Pharmacological inhibition of carbonic anhydrases ameliorates cognitive dysfunction, rescuing Aβ‐induced neurovascular pathology in vivo

Abstract

Cerebrovascular dysfunction (CVD) is an early feature of Alzheimer's disease (AD), contributing to the pathology progression, and suggesting a strict association between CVD and neurodegeneration. The majority of AD cases present cerebral amyloid angiopathy (CAA), neuropathological feature characterized by abnormal vasculotropic deposition of amyloid beta, mainly Aβ40. Severe CAA is also induced by familial Aβ variants, such as the Dutch-Q22. Our previous in vitro studies demonstrated that brain vascular amyloidosis elicits mitochondrial dysregulation and caspase-mediated apoptosis, in cells composing the neurovascular unit, including neurons, endothelial, glial and smooth muscle cells. Additionally, we showed that acetazolamide (ATZ) and methazolamide (MTZ), FDA-approved carbonic anhydrase inhibitors (CAIs) which cross the blood-brain barrier (BBB), hamper these detrimental processes. Carbonic anhydrases (CAs) represent a family of metalloenzymes catalyzing the reversible hydration of carbon dioxide, and their inhibition improves cerebral blood flow, vasoreactivity and neuronal excitability, pointing to CAs as CVD targets in AD.We employed Tg-SwDI mice (expressing human amyloid precursor protein, APP, carrying the Swedish, Dutch and Iowa mutations), which develop fibrillar amyloid burden, primarily in the cerebral microvasculature, starting at 6 months. We fed the animals (from 8 to 16 months of age) a CAI-diet, following which we performed behavioral analysis, and harvested the brains for both biochemical and immunohistochemical examination.Compared to untreated Tg mice, ATZ- and MTZ-fed animals showed reduced cognitive impairment, along with decreased vascular Aβ overload and astrogliosis, main pathological hallmarks of the disease. Tg animals exhibited Aβ deposition in endothelial and glial cells, leading to cell-specific caspase-3 activation. Interestingly, CAI-diet reduced endothelial and astrocytic Aβ deposits, and Aβ-induced caspase activation. Interestingly, the augmented expression of cerebral TREM2 and CD68 in CAI-treated mice suggests an attenuated inflammatory response, concomitantly with a boost of the cerebral clearance and active Aβ removal from brain microglia/macrophages, respectively, which may underlie the observed Aβ reduction. Furthermore, preliminary data suggest that both ATZ and MTZ promote microglial endocytosis, possibly facilitating Aβ degradation.CAIs provide neuroprotection, fostering neurovascular and glial physiological functions and clearance mechanisms, and attenuating CVD.