Sheep Cell Study Reveals How Dihydrotestosterone Boosts Hair Follicle Cell Growth by Silencing TGF-β Signalling

In a finding that could reshape how scientists think about the hormones behind hair growth, researchers in China have shown that dihydrotestosterone (DHT), the androgen notorious for driving male pattern baldness, can actually stimulate the proliferation of dermal papilla cells isolated from Hetian sheep by suppressing the TGF-β/Smad signalling pathway. The study, published in Veterinary Medicine and Science, offers the first established culture system for dermal papilla cells from this distinctive Xinjiang breed and provides a new experimental window into the molecular dialogue between androgens and the cells that orchestrate the hair follicle cycle. Because ovine skin closely resembles human skin in structure, thickness, follicular density and cyclic growth patterns, the work carries implications well beyond the wool industry, potentially informing research on androgenetic alopecia and other hair disorders in people.

Dermal papilla cells, or DPCs, sit at the base of the hair bulb and act as the command centre of the follicle. Richly supplied with blood vessels and nerves, they release a cocktail of paracrine signalling molecules, including vascular endothelial growth factor, fibroblast growth factors and Wnt ligands, that guide the proliferation and upward migration of surrounding follicular matrix cells. Those migrating cells then differentiate into the hair bulb and the inner and outer root sheaths, the protective sleeves that surround the growing hair shaft. DPCs effectively determine follicle size, the duration of the active growth phase known as anagen, and the overall rhythm of the hair cycle. When these cells malfunction, the consequences include follicle miniaturisation and atrophy, the hallmarks of conditions such as alopecia. Understanding what makes DPCs proliferate, and what holds them back, is therefore a central question in hair biology.

Androgens occupy a paradoxical position in this story. DHT, a potent metabolite of testosterone, promotes the growth of body hair in areas such as the beard and underarms, yet its excessive accumulation in genetically sensitive regions of the scalp drives androgenetic alopecia, the most common form of hair loss in humans. Previous studies have suggested that DHT may shift the balance between proliferation and apoptosis in DPCs by modulating pathways such as Wnt/β-catenin and TGF-β/Smad, but the precise mechanisms have remained elusive. The TGF-β superfamily comprises more than 30 ligands, including bone morphogenetic proteins, activins, inhibins and growth differentiation factors. In the canonical pathway, TGF-β ligands bind serine/threonine kinase receptors on the cell surface, triggering receptor-regulated Smads such as Smad2 and Smad3 to form complexes with the common mediator Smad4. These complexes enter the nucleus and regulate gene transcription, while inhibitory Smads such as Smad7 provide a built-in brake on the system.

The research team, working at Tarim University, chose their model with care. The Hetian sheep, an indigenous breed from the Hetian area of Xinjiang, is prized for high-quality wool and remarkable adaptation to extreme environments. Neonatal lambs, just three days old, were selected as donors because their dermal papilla cells show superior viability and proliferative potential, their low endogenous androgen levels minimise hormonal interference, and a uniform age group ensures biological consistency. Under institutional ethics approval, a small full-thickness skin sample was excised from the shaved dorsal skin of a healthy female lamb under local anaesthesia and strict aseptic conditions. The wound was treated with topical antibiotics and monitored daily until complete healing, reflecting the careful husbandry that underpins the entire cell culture enterprise.

Isolating the cells demanded considerable surgical precision at the microscopic scale. Skin specimens were minced into fragments and digested with collagenase type II at 37 degrees Celsius, after which intact hair follicles were separated by filtration and centrifugation. Using microdissection forceps and micro-spring scissors under a dissection microscope, researchers incised the narrowest region of the hair bulb, the dermal papilla neck, and gently detached the papilla with a glass capillary exploiting surface tension. Each isolated papilla was transferred to an individual well for primary culture. Within five days, polygonal cells migrated from the explants, forming growth halos that eventually covered half the well surface. By day twelve, the cultures had reached seventy to eighty percent confluency with a uniform, spindle-shaped morphology characteristic of healthy DPCs, and all nine replicate wells from the single donor were successfully established.

