Sterol metabolism regulates clathrin-mediated endocytosis and intracellular trafficking within isogenic stem cell models.

Clathrin-mediated endocytosis (CME) is a critical cellular pathway for regulation of intracellular signaling, vesicular recycling, and receptor sensitization. While CME is a molecularly complex process which was previously shown to be inhibited by cholesterol depletion, the precise impact of sterol metabolism on CME, the cellular mechanisms involved, and the relevance to disease pathology remain unclear. To determine the impact of sterol homeostasis on CME and possible roles for CME within diseases impacted by cholesterol metabolism, CRISPR/Cas9 gene editing was utilized to fluorescently label clathrin light chain A and dynamin 2 in both immortalized and induced pluripotent stem cell (iPSC) models. To model how cholesterol levels and disease-relevant sterol changes observed in cholesterol biosynthetic disorders (characterized by the substitution of cellular cholesterol for sterol intermediates) impact endocytosis, CME was analyzed under varying biochemical states. Live cell imaging demonstrated clathrin immobilization at the cell membrane and functional CME impairment occurred following either cholesterol depletion or upon accumulation of sterol species incapable of supporting ordered lipid domains. Polarized total internal reflection fluorescence microscopy demonstrated prolonged clathrin lifetimes associated with endocytic pits with variable curvature in correlation with sterol abundance and support of phase separation. To address the impact of sterol-mediated CME on neurodevelopment, human iPSCs were analyzed at various stages of differentiation for trafficking deficits following sterol depletion or cholesterol metabolism disruption. CME deficits in iPSCs preceded loss of pluripotency, morphological changes, or aberrant differentiation events observed following cholesterol depletion or sterol intermediate accumulation. CME deficits were also cell-stage specific, CME activity corresponded to the rate of intracellular sterol metabolism, and organellar deficits with disease relevance resulted from CME deficiencies. Ongoing studies are investigating the consequences of sterol depletion and sterol substitution on developmental signaling pathways and cellular function to provide insight into the mechanistic requirements for sterol homeostasis in CME-mediated cellular trafficking.