Metabolic and Epigenetic Perspective of Cholesterol and Caveolin-1 in Glioblastoma: Inhibition of Cholesterol Biosynthesis Hampers HH Signaling

Abstract

Glioblastoma is one of the most aggressive gliomas with poor survival rate and limited treatment strategies which mostly lead to relapse. Conventional therapies fail to overcome cancer recurrence due to the existence of stem cell like CSCs. Eradicating cancer stem cells may provide improved treatment alternatives. For in vivo characterization and better insight into unique properties of cancer stem cells (CSCs), by using hanging drop method, we developed glioblastoma spheres that were enriched with glioblastoma stem like cells, having higher expression of stem cell markers; CD133, CD44, and pax6. As increasing evidences suggest glioblastoma stem cells rewire cholesterol metabolism to support self-renewal and stem cell maintenance, we have inhibited cholesterol biosynthesis by lovastatin, and reduced caveolin-1 expression by siRNA treatment. By challenging GSC spheres with chemical inhibitor towards cholesterol biosynthetic pathway (lovastatin), stemness was reduced and increase in differentiation was noted by the expression of S100B. Further, from CAV1-KD studies, we understood that CAV1 protein is essential for cholesterol homeostasis and maintenance of stemness, as the expression of cholesterol biosynthetic genes - HMGCR1 and DHCR24 and stemness markers were reduced when GSC spheres were treated with CAV1-siRNA. As lovastatin treatment enhanced KDM5A levels, which could reduce H3K4me3 levels on target genes leading to their suppression, we tested if caveolin-1 was a KDM5A target. From our ChIP experiments, we indeed observed that KDM5A mediated reduction of H3K4me3 occurs on cav1 promoter following lovastatin treatment. Through this study, we have proved that cholesterol inhibition by lovastatin enhances KDM5A expression leading to decreased stemness and metabolic deprivation by caveolin-1 downregulation. Cellular cholesterol and Cav1 associated signalling could be one of the promising targets for GSCs management.