Membrane-bound O-acyltransferase 7 (MBOAT7) shapes lysosomal lipid homeostasis and function to control alcohol-associated liver injury.

Recent genome-wide association studies (GWAS) have identified a link between single-nucleotide polymorphisms (SNPs) near the MBOAT7 gene and advanced liver diseases. Specifically, the common MBOAT7 variant (rs641738) associated with reduced MBOAT7 expression is implicated in non-alcoholic fatty liver disease (NAFLD), alcohol-associated liver disease (ALD), and liver fibrosis. However, the precise mechanism underlying MBOAT7-driven liver disease progression remains elusive. Previously, we identified MBOAT7-driven acylation of lysophosphatidylinositol lipids as key mechanism suppressing the progression of NAFLD (Gwag et al., 2019). Here, we show that MBOAT7 loss of function promotes ALD via reorganization of lysosomal lipid homeostasis. Circulating levels of MBOAT7 metabolic products are significantly reduced in heavy drinkers compared to healthy controls. Hepatocyte- (Mboat7-HSKO), but not myeloid-specific (Mboat7-MSKO), deletion of Mboat7 exacerbates ethanol-induced liver injury. Lipidomic profiling reveals a reorganization of the hepatic lipidome in Mboat7-HSKO mice, characterized by increased endosomal/lysosomal lipids. Ethanol-exposed Mboat7-HSKO mice exhibit dysregulated autophagic flux and lysosomal biogenesis, associated with impaired transcription factor EB-mediated lysosomal biogenesis and autophagosome accumulation. This study provides mechanistic insights into how MBOAT7 influences ALD progression through dysregulation of lysosomal biogenesis and autophagic flux, highlighting hepatocyte-specific MBOAT7 loss as a key driver of ethanol-induced liver injury.

Membrane Bound O-Acyltransferase 7 (MBOAT7) Shapes Lysosomal Lipid Homeostasis and Function to Control Alcohol-Associated Liver Injury.

Several recent genome-wide association studies (GWAS) have identified single nucleotide polymorphism (SNPs) near the gene encoding membrane-bound O -acyltransferase 7 ( MBOAT7 ) that is associated with advanced liver diseases. In fact, a common MBOAT7 variant (rs641738), which is associated with reduced MBOAT7 expression, confers increased susceptibility to non-alcoholic fatty liver disease (NAFLD), alcohol-associated liver disease (ALD), and liver fibrosis in those chronically infected with hepatitis viruses B and C. The MBOAT7 gene encodes a lysophosphatidylinositol (LPI) acyltransferase enzyme that produces the most abundant form of phosphatidylinositol 38:4 (PI 18:0/20:4). Although these recent genetic studies clearly implicate MBOAT7 function in liver disease progression, the mechanism(s) by which MBOAT7-driven LPI acylation regulates liver disease is currently unknown. Previously we showed that antisense oligonucleotide (ASO)-mediated knockdown of Mboat7 promoted non-alcoholic fatty liver disease (NAFLD) in mice (Helsley et al., 2019). Here, we provide mechanistic insights into how MBOAT7 loss of function promotes alcohol-associated liver disease (ALD). In agreement with GWAS studies, we find that circulating levels of metabolic product of MBOAT7 (PI 38:4) are significantly reduced in heavy drinkers compared to age-matched healthy controls. Hepatocyte specific genetic deletion ( Mboat7 HSKO ), but not myeloid-specific deletion ( Mboat7 MSKO ), of Mboat7 in mice results in enhanced ethanol-induced hepatic steatosis and high concentrations of plasma alanine aminotransferase (ALT). Given MBOAT7 is a lipid metabolic enzyme, we performed comprehensive lipidomic profiling of the liver and identified a striking reorganization of the hepatic lipidome upon ethanol feeding in Mboat7 HSKO mice. Specifically, we observed large increases in the levels of endosomal/lysosomal lipids including bis(monoacylglycero)phosphates (BMP) and phosphatidylglycerols (PGs) in ethanol-exposed Mboat7 HSKO mice. In parallel, ethanol-fed Mboat7 HSKO mice exhibited marked dysregulation of autophagic flux and lysosomal biogenesis when exposed to ethanol. This was associated with impaired transcription factor EB (TFEB)-mediated lysosomal biogenesis and accumulation of autophagosomes. Collectively, this works provides new molecular insights into how genetic variation in MBOAT7 impacts ALD progression in humans and mice. This work is the first to causally link MBOAT7 loss of function in hepatocytes, but not myeloid cells, to ethanol-induced liver injury via dysregulation of lysosomal biogenesis and autophagic flux.

Modulation of hepatic transcription factor EB activity during cold exposure uncovers direct regulation of bis(monoacylglycero)phosphate lipids by Pla2g15.

