Hepatic HIF-1 stabilization increases retinal and brain serine/1-carbon metabolism

Abstract

Purpose : Stabilization of hepatic hypoxia inducible factor-1 (HIF-1) by dimethyl oxaloylglycine (DMOG) protects both retina and brain from oxygen induced retinopathy (OIR) and oxygen induced periventricular leukomalacia (OPVL), respectively. We have previously demonstrated that hepatic HIF-1 stabilization upregulates serine/1-carbon metabolism (serine/1CM) and that this pathway is essential to HIF induced protection against OIR. In this study, we measured the metabolism of [U-¹³C₃] serine in liver and brain extracts from mouse pups with and without DMOG induced hepatic HIF-1 stabilization.

Methods : C57BL/6J mouse pups were injected with 0.9% NaCl or DMOG 200 μg/g bodyweight intraperitoneally (IP) on P3, P5, and P7. After the third injection, pups were fasted for 4 hrs then injected IP with 80 μL [U-¹³C₃] serine (10 mg/ml), and 1 hr later, brain and liver samples were dissected and snap-frozen. Metabolites were extracted by methanol/chloroform/water and were assayed using gas chromatography mass spectrometry.

Results : DMOG treatment induced a 2-fold increase in both relative abundance and fractional enrichments of M3 serine and M2 glycine in liver. In brain, DMOG treatment increased the fractional enrichment of M3 serine 2.5-fold with no statistiscally significant increase in relative abundance. Brain glycine increased by 50% whereas fractional enrichment increases of M2 glycine was statistically insignificant in brain. There was a trend toward increased M2 hypotaurine in both brain and liver, but hypotaurine levels were decreased in both tissues under DMOG stimulus. Taurine levels were unchanged in both tissues with and without DMOG treatment. M3 Lactate:pyruvate ratios were stable and close to 1.0 in all conditions.

Conclusions : These data demonstrate that exogenous serine (and hence liver derived serine) is able to cross the blood-brain barrier as would be expected for neutral amino acids via their respective carriers. However, DMOG induced increases in M2 hepatic down-stream metabolites of serine/1CM such as M2 glycine in both brain and liver suggesting that hepatic HIF-1 stabilization provides 1C metabolites for brain via liver derived serine, at least in neonatal mouse pups at P7. Serine is a key component of myelin, necessary to glycosphingolipid synthesis, providing a potential mechanism for how hepatic stabilization of HIF-1 (remote protection) could increase CNS myelination.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.