Cardiovascular Research Advance Access originally published online on May 9, 2008
Cardiovascular Research 2008 79(1):1-2; doi:10.1093/cvr/cvn117
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One more reason to save your hair
Department of Anatomy, University Clinic Essen, 55 Hufelanstrasse, D-45147 Essen, Germany
* Corresponding author. Tel: +1 353 716 6958. E-mail address: dimitri.scholz{at}ucd.ie
Hair follicles are self-renewing structures that cycle and reconstitute themselves throughout life because they contain keratinocyte stem cells.1 After new evidence has been presented about hair follicle cells differentiating into adipogenic, osteogenic, chondrogenic, myogenic, neuronal, and glial2–5 lineages, the question arises whether these cell possess other abilities and whether they are pluri- or even omnipotent. In this context, the work by Liu et al.6 in this issue of Cardiovascular Research inserts an important piece into the hair follicle puzzle. It presents clear evidence for the conversion of hair follicle stem cells into smooth muscle cells that have the ability to contract.
The construction of functional tissue-engineered blood vessels from progenitor cells is a declared goal for this group.6,7 Lack of availability of autologous vascular grafts and the pain and discomfort associated with the donor site necessitate the development of tissue-engineered blood vessels for tissue regeneration. One of the major challenges is to get an easily accessible, autologous source of progenitor cells. The hair follicle seems to be a lucky one. Since not only the hair follicle but also the hair bulge region have been shown to be a niche for stem cells, probably for multipotent stem cells with the capability to differentiate into different cutaneous lineages,8,9 hair can be considered to be important not only for social self-esteem and sexual communication but also for tissue repair and regeneration. One of the crucial prerequisites for functioning tissue engineering is the presence of an adequate vascular network primarily formed by endothelial and smooth muscle cells.
Previous work published by Amoh et al.10 demonstrated the generation of endothelial cells and subsequent forming of blood vessels from the hair follicle region. Now, the work of Liu et al.6 demonstrates the generation of contractile smooth muscle cells from the hair follicle region. Considering the potential presence of mesenchymal stem cells in the hair follicle bulge region which can serve for the generation of fibroblasts, among several other cell types, the question arises whether hair can be used for engineering of functioning blood vessels. Indeed, the presence of stem cells that differentiate into all cell types needed for vascular formation and stabilization in the same tissue region, including endothelial and smooth muscle cells and fibroblasts, would imply that these cells can be manipulated concertedly, enabling the formation of endothelial tubes covered by peri-endothelial cells such as pericytes or smooth muscle cells. The presence and regular assembly of both of these cell types in the wall of newly formed blood vessels is not only necessary for the survival of the vessels but also for the capacity of structural remodelling of blood vessels, which depends on tissue demand and vascular perfusion. Future work will show whether the generation of blood vessels from hair, say postnatal vasculogenesis from hair, remains merely a prediction or not. Regardless of the uncertainty, we would advise everybody to save their hair.
Generally speaking, stem cells attract high attention worldwide. Hairs with stem cells, particularly with those of potential pluripotency, have become more attractive than previously. Pluripotent stem cells have the capacity to give rise to cell types of all three germ layers.11 Principally, one would get all tissue and organ cell types needed for tissue regeneration or construction once the ‘cocktails’ needed for the specific differentiation of these cells are characterized and/or available. Based on such conceivability, the prediction would be that one day every disease can be treated and every tissue defect can be repaired using such stem cells. The hope is big, and so is the hype. Moreover, in comparison to apoptosis, angiogenesis, primary cilia, and other ‘trendy’ directions, stem cells are politically more active. US conservatives together with European ‘Greens’ try to prohibit some studies, and suddenly everybody has an opinion as with genetically modified tomatoes or euthanasia. Because of this high degree of public interest, we have to apply especially high standards to new studies from the milieu of stem-cell breeders. To prove the conversion of a stem cell into a differentiated cell, it is not enough to demonstrate the presence of some immunological markers. Anyone who has worked with cells in culture knows that those markers are not 100% trustworthy in vitro, especially in the ‘borderline’ situation when the cell is differentiating from a progenitor cell and can express a wild bunch of markers. Thus, several markers expressed in different types of unipotent progenitor or multipotent stem cells and the overlapping finding make a better characterization of these cells difficult. On the other hand, the additional functional analysis combined with the ultrastructural study presented by Liu et al.6 sets new standards for future stem-cell studies. Cells that look like smooth muscle cells under the light and electron microscope, express specific smooth muscle cell markers, and contract should be smooth muscle cells. For future studies, the most urgent question for cardiovascular biology could be whether the hair follicle stem cells could also differentiate into cardiomyocytes and fibroblasts to construct functioning new tissue or replace damaged tissue.
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The opinions expressed in this article are not necessarily those of the Editors of Cardiovascular Research or of the European Society of Cardiology.
Present address: Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Dublin 4, Ireland 
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