HMGCR Pathway Mediates Cerebral-Vascular Stability and Angiogenesis in Developing Zebrafish.

Intracerebral hemorrhage (ICH) is a severe form of stroke, with a high mortality rate and often resulting in irreversible neurological deterioration. Although animal studies have provided insight into the etiology of the disease, many of the causative genes and mechanisms implicated in cerebral-vascular malformations are unknown. Treatment options remain ineffective. With the present models, the pathophysiological consequences of ICH can only be assessed in situ and after histological analysis. Furthermore, common deficiencies of the current models include the heterogeneity, low expression and low reproducibility of the desired phenotype. Hence, there is a requirement for novel approaches to model ICH pathogenesis. Zebrafish (Danio rerio) has gained recognition as a vertebrate model for stroke research. Through a combination of pharmacological blockers, metabolite rescue, genetic approaches, and confocal imaging analysis, I demonstrate a requirement for the 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) pathway in regulating developmental cerebral-vascular stabilization. A transient loss in HMGCR function induces ICH, characterised by progressive dilation of blood vessels, vascular permeability and vessel rupture. These effects are likely due to reduced prenylation of Rho GTPases, evidenced by morpholino-mediated blocking of the prenylation pathway and in vivo assessment of endothelial-specific localization of cdc42, a Rho GTPase family protein. These results are in conformity with recent clinical and experimental evidence. I have further shown that this model consistently replicates common pathoghysiological processes associated with ICH. The hemorrhages are associated with the disruption of the blood-brain barrier, vessel disintegration, hematoma expansion and edema into the adjacent brain regions. Also, enhanced apoptosis, activation of inflammatory mediators in the periphery of the hematoma, enriched heme oxygenase 1 (HO-1) expression and localised thrombosis were observed in these embryos. I show that the patterning and distribution of catecholaminergic neurons, response to sensory stimulus and swimming speed were impaired as a consequence of ICH. These results suggest that HMGCR contributes to cerebral-vascular stabilisation through Rho GTPase mediated-signalling and that zebrafish can serve as a powerful paradigm for the systemic analysis of the etiological and pathophysiological underpinnings of ICH and can help establish the basis for future studies into screening for putative therapeutics and elucidating mechanisms aiding functional recovery.