A new study has unveiled a detailed molecular mechanism showing that cholesterol is a powerful promoter of hair regeneration.Published in Molecular Medicine, the research reveals that cholesterol stimulates hair growth by hijacking the body’s sympathetic nervous system (SNS), the network responsible for the “fight or flight” response, which in turn wakes up dormant hair follicle stem cells (HFSCs)
The findings offer new hope for developing therapies for hair loss by providing key insights into the biological pathways that regulate the hair growth cycle[
The PKA-TH-SNS Pathway: A Novel Regulator of Hair Growth
The research team, led by Xin Huang, focused on identifying the specific molecular steps that link cholesterol to hair regeneration.The core mechanism uncovered is a three-step signaling cascade
- Cholesterol Activates PKA: Subcutaneous injections of cholesterol in C57BL/6 mice were found to activate the Protein Kinase A (PKA) signaling pathway.
- PKA Phosphorylates Tyrosine Hydroxylase (TH): This PKA activation leads to the phosphorylation of tyrosine hydroxylase (TH) at the serine 40 residue (pTH Ser40). is the key, rate-limiting enzyme in the synthesis of catecholamines (like norepinephrine) that transmit signals in the sympathetic nervous system. Phosphorylation at the Ser40 site is particularly critical as it directly alters catecholamine synthesis and has the strongest impact on TH activity.
- SNS Activation Stimulates HFSCs: The enhanced TH phosphorylation then directly stimulates the sympathetic nervous system (SNS). This SNS activation, in turn, is what enhances the proliferation of hair follicle stem cells (HFSCs) and increases the proportion of hair follicles in the active anagen (growth) phase
In one experiment using PC12 cells, a cell line frequently used to study the sympathetic nervous system, cholesterol stimulation resulted in a gradual, time-dependent increase in the phosphorylation of TH at Ser40, directly demonstrating cholesterol’s ability to activate the sympathetic nervous system
Experimental Validation Confirms Mechanism
The researchers conducted multiple experiments to rigorously validate the critical steps in this newly identified pathway:
- Promoting Anagen Phase: Mice treated with cholesterol showed an earlier entry into the anagen phase and a significantly higher proportion of hair follicles in anagen compared to control mice, which remained mostly in the resting (telogen) or regressive (catagen) phases[. Subcutaneous cholesterol injections in C57BL/6 mice significantly enhanced hair regeneration by promoting HFSCs proliferation].
- HFSC Proliferation: Cholesterol treatment resulted in a significant increase in BrdU-positive cells, indicating a marked enhancement of HFSC proliferation compared to the control group. Cholesterol was also found to promote the proliferation of HFSCs by analyzing the proliferation marker Ki67 in the dorsal skin tissues.
- Ablating the Sympathetic Nerves: When the sympathetic nerves in the mice’s dorsal skin were chemically removed using the neurotoxin 6-hydroxydopamine (6-OHDA), the hair growth-promoting effects of cholesterol were significantly attenuated. This highlighted the critical regulatory role of the SNS in the process.
- Inhibiting PKA: Inhibiting the PKA pathway using HA-1004 prevented cholesterol from enhancing both TH phosphorylation and subsequent HFSC proliferation and hair growth. This action resulted in a significant slowdown of hair growth, with no significant difference between the cholesterol and control groups observed 28 days post-injection.
The study found that cholesterol exerted no significant effect on blood vessels or inflammatory immune cells in the hair follicle microenvironment. It also found that cholesterol did not directly stimulate HFSC proliferation in vitro (in a dish) , supporting the conclusion that its pro-growth effect is indirect, requiring the activation of the sympathetic nerves in the tissue.
New Hope for Hair Loss Treatments
Hair loss is a widespread concern, affecting an estimated 60-70% of the adult population globally. The current therapeutic options, such as minoxidil and finasteride, often have limited efficacy or side effects
The new findings suggest that targeting cholesterol-mediated signalling pathways could be a promising therapeutic approach for treating hair loss. Specifically, the identification of the PKA-tyrosine hydroxylase-SNS pathway as the regulatory route for hair regeneration offers a novel, efficient new strategy for treating alopecia. Further research is necessary to fully understand the long-term effects and the precise mechanism by which cholesterol activates the PKA pathway.
References
Guo, M., Jiang, J., Zhang, A., Yu, W. and Huang, X. (2025) ‘Cholesterol promotes hair growth through activating sympathetic nerves and enhancing the proliferation of hair follicle stem cells’. Molecular Medicine, 31(86). Available at: https://doi.org/10.1186/s10020-025-01139-z
