Self‐organizing hair peg‐like structures from dissociated skin progenitor cells: New insights for human hair follicle organoid engineering and Turing patterning in an asymmetric morphogenetic field

Abstract

Human skin progenitor cells will form new hair follicles, although at a low efficiency, when injected into nude mouse skin. To better study and improve upon this regenerative process, we developed an in vitro system to analyse the morphogenetic cell behaviour in detail and modulate physical‐chemical parameters to more effectively generate hair primordia. In this three‐dimensional culture, dissociated human neonatal foreskin keratinocytes self‐assembled into a planar epidermal layer while fetal scalp dermal cells coalesced into stripes, then large clusters, and finally small clusters resembling dermal condensations. At sites of dermal clustering, subjacent epidermal cells protruded to form hair peg‐like structures, molecularly resembling hair pegs within the sequence of follicular development. The hair peg‐like structures emerged in a coordinated, formative wave, moving from periphery to centre, suggesting that the droplet culture constitutes a microcosm with an asymmetric morphogenetic field. In vivo, hair follicle populations also form in a progressive wave, implying the summation of local periodic patterning events with an asymmetric global influence. To further understand this global patterning process, we developed a mathematical simulation using Turing activator‐inhibitor principles in an asymmetric morphogenetic field. Together, our culture system provides a suitable platform to (a) analyse the self‐assembly behaviour of hair progenitor cells into periodically arranged hair primordia and (b) identify parameters that impact the formation of hair primordia in an asymmetric morphogenetic field. This understanding will enhance our future ability to successfully engineer human hair follicle organoids.

More than just bricks and mortar: Fibroblasts and ECM in skin health and disease

“…33 41,42 the efficacy of this phenomenon drops as a factor of developmental age and remains low in a human system. 43…”

“…A better understanding of lineage potential by diverse skin fibroblasts is required to advance the efficiency of hair follicle reconstitution from dissociated skin cells. While hair follicles readily reconstitute from newborn mouse keratinocytes and fibroblasts, 41,42 the efficacy of this phenomenon drops as a factor of developmental age and remains low in a human system 43 …”

“Two-Cell Assemblage” Assay: A Simple in vitro Method for Screening Hair Growth-Promoting Compounds

“…We observed that the dissociated hORS cells encapsulated the hDP cell mass without any manipulation. Indeed, it has previously been found that dissociated skin cells have the potential to undergo a selforganization process (Lei et al, 2017a;Weber et al, 2019). The inner core-outer shell micro structures with unipolar orientation were not limited to our hORS and DP cell coculture model.…”

Pre-aggregation of scalp progenitor dermal and epidermal stem cells activates the WNT pathway and promotes hair follicle formation in in vitro and in vivo systems

“…Since the formation of type I aggregates reflects the regeneration potential of scalp dermal cells and the morphology or organization of epidermal and dermal cells of type I aggregates is reminiscent of the structure of early-stage hair follicles [13], we wondered if type I aggregates represent nascent hair follicles. Therefore, we characterized the structure of type I aggregates formed at 3 days by performing histological analysis and IF staining.…”

“…Hair follicles are dynamic structures that have a wide range of functions including sensory activity, skin moisture retention, thermoregulation, and esthetic appearance [12]. Recently, Weber et al successfully regenerated hair peg-like structures from fresh fetal scalp-derived dermal progenitor cells combined with cultured neonatal foreskins using a droplet method in vitro [13]. That was the first report of an in vitro generation of human hair follicle organoids; however, the dermal cells had not been expanded in culture and the droplet method is not practical to generate large-scale organoids for research and clinical applications such as screening assays.…”