Cold exposure is an environmental stress that elicits a rapid metabolic shift in endotherms and is required for survival. The liver provides metabolic flexibility through its ability to rewire lipid metabolism to respond to an increased demand in energy for thermogenesis. We leveraged cold exposure to identify novel lipids contributing to energy homeostasis and found that lysosomal bis(monoacylglycero)phosphate (BMP) lipids were significantly increased in the liver during acute cold exposure. BMP lipid changes occurred independently of lysosomal abundance but were dependent on the lysosomal transcriptional regulator transcription factor EB (TFEB). Knockdown of TFEB in hepatocytes decreased BMP lipid levels. Through molecular biology and biochemical assays, we found that TFEB regulates lipid catabolism during cold exposure and that TFEB knockdown mice were cold intolerant. To identify how TFEB regulates BMP lipid levels, we used a combinatorial approach to identify TFEB target Pla2g15 , a lysosomal phospholipase, as capable of degrading BMP lipids in in vitro liposome assays. Knockdown of Pla2g15 in hepatocytes led to a decrease in BMP lipid species. Together, our studies uncover a required role of TFEB in mediating lipid liver remodeling during cold exposure and identified Pla2g15 as an enzyme that regulates BMP lipid catabolism.

Protein restriction slows the development and progression of Alzheimer's disease in mice.

Over the last decade, it has become evident that dietary protein is a critical regulator of metabolic health and aging. Low protein diets are associated with healthy aging in humans, and we and others have shown that dietary protein restriction (PR) extends the lifespan and healthspan of mice. Here, we examined the effect of PR on metabolic health and the development and progression of Alzheimer's disease (AD) in the 3xTg mouse model of AD. We found that PR has metabolic benefits for 3xTg mice and non-transgenic controls of both sexes, promoting leanness and glycemic control in 3xTg mice. We found that PR induces sex-specific alterations in circulating metabolites and in the brain lipidome, downregulating sphingolipid subclasses including ceramides, glucosylceramides, and sphingomyelins in 3xTg females. Consumption of a PR diet starting at 6 months of age reduced AD pathology in conjunction with reduced mTORC1 activity, increased autophagy, and had cognitive benefits for 3xTg mice. Finally, PR improved the survival of 3xTg mice. Our results demonstrate that PR slows the progression of AD at molecular and pathological levels, preserves cognition in this mouse model of AD, and suggests that PR or pharmaceutical interventions that mimic the effects of this diet may hold promise as a treatment for AD.

Quantifying In Situ Structural Stabilities of Human Blood Plasma Proteins Using a Novel Iodination Protein Stability Assay.

Many of the diseases that plague society today are driven by a loss of protein quality. One method to quantify protein quality is to measure the protein folding stability (PFS). Here, we present a novel mass spectrometry (MS)-based approach for PFS measurement, iodination protein stability assay (IPSA). IPSA quantifies the PFS by tracking the surface-accessibility differences of tyrosine, histidine, methionine, and cysteine under denaturing conditions. Relative to current methods, IPSA increases protein coverage and granularity to track the PFS changes of a protein along its sequence. To our knowledge, this study is the first time the PFS of human serum proteins has been measured in the context of the blood serum (in situ). We show that IPSA can quantify the PFS differences between different transferrin iron-binding states in near in vivo conditions. We also show that the direction of the denaturation curve reflects the in vivo surface accessibility of the amino acid residue and reproducibly reports a residue-specific PFS. Along with IPSA, we introduce an analysis tool Chalf that provides a simple workflow to calculate the residue-specific PFS. The introduction of IPSA increases the potential to use protein structural stability as a structural quality metric in understanding the etiology and progression of human disease. Data is openly available at Chorusproject.org (project ID 1771).

Proposing a minimal set of metrics and methods to predict probabilities of amyloidosis disease and onset age in individuals.

Many amyloid-driven pathologies have both genetic and stochastic components where assessing risk of disease development requires a multifactorial assessment where many of the variables are poorly understood. Risk of transthyretin-mediated amyloidosis is enhanced by age and mutation of the transthyretin (TTR) gene, but amyloidosis is not directly initiated by mutated TTR proteins. Nearly all of the 150+ known mutations increase dissociation of the homotetrameric protein structure and increase the probability of an individual developing a TTR amyloid disease late in life. TTR amyloidosis is caused by dissociated monomers that are destabilized and refold into an amyloidogenic form. Therefore, monomer concentration, monomer proteolysis rate, and structural stability are key variables that may determine the rate of development of amyloidosis. Here we develop a unifying biophysical model that quantifies the relationships among these variables in plasma and suggest the probability of an individual developing a TTR amyloid disease can be estimated. This may allow quantification of risk for amyloidosis and provide the information necessary for development of methods for early diagnosis and prevention. Given the similar observation of genetic and sporadic amyloidoses for other diseases, this model and the measurements to assess risk may be applicable to more proteins than just TTR.