Cyclic ADP-Ribose Modulates Intracellular Calcium Homeostasis and Anagen-Associated Signaling Pathways in Human Hair Follicle Dermal Papilla Cells

Background: Hair loss (alopecia) is primarily driven by the premature transition of hair follicles from the anagen (growth) to the catagen (regression) phase. Intracellular calcium signaling is implicated in hair follicle biology, including the regulation of Wnt/β-catenin activity and the modulation of catagen-associated factors such as TGF-β2. Cyclic ADP-ribose (cADPR), a calcium-mobilizing second messenger synthesized by CD38, has recently emerged as a potential modulator of intracellular calcium dynamics. This study investigated whether cADPR is associated with changes in intracellular calcium retention and anagen-associated signaling pathways in human hair follicle dermal papilla cells (HHDPCs). Methods: HHDPCs were treated with cADPR (0.001–0.5 ppm) and analyzed for cell viability, intracellular calcium retention, β-catenin-dependent transcription, and the gene expression of LEF-1 and TGF-β2. Cell viability was evaluated using the MTT assay, intracellular calcium content was quantified by ICP–OES, β-catenin activation was assessed using a TOPFlash luciferase assay, and gene expression was measured by qRT-PCR. Results: cADPR did not induce marked cytotoxicity, maintaining more than 98% cell viability across all concentrations. The highest response was observed at 0.05 ppm, at which intracellular calcium content remained elevated for up to six hours as assessed by ICP–OES. At this concentration, β-catenin-dependent transcription increased by approximately 2.3-fold relative to control, LEF-1 expression was significantly upregulated (~2.5-fold), and TGF-β2 expression was significantly downregulated (~0.3-fold). These responses showed an overall concentration-dependent trend across assays. Conclusions: These findings indicate an association between cADPR treatment and modulation of intracellular calcium retention and anagen-related signaling readouts in HHDPCs, supporting the need for further studies to establish mechanistic causality and physiological relevance.