Hypoxia and reoxygenation of brain microvascular smooth muscle cells in vitro: cellular responses and expression of cerebral amyloid angiopathy-associated proteins

Hypoxia is known to cause complex cascades of physiological, biochemical, and morphological changes in the brain. Cerebral microvascular smooth muscle cell (MV-SMC) damage may occur following hypoxic conditions and lead to SMC dysfunction. However, little is known about the exact cellular and molecular responses of these cells to hypoxia. To partly address these questions, MV-SMC were isolated from human brain, cultured and placed in conditions of ambient hypoxia (H) and hypoxia followed by reoxygenation (H/R). Cell morphology, proliferation, and the expression of amyloid precursor protein (APP) and cystatin C peptide were investigated and compared (after induction of hypoxia) between cerebral MV- and human aortic SMC. Our results show that MV-SMC proliferation was inhibited after 48 h of hypoxia and H/R, whereas aortic SMC proliferation was stimulated after 48 h of hypoxia and H/R. Hypoxia and H/R induced an increase of intracellular APP and cystatin C expression in both types of SMC, though the effect of H and H/R on APP upregulation was quantitatively more robust in MV-SMC than aortic SMC. Patterns of hypoxia-induced APP upregulation in SMC differed significantly from those found in cultured neuronal cells (PC12, NT2). These results suggest that hypoxia and H/R-induced APP and cystatin C upregulation appear to occur independently of the inhibition of cerebral MV-SMC proliferation. Overexpression of APP and cystatin C in response to hypoxia may thus represent an initiating event in the pathogenesis of amyloid angiopathy, or mediate progression of this microvascular lesion.