Biology subjects

Smith, G. I.

Publications and source records attributed to Smith, G. I..

7 recordsLinked to original sources

bioRxiv2026

Proteome-wide QTL mapping enables gene-protein-phenotype metabolic network construction in a genetically diverse MASLD mouse model

The limited treatment options available for the estimated 38% of adults worldwide affected by Metabolic Dysfunction Associated Steatotic Liver Disease (MASLD) are largely due to an incomplete understanding of the complex molecular networks underlying disease pathogenesis. To dissect the genetic architecture and proteomic regulation underlying MASLD, we generated a genetically diverse mouse cohort through a four-way cross of founder strains with varying susceptibility to liver disease, producing 444 F2 mice with a spectrum of phenotypes and genotypes. Utilizing deep proteomic profiling of the livers of this population, we identified quantitative trait loci (QTL) for 2,652 proteins, spanning over 4,000 unique genomic loci, and distinguished cis- and trans-acting regulatory mechanisms. Integrating proteomic, genomic, and phenotypic data reveals key regulatory loci and candidate proteins influencing disease progression, creating a mineable proteogenomic resource for MASLD research. We utilize this resource to identify the E3 ubiquitin ligase Ubr1 as a candidate central regulator connecting proteostasis and lipid metabolism, with genetic polymorphisms that may alter its abundance and predispose to metabolic dysfunction. This study demonstrates how high-throughput, deep proteome profiling integrated with QTL mapping can reveal complex gene-protein networks governing MASLD susceptibility and progression, offering novel insights for biomarker discovery and therapeutic targeting.

systems biology↗

bioRxiv2026

Adipocyte Expression of O-Glycoprotein Procollagen C-Endopeptidase Enhancer Protein 2 (PCPE2): Mechanisms Linking Fibrosis and Beiging of White Adipose Tissue

BackgroundProcollagen C-endopeptidase enhancer protein 2 (Pcpe2) has been primarily investigated in collagen processing during wound healing and is assumed to function similarly to Pcpe1 in the extracellular matrix (ECM). Our studies suggest that Pcpe2 has unique structural and functional features not shared with Pcpe1. MethodsTo study the role of Pcpe2 in adipose tissue remodeling, we created adipose tissue-specific knockout of Pcpe2 (TgAd+Pcpe2KO) and adipose tissue-specific Pcpe2 overexpressing (TgAd+Pcpe2Ox) mice and performed in vivo and ex vivo experiments. ResultsWe show that TgAd+Pcpe2KO mice are resistant to WD-induced obesity and exhibit reductions in body and fat pad mass. Promethion cage studies showed no significant differences in lean mass or food intake, yet WD-fed TgAd+Pcpe2KO mice exhibited significantly higher energy expenditure than negative Cre littermate controls. WD-fed TgAd+Pcpe2KO mice also showed reduced plasma glucose and lipoprotein lipid concentrations compared to controls. While markers of adipose tissue inflammation were reduced in WD-fed TgAd+Pcpe2KO mice. Examination of mature adipocytes from white adipose tissue showed that WD consumption greatly stimulated Pcpe2 expression, while no change in Pcpe2 expression in the stromal vascular cells was noted. However, in VAT precursor cells (PCs), the CD140b+ population showed a shift from fibroadipogenic precursors towards adipocyte PCs in TgAd+Pcpe2KO mice. This shift in PCs may account for the attenuation of local inflammation and fibrosis in the absence of Pcpe2. Ex vivo differentiation of adipose PCs showed that loss of Pcpe2 enhanced adipocyte differentiation, reducing TGF{beta}-like signaling via pSmad2/3, and increasing mitochondrial function. Furthermore, unlike Pcpe1, Pcpe2 contains a mucin-like linker domain with nine sites of O-linked glycosylation which may regulate receptor signaling at the plasma membrane. ConclusionsOur results show the ECM O-glycoprotein Pcpe2 is a robust marker of unhealthy adipose tissue expansion in humans and mice and contributes to inflammation and fibrosis associated with WD-induced obesity.

cell biology↗

bioRxiv2025

Immune cells regulate circulating adipocyte extracellular vesicle levels in response to metabolic shifts

Extracellular vesicles (EVs) are now recognized as potent mediators of intercellular and inter-organ signaling and implicated in the pathogenesis of obesity and its associated comorbidities such as diabetes, cancer, cardiovascular disease, and neurodegeneration. Despite a surge of new functional information about EVs, we still lack a basic understanding of how endogenous EV levels are controlled to regulate inter-organ signaling. New flow cytometry technology has allowed us to study the regulation of circulating, endogenous EVs from metabolically relevant cell types like adipocytes. From this, we provide evidence for a paradigm of EV regulation where tissue resident immune cells, predominantly macrophages, clear EVs released by local tissue cells or EVs entering the tissue from circulation, an activity that determines circulating EV levels. In obesity, EV uptake by adipose tissue immune cells is reduced, concomitant with increased circulating adipocyte-specific EVs (adipoEVs) and reduced EV clearance rates. AdipoEVs are significantly elevated in mouse circulation from one day to 20 weeks of high-fat feeding. In humans we found that adipocyte EV levels negatively correlate with whole-body and liver insulin sensitivity and are not associated with adipose mass. This work suggests that tissue resident immune cells act as a gatekeeper for tissue EV entry into circulation and are thereby a major regulator of inter-organ EV signaling.

physiology↗

bioRxiv2025

Isotope tracing-based metabolite identificationfor mass spectrometry metabolomics

