A novel gene edited rat model of cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL).

Background: Cerebral Autosomal Recessive Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CARASIL) is a rare hereditary cerebral small vessel disease associated with loss-of-function mutations in the High Temperature Requirement Serine Protease 1 (HTRA1). While previous mouse models have provided insight into the functions of HTRA1, they have incompletely replicated the pathogenesis of CARASIL. Methods: A novel gene-edited rat model of CARASIL (designated CRHTRA1) was generated containing the loss-of-function Htra1 mutation p.R302Q. Quantitative cognitive, physiological, pathological and transcriptomic analyses were conducted to assess the CARASIL phenotype. Results: At 12 months, histopathological analyses revealed marked thickening of the cerebral arteriolar walls with concomitant lumen stenosis. Changes in elastic composition, vascular smooth muscle cells and extracellular matrix proteins were identified in cerebral arteries. Downstream pathological remodeling of vasculature is implicated in increased capillary tortuosity and changes in capillary coverage in specific brain regions. Focal hyperintensity regions associated with enlarged perivascular spaces were identified locally by in vivo proton density weighted MRI. Region-specific reductions of fractional anisotropy were identified using diffusion tensor imaging and correlated with a reduction in neuronal densities. Behavioral testing in CRHTRA1 rats revealed significant cognitive deficit and gait disturbances. Micro-computed tomography of spinal vertebrae revealed pronounced increases in osteophyte formation. Global cerebral RNA sequencing revealed changes in signaling pathways associated with the loss-of-function HTRA1 CARASIL mutation, including those associated with transforming growth factor-β signaling and extracellular matrix remodeling. Conclusion: The CRHTRA1 rat recapitulates many pathological changes that are consistent with both clinical CARASIL pathology and studies of HTRA1 function in vitro.