Distinct roles for astrocyte alphavbeta5 and alphavbeta8 integrins in adhesion and migration

The alphav integrins are likely to be an important group of molecules for regulating astrocyte behaviour within the central nervous system. Together with their ligand vitronectin, they are expressed by astrocytes in vivo and are further upregulated during neurological disease. Here we have characterised the expression of alphav integrins on primary astrocytes from both rat and mouse, and shown that they express just two members, alphavbeta5 and alphavbeta8. By using RGD peptides and function-blocking antibodies against the beta1 integrins and alphavbeta5, we find that both alphavbeta5 and alphavbeta8 can act as functional receptors for vitronectin. However, while alphavbeta5 is largely responsible for astrocyte adhesion to vitronectin this integrin appears to play no role in migration on vitronectin, with alphavbeta8 playing the dominant role in promoting migration on this substrate. beta1 integrins are not involved in mediating interactions between astrocytes and vitronectin. These results were confirmed in experiments with astrocytes derived from mice in which the beta5 gene had been deleted by homologous recombination. beta5 null astrocytes attached to vitronectin at a reduced rate, but showed no defect in migration on vitronectin relative to wild-type astrocytes. These data provide the first evidence that alphavbeta8 regulates migration and show that astrocyte alphavbeta5 and alphavbeta8 integrins have distinct functions.