Identity verification was rigorous. Haematoxylin and eosin staining revealed cells with abundant nucleoli, while Giemsa staining highlighted the light-blue cytoplasm and central purplish-red nuclei. Chromosomal karyotype analysis confirmed 54 chromosomes per cell, comprising 26 pairs of autosomes and one pair of sex chromosomes, matching the standard sheep genome and proving the cells were genuinely of ovine origin. More decisively, double immunofluorescence staining demonstrated co-expression of CD133 and α-smooth muscle actin. CD133 is a surface marker highly expressed in human and murine DPCs but largely absent from other skin cell types, and recent hair follicle reconstitution assays have shown that CD133-high DPCs are the primary cellular drivers of new follicle formation. α-SMA, meanwhile, marks the contractile, myofibroblast-like properties that help DPCs maintain follicular structure. Together, these markers confirmed the cultures as authentic, hair-inductive dermal papilla cells.

With the model validated, the team turned to the central question: what does DHT do to these cells? Third-passage DPCs were treated with DHT concentrations spanning four orders of magnitude, from 1 to 1000 nanomolar, a range chosen to encompass physiologically relevant levels in androgen-responsive tissues and to extend into the supra-physiological realm to probe dose-dependent saturation. After 48 hours, the CCK-8 viability assay showed no significant differences across concentrations, but the more sensitive EdU assay, which directly measures DNA synthesis through flow cytometry, told a different story. Proliferation capacity rose steadily with increasing DHT concentration, peaking at 1000 nanomolar, where the difference from untreated controls reached statistical significance. The cells, in other words, were not merely surviving the hormone; they were dividing more vigorously in its presence.

The molecular explanation emerged from quantitative PCR analysis of eleven genes spanning the TGF-β ligand, receptor and Smad families. In cells treated with 1000 nanomolar DHT, expression of TGF-β1 and its receptor TGF-βRII was significantly downregulated, while TGF-β2 and TGF-β3 remained unchanged. Within the Smad family, DHT treatment reduced Smad2 and Smad6 expression, increased Smad5, and left Smad1, Smad3, Smad4 and Smad7 untouched. The pattern is mechanistically telling: Smad5 mediates BMP signalling, whereas Smad6 inhibits it, so the concurrent rise of Smad5 and fall of Smad6 suggests androgens may indirectly amplify BMP signalling, a pathway known to regulate follicle cycle timing, size and spacing. Meanwhile, the suppression of TGF-β1, a profibrotic cytokine that previous work has linked to reduced keratinocyte proliferation in co-culture, points to a release of the proliferative brake that TGF-β normally applies to the follicle microenvironment.

The authors are candid about the limits of the study. All experiments derived from a single biological donor, with replicates being technical rather than biological, and the pathway conclusions rest on gene expression data alone. Protein-level validation by Western blot, rescue experiments using exogenous TGF-β1 or pharmacological Smad inhibition, and in vivo or three-dimensional culture systems would all strengthen the causal chain between DHT, TGF-β/Smad suppression and DPC proliferation. The contrast with human scalp DPCs, where DHT has been reported to delay cell cycle progression without boosting proliferation, also underscores how tissue-specific and species-specific androgen responses can be; androgenetic alopecia is confined to genetically sensitive scalp regions and does not occur in normal skin. Even so, the establishment of the first Hetian sheep DPC culture is a genuine advance. It links androgen regulation to follicle development in a system directly relevant to wool fibre quality, potentially supporting higher wool yields and greater economic value for a distinctive livestock breed, while offering human hair researchers a comparative model whose skin biology mirrors our own more closely than rodents ever could. For a hormone best known for taking hair away, DHT has just revealed a surprising talent for building it, at least in sheep.

Subject of Research: Androgen regulation of dermal papilla cell proliferation via the TGF-β/Smad signalling pathway in Hetian sheep

Article Title: Dihydrotestosterone Promotes Hetian Sheep Dermal Papilla Cell Proliferation by Inhibiting the TGF‐β/Smad Signalling Pathway

Article References: Wang, Q., Liu, X., Feng, Z., Zhang, J., Li, C., Shi, R., & Li, S. (2026). Dihydrotestosterone Promotes Hetian Sheep Dermal Papilla Cell Proliferation by Inhibiting the TGF‐β/Smad Signalling Pathway. Veterinary Medicine and Science, 12(5), Article e71118. https://doi.org/10.1002/vms3.71118

Image Credits: AI Generated

DOI: 10.1002/vms3.71118

Keywords: dihydrotestosterone, dermal papilla cells, TGF-β/Smad pathway, Hetian sheep, hair follicle, androgenetic alopecia, wool quality, cell proliferation, Smad signalling, hair biology, Xinjiang livestock, primary cell culture