Which factors inhibit HMG-CoA reductase?

HMG-CoA reductase is a key enzyme in the cholesterol biosynthesis pathway and is regulated by various factors. The correct answer includes glucagon, oxysterol, and AMPK, which are known to inhibit the activity of HMG-CoA reductase.

Glucagon acts primarily in the fasted state, signaling the body to mobilize energy and reduce cholesterol synthesis. It does this by promoting the phosphorylation of HMG-CoA reductase through AMPK activation, leading to its inactivation.

Oxysterols are cholesterol derivatives that also serve as feedback regulators in cholesterol homeostasis. High levels of oxysterols signal that there is enough cholesterol present in the cells, thereby inhibiting HMG-CoA reductase to prevent further cholesterol synthesis.

AMPK (AMP-activated protein kinase) is activated during conditions of energy deficiency (like low glucose levels), and when activated, it phosphorylates HMG-CoA reductase, reducing its activity. This ultimately leads to decreased cholesterol synthesis, conserving cellular energy during times of stress.

The incorrect choices do not accurately reflect the factors that inhibit HMG-CoA reductase or include factors that are unrelated to its inhibition. For instance, insulin typically promotes cholesterol synthesis, while factors like testosterone are not directly