Modern mass spectrometry-based metabolomics is a key technology for biomedicine, enabling discovery and quantification of a wide array of biomolecules critical for human physiology. Yet, only a fraction of human metabolites have been structurally determined, and the majority of features in typical metabolomics data remain unknown. To date, metabolite identification relies largely on comparing MS2 fragmentation patterns against known standards, related compounds or predicted spectra. Here, we propose an orthogonal approach to identification of endogenous metabolites, based on mass isotopomer distributions (MIDs) measured in an isotope-labeled reference material. We introduce a computational measure of pairwise distance between metabolite MIDs that allows identifying novel metabolites by their similarity to previously known peaks. Using cell material labeled with 20 individual 13C tracers, this method identified 62% of all unknown peaks, including previously never seen metabolites. Importantly, MID-based identification is highly complementary to MS2-based methods in that MIDs reflect the biochemical origin of metabolites, and therefore also yields insight into their synthesis pathways, while MS2 spectra mainly reflect structural features. Accordingly, our method performed best for small molecules, while MS2-based identification was stronger on lipids and complex natural products. Among the metabolites discovered was trimethylglycyl-lysine, a novel amino acid derivative that is altered in human muscle tissue after intensive lifestyle treatment. MID-based annotation using isotope-labeled reference materials enables identification of novel endogenous metabolites, extending the reach of mass spectrometry-based metabolomics.

biochemistry↗

bioRxiv2024

MXRA8 promotes adipose tissue whitening to drive obesity

Matrix-remodeling associated 8 (MXRA8), also known as Dual immunoglobulin domain cell adhesion molecule (DICAM), is a type 1 transmembrane protein that reportedly binds the V{beta}3 integrin1 and regulates the differentiation of osteoclasts2 and chondrocytes3, tumor growth4, T cell trafficking5, and angiogenesis6. MXRA8 is also an essential entry receptor for chikungunya virus and other related arthritogenic alphaviruses.7-9 We compared MXRA8 expression in 51 tissues in the Human Protein Atlas and found it is most highly expressed in white adipose tissue (WAT), however the function of MXRA8 in WAT is unknown. Here, we found that MXRA8 expression in WAT is increased in people with obesity and that this response is also observed in a mouse model of high fat-diet (HFD)-induced obesity. Single-nucleus RNA sequencing and high-dimensional spectral flow cytometry analyses revealed that MXRA8 is expressed predominantly by adipocyte progenitor (AP) cells and mature adipocytes. MXRA8 mutant primary adipocytes from inguinal (i)WAT exhibited increased expression of Uncoupling protein 1 (UCP1), a thermogenic protein expressed by beige and brown adipocytes that limits obesity pathogenesis.10-12 Indeed, MXRA8 mutant mice fed a HFD had preserved UCP1+ beige and brown adipocytes and were protected from HFD-induced obesity in a UCP1-dependent manner. Collectively, these findings indicate that MXRA8 promotes whitening of beige and brown adipose tissues to drive obesity pathogenesis and identify MXRA8 as a possible therapeutic target to treat obesity and associated metabolic diseases.

physiology↗

bioRxiv2023

Adipocyte lipin 1 is positively associated with metabolic health in humans and regulates systemic metabolism in mice.

Dysfunctional adipose tissue is believed to promote the development of hepatic steatosis and systemic insulin resistance, but many of the mechanisms involved are still unclear. Lipin 1 catalyzes the conversion of phosphatidic acid to diacylglycerol (DAG), the penultimate step of triglyceride synthesis, which is essential for lipid storage. Herein we found that adipose tissue LPIN1 expression is decreased in people with obesity compared to lean subjects and low LPIN1 expression correlated with multi-tissue insulin resistance and increased rates of hepatic de novo lipogenesis. Comprehensive metabolic and multi-omic phenotyping demonstrated that adipocyte-specific Lpin1-/- mice had a metabolically-unhealthy phenotype, including liver and skeletal muscle insulin resistance, hepatic steatosis, increased hepatic de novo lipogenesis, and transcriptomic signatures of nonalcoholic steatohepatitis that was exacerbated by high-fat diets. We conclude that adipocyte lipin 1-mediated lipid storage is vital for preserving adipose tissue and systemic metabolic health and its loss predisposes mice to nonalcoholic steatohepatitis.

physiology↗

bioRxiv2021

Silencing alanine transaminase 2 in diabetic liver attenuates hyperglycemia by reducing gluconeogenesis from amino acids

Hepatic gluconeogenesis from amino acids contributes significantly to diabetic hyperglycemia, but the molecular mechanisms involved are incompletely understood. Alanine transaminases (ALT1 and ALT2) catalyze the interconversion of alanine and pyruvate, which is required for gluconeogenesis from alanine. We found that ALT2 was overexpressed in liver of diet-induced obese and db/db mice and that the expression of the gene encoding ALT2 (GPT2) was downregulated following bariatric surgery in people with obesity. The increased hepatic expression of Gpt2 in db/db liver was mediated by activating transcription factor 4; an endoplasmic reticulum stress-activated transcription factor. Hepatocyte-specific knockout of Gpt2 attenuated incorporation of 13C-alanine into newly synthesized glucose by hepatocytes. In vivo Gpt2 knockdown or knockout in liver had no effect on glucose concentrations in lean mice, but Gpt2 suppression alleviated hyperglycemia in db/db mice. These data suggest that ALT2 plays a significant role in hepatic gluconeogenesis from amino acids in diabetes.

physiology↗