The HF is one of the few organs that undergo cyclic involution and regeneration throughout life. Hair follicle structure, hair cycle and HFSC We also highlight the therapeutic implications of niche pathology with an aim to prevent hair loss and to promote hair growth.
In addition, we discuss how the influx or emergence of non-preexisting cells within the HFSC niche affects hair growth and depletes HFSCs. In diseased states, we discuss how the pathological changes of the niche lead to dysregulated hair growth. We review how HFSC activity is regulated by different signaling cells and how sensing and message-relaying cells help HFs to initiate a regenerative attempt in face of local injury and external environmental changes. We categorize the component cells of the HFSC niche into 3 groups according to their functions, including signaling, sensing and message-relaying. As the hair follicle (HF) is an integral part of skin, its growth and the activity of HFSCs are regulated by various nearby cells of the HFSC niche in the skin. Hair regeneration depends on the activation of hair follicle stem cells (HFSCs). Unwanted hair loss can pose psychosocial distress to affected individuals. Human hair, especially human scalp hair, also has important ornamental functions that are essential for social communication and senses of well-being.
REGION X HAIR SKIN
Hair forms a barrier to protect skin from external insults as well as to keep the body from temperature loss. Understanding the functions and pathological changes of the HFSC niche can provide new insight for the treatment of hair loss. dysfunction of dermal papilla cells in androgenetic alopecia and influx of auto-reacting T cells in alopecia areata and lichen planopilaris. Hair growth can be disrupted by niche pathology, e.g. Sympathetic nerves implement the message-relaying function by transmitting external light signals through an ipRGC-SCN-sympathetic circuit to facilitate hair regeneration. Macrophages capacitate the HFSC niche to sense tissue injury and mechanical cues and adipocytes seem to modulate HFSC activity in response to systemic nutritional states. Signaling modules, such as dermal papilla cells, immune cells and adipocytes, regulate HFSC activity through short-range cell-cell contact or paracrine effects. Using HFSCs as a model, we categorize niche cells into 3 functional modules, including signaling, sensing and message-relaying.
The cyclic growth of hair follicles is powered by hair follicle stem cells (HFSCs). In adaption to varying physiological conditions and the ever-changing external environment, the stem cell niche has evolved with multifunctionality that enables stem cells to detect these changes and to communicate with remote cells/tissues to tailor their activity for organismal needs. Stem cell activity is subject to non-cell-autonomous regulation from the local microenvironment, or niche.
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