Hair follicle-associated-pluripotent (HAP) stem cells

Abstract

Various types of stem cells reside in the skin, including keratinocyte progenitor cells, melanocyte progenitor cells, skin-derived precursors (SKPs), and nestin-expressing hair follicle-associated-pluripotent (HAP) stem cells. HAP stem cells, located in the bulge area of the hair follicle, have been shown to differentiate to nerve cells, glial cells, keratinocytes, smooth muscle cells, cardiac muscle cells, and melanocytes. HAP stem cells are positive for the stem-cell marker CD34, as well as K15-negative, suggesting their relatively undifferentiated state. Therefore, HAP stem cells may be the most primitive stem cells in the skin. Moreover, HAP stem cells can regenerate the epidermis and at least parts of the hair follicle. These results suggest that HAP stem cells may be the origin of other stem cells in the skin. Transplanted HAP stem cells promote the recovery of peripheral-nerve and spinal-cord injuries and have the potential for heart regeneration as well. HAP stem cells are readily accessible from everyone, do not form tumors, and can be cryopreserved without loss of differentiation potential. These results suggest that HAP stem cells may have greater potential than iPS or ES cells for regenerative medicine.

Keywords: Hair follicle; bulge area; cardiac muscle cell; differentiation; nestin; neuron; stem cell.

Figure 1.

The location of various types of stem cells in the skin.

Figure 2.

Rejoining severed sciatic nerves with HAP stem cells. (a) Schematic of vibrissa follicle of GFP transgenic mice showing the position of GFP- and nestin-expressing vibrissa follicle HAP stem cells (red arrows) (a1). Colony formed from GFP-expressing HAP stem cells from the vibrissa after 2 months in culture (a2). GFP-expressing HAP stem cells within the colony were nestin-positive (a3). (b) GFP-expressing HAP stem cells grown for 2 months in DMEM-F12 containing B-27, 1% methylcellulose, and bFGF were transplanted between the severed sciatic nerve fragments in C57BL/6 immunocompetent mice (blue arrow). (c) Fluorescence images from a live mouse. Two months after transplantation between the severed sciatic nerve, the GFP-expressing HAP stem cells joined the severed sciatic nerve. (c2) Higher magnification of (c1). (d) Bright field (d1) and fluorescence (d2) images of an excised sciatic nerve.

Figure 3.

GFP-expressing vibrissa HAP stem cells were growing in the joined sciatic nerve. (a) Transverse section of joined nerve. In the marginal area of the joined nerve, GFP-expressing HAP stem cells formed many myelin sheaths (white arrows). (a2) Higher magnification of area of (a1) indicated by the white dashed box. (b) Most of the GFP-expressing vibrissa HAP stem cells differentiated to Schwann cells and formed myelin sheaths surrounding axons.

Figure 4.

Mouse HAP stem cells differentiated to beating cardiac muscle cells. (a) Schematic of separated vibrissa hair follicle. (b) The mouse vibrissa hair follicle was separated into 3 parts (upper, middle, and lower part), and suspended separately in DMEM containing 10% FBS. (c) Two weeks after culture, all 3 parts (upper, middle, and lower part) of the hair follicle, cultured in DMEM with FBS, differentiated to troponin- and desmin-positive cardiac muscle cells. The number of cardiac-muscle cells was significantly higher in the upper part compared with the middle and lower parts of the hair follicle. Bars = 100 µm.

Figure 5.

Nestin-expressing human HAP (hHAP) stem cell colonies differentiated to cardiac muscle and other types of cells. (a) hHAP stem cell colonies are SSEA1-negative, SSEA3-, SSEA4-, Nanog-, Oct3/4-, and nestin-positive. Scale bar = 100 µm. (b) Two weeks after transfer to DMEM containing 10% FBS, the nestin-expressing hHAP stem-cell colonies differentiated to nestin- and βIII-tubulin-positive neurons, GFAP-positive glial cells, K15-positive keratinocytes, smooth muscle actin-positive smooth muscle cells, and troponin (cTnT)-positive cardiac-muscle cells. Scale bar = 100 µm.