PPARγ signaling protects hair follicle stem cells from chemotherapy-induced apoptosis and epithelial-mesenchymal transition

BACKGROUND

Permanent chemotherapy-induced alopecia (pCIA), for which preventive interventions remain limited, can manifest with scarring. While the underlying pathomechanisms of pCIA are unclear, depletion of epithelial hair follicle (HF) stem cells (eHFSCs) is likely to play a role.

OBJECTIVES

To explore the hypothesis that eHFSCs undergo pathological epithelial-mesenchymal transition (EMT) besides apoptosis in pCIA, thus explaining the scarring phenotype. Furthermore, we tested whether a PPARγ modulator can prevent pCIA-associated pathomechanisms.

METHODS

Organ-cultured human scalp HFs were treated with the cyclophosphamide metabolite, 4-hydroperoxycyclophosphamide (4-HC). Additionally, HFs were pre-treated with the agnostic PPARγ modulator, N-Acetyl-GED-0507-34-Levo (NAGED), which we had previously shown to promote K15 expression and antagonize EMT in eHFSCs.

RESULTS

In accordance with anticipated hair bulb cytotoxicity, dystrophy and catagen induction, 4-HC promoted apoptosis along with increased p53 expression, DNA damage and pathological EMT in keratin 15+ (K15) bulge eHFSCs, as evidenced by decreased E-cadherin expression and the appearance of fibronectin- and vimentin-positive cells in the bulge. Pre-treatment with NAGED protected from 4-HC-induced hair bulb cytotoxicity/dystrophy, and halted apoptosis, p53 up-regulation, and EMT in the bulge, thereby significantly preventing the depletion of K15+ human eHFSCs ex vivo.

CONCLUSIONS

A cyclophosphamide metabolite alone suffices to damage and deplete human scalp eHFSCs by promoting apoptosis, DNA damage, and EMT ex vivo. Therefore, pCIA-therapeutic strategies need to target these pathological processes. Our data introduce the stimulation of PPARγ signaling as a novel intervention strategy for the prevention of pCIA, given the ability of NAGED to prevent chemotherapy-induced eHFSCs damage ex vivo.