Integrin family of cell adhesion molecules in the injured brain: Regulation and cellular localization in the normal and regenerating mouse facial motor nucleus

Integrins are a large family of heterodimeric glycoproteins that play a cru cial role in cell adhesion during development, inflammation, and tissue rep air. In the current study, we investigated the localization of different in tegrin subunits in the mouse facial motor nucleus and their regulation afte r transection of the facial nerve. In the normal mouse brain, there was cle ar immunoreactivity for alpha 5-, alpha 6-, and beta 1-integrin subunits on blood vessel endothelia and for alpha M- and beta 2-subunits on resting pa renchymal microglia. Facial nerve transection led to an up-regulation of th e beta 1-subunit on the axotomized neurons and an increase in the alpha 4-, alpha 5-, alpha 6-, beta 1-, alpha M-, alpha X-, and beta 2-subunits on th e adjacent, activated microglia. Quantification of the microglial integrins revealed two different expression patterns. The subunits alpha 5 and alpha 6 showed a monophasic increase with a maximum at day 4, the alpha M-subuni t a biphasic regulation, with an early peak, at day 1 and an elevated plate au between day 14 and 42. At day 14, there was also an influx of lymphocyte s immunoreactive for the alpha 4 beta 1- and alpha L beta 2-integrins, whic h aggregated at sites of neural debris and phagocytotic microglia. This fin ding was accompanied by a significant increase of the alpha 5 beta 1-integr in on blood vessel endothelia. In summary, facial axotomy is followed by a strong and cell-type-specific expression of integrins on the affected neuro ns and on surrounding microglia, lymphocytes, and vascular endothelia. The presence of several, strikingly different temporal patterns suggests a sele ctive involvement of these molecules in the different adhesive events durin g regeneration in the central nervous system. (C) 1999 Wiley-Liss, Inc.