Proximal Tubular Cholesterol Loading following Mitochondrial, but Not Glycolytic, Blockade

Background: Diverse forms of injury cause proximal tubular cholesterol accumulation. However, underlying mechanisms, in general, and those involved with ATP depletion injury, in particular, remain poorly defined. To help elucidate this issue, cholesterol homeostasis and its determinants were assessed following partial ATP depletion states. Methods: Serumexposed HK-2 cells were subjected to mild ATP depletion, induced by mitochondrial inhibition (antimycin A; AA) or glycolytic blockade (2-deoxyglucose; DG). Four or 18 hrs later, cell cholesterol levels, HMG CoA reductase (HMGCR), the LDL receptor (LDL-R), and the ABCA1/SR-B1 cholesterol transporters were assessed. Results. AA and DG each induced mild, largely sublethal ATP depletion injury. Each also caused significant HMGCR increments and SR-B1 decrements, and left ABCA1 intact. In contrast, only AA increased the LDL-R, and only AA evoked a cholesterol loading state (~25% ↑). Half of this increase was statin inhibitable, and half could be blocked by serum deletion, implying that both synthetic and non synthetic (e.g., LDL-R transport) pathways were involved. The AA-induced HMGCR and LDL-R protein changes were paralleled by their mRNAs, suggesting the presence of altered transcriptional events. Conclusions: 1) Sublethal ATP depletion, whether induced by mitochondrial or glycolytic blockade, can upregulate HMGCR and decrease SR-B1. These changes represent a previously unrecognized ATP depletion 'phenotype'. 2) Mitochondrial blockade can also upregulate the LDL-R and evoke a cholesterol loading state. 3) The latter likely occurs via synthetic and transport pathways; and 4) the mitochondrion may be a critical, and previously unrecognized, determinant of post injurycell cholesterol homeostasis, potentially by impacting the LDL-R.