction of certain inflammatory signals, blocking hair follicle regeneration and ultimately resulting in loss of hair follicles.
Normally, HFSCs self-renew every hair follicle cycle. This is part of the process that allows our hair to continuously grow back. As humans age, HFSCs fail to replenish themselves leading to fewer HFSCs and therefore hair thinning. Although overweight people have a higher risk of androgenic alopecia, whether obesity accelerates hair thinning, how and the molecular mechanisms have been largely unknown. The TMDU group aimed to address those questions and identified some of the mechanisms.
"High-fat diet feeding accelerates hair thinning by depleting HFSCs that replenish mature cells that grow hair, especially in old mice. We compared the gene expression in HFSCs between HFD-fed mice and standard diet-fed mice and traced the fate of those HFSCs after their activation," said the lead author of the study Hironobu Morinaga. "We found that those HFSCs in HFD-fed obese mice change their fate into the skin surface corneocytes or sebocytes that secrete sebum upon their activation. Those mice show the faster hair loss and smaller hair follicles along with depletion of HFSCs. Even with HFD feeding in four consecutive days, HFSCs shows increased oxidative stress and the signs of epidermal differentiation," Morinaga added.
"The gene expression in HFSCs from the high-fat-fed mice indicated the activation of inflammatory cytokine signalling within HFSCs. The inflammatory signals in HFSCs strikingly repress Sonic hedgehog signalling that plays a crucial role in hair follicle regeneration in HFSCs," described Emi K. Nishimura, a senior author. The researchers confirmed the activation of the Sonic hedgehog signalling pathway in this process can rescue the depletion of HFSCs.
"This could prevent the hair loss brought on by the high-fat diet," said Nishimura. This study has provided interesting new insights into the specific cellular fate changes and tissue dysfunction that can occur following a high-fat diet or genetically induced obesity and may open the door for future prevention and treatment of hair thinning as well as for the understanding of obesity-related diseases.