The microanatomy of the distal arrector pili: possible role for alpha 1 beta 1 and alpha 5 beta 1 integrins in mediating cell-cell adhesion and anchorage to the extracellular matrix
Jk. Mendelson et al., The microanatomy of the distal arrector pili: possible role for alpha 1 beta 1 and alpha 5 beta 1 integrins in mediating cell-cell adhesion and anchorage to the extracellular matrix, J CUT PATH, 27(2), 2000, pp. 61-66
The arrector pili (AP) muscle is a small band of smooth muscle that attache
s proximally to the bulge area of the pilosebaceous apparatus in the reticu
lar dermis and extends up toward the epidermis. The distal anatomy of the A
P and the anchorage mechanism allowing hair erection have not been previous
ly described. Integrins are likely candidates mediating this attachment. Im
munohistochemical techniques were used to determine the distribution of the
following integrins: alpha 1, alpha 2, alpha 3, alpha 4, alpha 5, alpha 6
and beta 1 as well as fibronectin. Frozen human scalp tissue was sectioned
in traditional planes, obliquely and horizontally to visualize microanatomy
in three dimensions. Histological examination revealed that the distal por
tions of smooth muscle fibers splay extensively between collagen bundles of
the upper dermis. Integrin subunits alpha 1, alpha 5 and beta 1 were expre
ssed by the AP muscle. Analysis of the relative density of immunoreactivity
in digitized sections revealed increased alpha 5 subunit expression at the
extracellular matrix (ECM)-muscle interface. These data suggest that ancho
rage of the AP muscle to the ECM is via alpha 5 beta 1 integrin and alpha 1
beta 1 integrin functions in muscle cell-cell adhesion. Extensive splaying
of smooth muscle fibers may allow increased surface area contact between t
he ECM and smooth muscle cells expressing peripherally situated alpha 5 int
egrin.