Chronic overproduction of transforming growth factor-β1 by astrocytes promotes Alzheimer's disease-like microvascular degeneration in transgenic mice

Cerebrovascular amyloid deposition and microvascular degeneration are frequently associated with Alzheimer's disease (AD), but the etiology and pathogenetic role of these abnormalities are unknown, Recently, transforming growth factor-beta 1 (TGF-beta 1) was implicated in cerebrovascular amyloid formation in transgenic mice with astroglial overproduction of TGF-beta 1 and in AD. We tested whether TGF-beta 1 overproduction induces AD-like cerebrovascular degeneration and analyzed how cerebrovascular abnormalities develop over time in TGF-beta 1-transgenic mice. In cerebral microvessels from 3- to 4-month-old TGF-beta 1-transgenic mice, which display a prominent perivascular astrocytosis, levels of the basement membrane proteins perlecan and fibronectin were severalfold higher than in vessels from nontransgenic mice. Consistent with this increase, cortical capillary basement membranes of TGF-beta 1 mice were significantly thickened, These changes preceded amyloid deposition, which began at around 6 months of age. In 9- and 18-month-old TGF-beta 1 mice, various degenerative changes in microvascular cells of the brain were observed. Endothelial cells were thinner and displayed abnormal, microvilli-like protrusions as well as occasional condensation of chromatin, and pericytes occupied smaller areas in capillary profiles than in nontransgenic controls. Similar cerebrovascular abnormalities have been reported in AD. Wie conclude that chronic overproduction of TGF-beta 1 triggers an accumulation of basement mem brane proteins and results in AD-like cerebrovascular amyloidosis and microvascular degeneration. Closely related processes may induce cerebrovascular pathology in AD.