Researchers have discovered how stem cell-centric converging mechanisms caused by obesity can accelerate hair thinning, bringing new insights to tackle obesity complications and prevent hair loss.
According to the American Academy of Dermatologists, it is considered normal to shed anywhere between 50 to 100 hairs per day, and even more for people with longer hair. However, if you are noticing thinner hair on your scalp or bald patches on your head, it may be more than a simple case of temporary excessive hair fall – it may be a sign of hair loss. How, then, can we stop our hair from falling and our hairlines from receding? According to a group of researchers from Tokyo Medical and Dental University, eating less fat may be one way to save our hair.
Under normal circumstances, hair follicle stem cells renew themselves in every hair follicle cycle as part of the process that allows our hair to continuously grow back. However, as we age, hair follicle stem cells fail to replenish themselves, thereby causing hair thinning. Besides ageing, we know today that hair loss can be caused by a variety of reasons, including genetics, diet, and other medical conditions. For instance, androgenic alopecia – a common form of hair loss that usually begins above the temples – is often associated with obesity as it is often seen in overweight individuals. However, scientists have yet to confirm whether obesity truly accelerates hair thinning, and if so, how.
To find this missing link, Hironobu Morinaga and colleagues used mouse models to examine how obesity-induced stressors, such as those induced by a high-fat diet, or genetically induced obesity can affect hair follicle stem cells. They subjected two groups of adult mice to high-fat and standard diets and hypothesised that mice fed with high-fat diets would experience greater hair thinning and loss.
Their findings revealed that after merely four days of receiving high-fat diets, the mice developed bald patches. The lead author of the study, Morinaga, explained, “High-fat diet feeding accelerates hair thinning by depleting [hair follicle stem cells] that replenish mature cells that grow hair, especially in old mice.” But to precisely understand the reason behind this development, the researchers further “compared the gene expression in [hair follicle stem cells] between high-fat diet-fed mice and standard diet-fed mice and traced the fate of those [hair follicle stem cells] after their activation.”
Through chronological gene expression analysis, they found that feeding the mice with high-fat diet for four consecutive days directed the activated hair follicle stem cells towards epidermal keratinisation by generating excess reactive oxygen species. Integrated analysis using stem cell fate tracing, epigenetics, and reverse genetics also showed that feeding the mice with a high-fat diet can lead to the depletion of hair follicle stem cells by activating inflammatory signals and blocking hair follicle regeneration. In particular, Morinaga reported that “those [hair follicle stem cells] in high-fat diet-fed obese mice change[d] their fate into the skin surface corneocytes or sebocytes that secrete sebum upon their activation. Those mice show[ed] faster hair loss and smaller hair follicles along with depletion of [hair follicle stem cells]”.
“The gene expression in [hair follicle stem cells] from the high-fat-fed mice indicated the activation of inflammatory cytokine signalling within [hair follicle stem cells],” described Emi K. Nishimura, senior author. “The inflammatory signals in [hair follicle stem cells] strikingly repress Sonic hedgehog signalling that plays [a] crucial role in hair follicle regeneration in [hair follicle stem cells].”
The inhibition of Sonic hedgehog signal transduction in hair follicle stem cells can result in the further depletion of lipid-laden hair follicle stem cells through aberrant differentiation and inducing hair follicle miniaturisation and eventual hair loss. Conversely, when the scientists activated Sonic hedgehog signalling through transgenic and pharmacological means, they were able to rescue the depletion of hair follicle stem cells and reverse the effects of high-fat diet-induced hair loss. With these results, Nishimura firmly believes that “this could prevent hair loss brought on by the high-fat diet,” opening the door for future prevention and treatment strategies for hair thinning as well as to better understand obesity-related diseases.
Source: Morinaga et al. (2021). Obesity accelerates hair thinning by stem cell-centric converging mechanisms. Nature, 595, 266-271.