The role of ethanolamine phosphate phospholyase in regulation of astrocyte lipid homeostasis

Cory J White,Jessica M Ellis,Michael J Wolfgang

doi:10.1016/j.jbc.2021.100830

Abstract

Dietary lipid composition has been shown to impact brain morphology, brain development, and neurologic function. However, how diet uniquely regulates brain lipid homeostasis compared with lipid homeostasis in peripheral tissues remains largely uncharacterized. To evaluate the lipid response to dietary changes in the brain, we assessed actively translating mRNAs in astrocytes and neurons across multiple diets. From this data, ethanolamine phosphate phospholyase (Etnppl) was identified as an astrocyte-specific fasting-induced gene. Etnppl catabolizes phosphoethanolamine (PEtN), a prominent headgroup precursor in phosphatidylethanolamine (PE) also found in other classes of neurologically relevant lipid species. Altered Etnppl expression has also previously been associated with humans with mood disorders. We evaluated the relevance of Etnppl in maintaining brain lipid homeostasis by characterizing Etnppl across development and in coregulation with PEtN-relevant genes, as well as determining the impact to the brain lipidome after Etnppl loss. We found that Etnppl expression dramatically increased during a critical window of early brain development in mice and was also induced by glucocorticoids. Using a constitutive knockout of Etnppl (EtnpplKO), we did not observe robust changes in expression of PEtN-related genes. However, loss of Etnppl altered the phospholipid profile in the brain, resulting in increased total abundance of PE and in polyunsaturated fatty acids within PE and phosphatidylcholine species in the brain. Together, these data suggest that brain phospholipids are regulated by the phospholyase action of the enzyme Etnppl, which is induced by dietary fasting in astrocytes.

Highlights

Dietary lipid composition has been shown to impact brain morphology, brain development, and neurologic function
ethanolamine phosphate phospholyase (Etnppl) is regulated by fasting in central nervous system (CNS) astrocytes
To assess how gene expression in the brain is altered in situ by nutritional cues, we performed translating ribosomal affinity purification (TRAP) [40] in several cell types in the CNS upon nutritional modulation

Summary

Results

Neurological disorders, including epileptic seizures, often exhibit improved outcomes with fasting or ketogenic diets. Samples from astrocyte-specific TRAP mice were further used for whole exome microarray analysis (Fig. S1). The induction of Etnppl in astrocytes upon fasting was validated using quantitative real-time polymerase chain reaction (qRT-PCR) with hippocampal astrocyte- and neuronspecific samples across chow, ketogenic, and fasted diets from input (total RNA) and immunoprecipitated fractions from TRAP mice. We confirmed that the induction of Etnppl is astrocyte-specific with no induction in neuron-specific IPs (Fig. 1B) Consistent with these observations, hippocampal Etnppl protein, determined using a C-terminal directed Etnppl antibody developed by our laboratory, was induced by fasting (Fig. 1C). When examining the mRNA expression across regions of the brain including cortex, hippocampus, and cerebellum, we observed that Etnppl was highly developmentally regulated postnatally (Fig. 1D).

30 Cortex

Discussion

Experimantal procedures