Hydrogen sulfide accumulates LDL receptor precursor via downregulating PCSK9 in HepG2 cells

Endogenous hydrogen sulfide (H2S) affects cholesterol homeostasis and liver X receptor alpha (LXR alpha) expression. However, whether low-density lipoprotein (LDL) receptor (LDLR), a key player in cholesterol homeostasis, is regulated by exogenous H2S through LXR alpha signaling has not been determined. We investigated the effects of sodium hydrosulfide (NaHS, H2S donor) on LDLR expression in the presence or absence of LXR agonists, T0901317 or GW3965 in HepG2 cells. We found that H2S strongly accumulated LDLR precursor in the presence of T0901317. Hence, LDLR transcription and the genes involved in LDLR precursor maturation and degradation were studied. T0901317 increased the LDLR mRNA level, whereas H2S did not affect LDLR transcription. H2S had no significant effect on the expression of LXR alpha and inducible degrader of LDLR (IDOL). H2S and T0901317 altered mRNA levels of several enzymes for N- and O-glycosylation and endoplasmic reticulum (ER) chaperones assisting LDLR maturation, but did not affect their protein levels. H2S decreased proprotein convertase subtilisin/kexin type 9 (PCSK9) protein levels and its mRNA level elevated by T0901317. T0901317 with PCSK9 siRNA also accumulated LDLR precursor as did T0901317 with H2S. High glucose increased PCSK9 protein levels and attenuated LDLR precursor accumulation induced by T0901317 with H2S. Taken together, H2S accumulates LDLR precursor by downregulating PCSK9 expression but not through the LXR alpha-IDOL pathway, LDLR transcriptional activation, or dysfunction of glycosylation enzymes and ER chaperones. These results also indicate that PCSK9 plays an important role in LDLR maturation in addition to its well-known effect on the degradation of LDLR mature form.