Hypoxia-inducible factor (HIF) mediates protection via hypoxic preconditioning in both, in vitro and in vivo
ischemia models. However, the underlying mechanism remains largely unknown.
Prolyl hydroxylase domain
proteins serve as the main HIF regulator via hydroxylation of HIFα leading to its degradation. At present,
prolyl hydroxylase inhibitors including
enarodustat are under clinical trials for the treatment of renal
anemia. In an in vitro model of
ischemia produced by
oxygen-
glucose deprivation of renal proximal tubule cells in culture,
enarodustat treatment and
siRNA knockdown of
prolyl hydroxylase 2, but not of
prolyl hydroxylase 1 or
prolyl hydroxylase 3, significantly increased the cell viability and reduced the levels of
reactive oxygen species. These effects were offset by the simultaneous knockdown of HIF1α. In another in vitro
ischemia model induced by the blockade of oxidative phosphorylation with
rotenone/
antimycin A,
enarodustat-enhanced
glycogen storage prolonged glycolysis and delayed
ATP depletion. Although autophagy is another possible mechanism of
prolyl hydroxylase inhibition-induced cytoprotection, gene knockout of a key autophagy associated
protein, Atg5, did not affect the protection.
Enarodustat increased the expression of several
enzymes involved in
glycogen synthesis, including
phosphoglucomutase 1,
glycogen synthase 1, and 1,4-α
glucan branching enzyme. Increased
glycogen served as substrate for
ATP and
NADP production and augmented reduction of
glutathione. Inhibition of
glycogen synthase 1 and
glutathione reductase nullified
enarodustat's protective effect.
Enarodustat also protected the kidneys in a rat
ischemia reperfusion injury model and the protection was partially abrogated by inhibiting glycogenolysis. Thus,
prolyl hydroxylase inhibition protects the kidney from
ischemia via upregulation of
glycogen synthesis.