Authors and affiliations
Talveen Purba1, Iain Haslam1, Asim Shahmalak2, Ralf Paus1,3
The Dermatology Centre, Salford Royal NHS Foundation Trust and Institute of Inflammation and Repair, University of Manchester, Manchester, United Kingdom
Crown Clinic, Thorley House, Bailey Ln, Manchester
Department of Dermatology, University of Münster, Münster, Germany
The localisation of putative markers of epithelial hair follicle stem cell (eHFSC) sub-populations, delineated in the murine pelage follicle in recent years, remains poorly defined within the human hair follicle (HF). Using immunofluorescence, we have characterised eHFSC sub-populations that express the murine eHFSC markers, Sox9 and Lhx2, in isolated human occipital scalp HFs from patients undergoing HF transplantation surgery (n=>3) relative to each other and to the well-known human eHFSC markers, keratin 15 (K15) and keratin 19 (K19). In the murine HF, transcription factor Sox9 is thought to be involved in the regulation of outer root sheath (ORS) differentiation and maintenance of the eHFSC niche. Moreover Sox9+ murine eHFSCs are capable of contributing to all HF epithelial lineages. In the human HF, Sox9 immunoreactivity (IR) showed both basal and suprabasal localisation throughout the ORS. Double immunofluorescence showed that a subset of Sox9+ cells co-expressed K15+ and K19+ in the basal bulge and suprabulbar ORS. Sox9 expression patterns in the ORS were prominently cytoplasmic, but were on occasion observed to show nuclear compartmentalisation, possibly corresponding to cell quiescence and differentiation respectively. Antibody to transcription factor Lhx2, which is required in eHFSC niche organisation and quiescence in murine HFs, demonstrated prominent IR within a small number of cells in the ORS. The intermittent distribution of Lhx2 IR in the ORS was reminiscent of that of K19+ cells, which localise to the bulge, infra-bulge and suprabulbar ORS. Further investigation highlighted that Lhx2 demarcated cells that were both K19+ and K19-. Moreover, double immunofluorescence also highlighted both ORS cells that expressed either Lhx2 or Sox9 and cells that were Lhx2/Sox9 double-positive. The data presented here emphasises that the human ORS is enriched with a heterogeneous collective of epithelial stem/progenitor cells. We therefore seek to further explore and understand these different eHFSC sub-populations and demarcate their hierarchical organisation with respect to quiescence, cell cycle activation and differentiation in the healthy human HF by applying additional relevant in situ markers.
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