Biology subjects

Giacometti, S.

Publications and source records attributed to Giacometti, S..

4 recordsLinked to original sources

bioRxiv2025

CD300e Controls Macrophage Lipid Handling and Safeguards Adipose Tissue Function in Obesity

Previous studies in monozygotic twins discordant for body mass index (BMI) revealed that obese individuals exhibit elevated expression of the immune receptor CD300e in white adipose tissue (WAT). Notably, CD300e levels decreased following weight loss, implicating its involvement in adipose tissue remodeling and metabolic regulation. To elucidate the functional role of CD300e, we employed a Cd300e knockout (Cd300e-/-) mouse model subjected to a high-fat diet (HFD). Our findings demonstrate that CD300e deficiency exacerbates obesity-associated metabolic dysfunction, including increased weight gain, adipocyte hypertrophy, hepatic steatosis, and impaired glucose and insulin sensitivity. Adipose tissue macrophages (ATMs) lacking CD300e displayed reduced lipid and glucose uptake, alongside diminished mitochondrial respiration--a phenotype consistent with a broader metabolic impairment, as evidenced by proteomic profiling. These metabolic deficits were genotype-dependent and persisted after 16 weeks of HFD. Concurrently, adipocytes from Cd300e-/- mice exhibited enhanced lipogenesis and attenuated lipolysis. Remarkably, the impaired metabolic fitness exhibited by Cd300e-/- mouse macrophages was recapitulated in human cells upon gene silencing. Collectively, these results establish CD300e as essential for ATM metabolic activation, positioning it as a key regulator of adipose tissue homeostasis and a critical mediator of obesity-induced metabolic dysfunction. Given its pivotal role, CD300e emerges as a promising therapeutic target for modulating adipose tissue function and improving metabolic health in obesity.

immunology↗

bioRxiv2024

Mechanistic studies of mycobacterial glycolipid biosynthesis by the mannosyltransferase PimE

Tuberculosis (TB), exceeded in mortality only by COVID-19 among global infectious diseases, is caused by Mycobacterium tuberculosis (Mtb). The pathogenicity of Mtb is largely attributed to its complex cell envelope, which includes a class of glycolipids called phosphatidyl-myo-inositol mannosides (PIMs), found uniquely in mycobacteria and its related corynebacterineae. These glycolipids maintain the integrity of the mycobacterial cell envelope, regulate its permeability, and mediate host-pathogen interactions. PIMs consist of a phosphatidyl-myo-inositol core decorated with one to six mannose residues and up to four acyl chains. The mannosyltransferase PimE catalyzes the transfer of the fifth PIM mannose residue from a polyprenyl phosphate-mannose (PPM) donor. This step in the biosynthesis of higher-order PIMs contributes to the proper assembly and function of the mycobacterial cell envelope; however, the structural basis for substrate recognition and the catalytic mechanism of PimE remain poorly understood. Here, we present the cryo-electron microscopy (cryo-EM) structures of PimE from Mycobacterium abscessus captured in its apo form and in a product-bound complex with the reaction product Ac1PIM5 and the by-product polyprenyl phosphate (PP), determined at 3.0 [A] and 3.5 [A], respectively. The structures reveal the active site within a distinctive binding cavity that accommodates both donor and acceptor substrates/products. Within the cavity, we identified residues involved in substrate coordination and catalysis, which we confirmed through in vitro enzymatic assays and further validated by in vivo complementation experiments. Molecular dynamics simulations were applied to identify the access pathways and the dynamics involved in substrate binding. Integrating structural, biochemical, genetic, and computational experiments, our study provides comprehensive insights into how PimE functions, opening potential avenues for development of novel anti-TB therapeutics.

biochemistry↗

bioRxiv2024

CD300e as a Driver of Immunosuppressive Tumor Microenvironment in Colorectal Cancer

Colorectal cancer (CRC) progression is shaped by the tumor microenvironment, particularly tumor-associated macrophages (TAMs), which often adopt immunosuppressive functions. CD300e, a myeloid receptor involved in immune regulation, has an uncharacterized role in CRC. Here, we show that CD300e is selectively upregulated in tumor-infiltrating monocytes and macrophages, driving a suppressive phenotype marked by impaired antigen presentation. In vitro cocultures of patient-derived tumor organoids and human monocytes revealed that tumor-derived signals induce CD300e expression and promote a protumorigenic macrophage profile. Using CD300e knockout mice in AOM/DSS and MC38 CRC models, we found that CD300e loss reduced tumor burden, enhanced MHC expression on TAMs, and improved T-cell responses. Transcriptomic and functional analyses demonstrated that CD300e-deficient macrophages exhibit increased phagocytosis, upregulated antigen presentation, and greater support for T-cell proliferation and cytotoxicity. Adoptive transfer confirmed that macrophage-intrinsic CD300e expression is sufficient to suppress T-cell function and promote tumor growth. Our findings identify CD300e as a critical regulator of macrophage-mediated immune suppression in CRC and a potential target for reprogramming TAMs to enhance immunotherapy.

cancer biology↗

bioRxiv2020

Single cell transcriptome analysis defines novel heterogeneity within the pancreatic ductal tree

Lineage tracing using genetically engineered mouse models is an essential tool for investigating cell-fate decisions of progenitor cells and biology of mature cell types, with relevance to physiology and disease progression. To study disease development, an inventory of an organs cell types and understanding of physiologic function is paramount. Here, we performed single-cell RNA sequencing to examine heterogeneity of murine pancreatic duct cells, pancreatobiliary cells, and intrapancreatic bile duct cells. We describe an epithelial-mesenchymal transitory axis in our three pancreatic duct subpopulations and identify SPP1 as a regulator of this fate decision as well as human duct cell de-differentiation. Our results further identify functional heterogeneity within pancreatic duct subpopulations by elucidating a role for Geminin in accumulation of DNA damage in the setting of chronic pancreatitis. Our findings implicate diverse functional roles for subpopulations of pancreatic duct cells in maintenance of duct cell identity and disease progression and establish a comprehensive road map of murine pancreatic duct cell, pancreatobiliary cell, and intrapancreatic bile duct cell homeostasis. SIGNIFICANCEMurine models are extensively used for pancreatic lineage tracing experiments and investigation of pancreatic disease progression. Here, we describe the transcriptome of murine pancreatic duct cells, intrapancreatic bile duct cells, and pancreatobiliary cells at single cell resolution. Our analysis defines novel heterogeneity within the pancreatic ductal tree and supports the paradigm that more than one population of pancreatic duct cells harbors progenitor capacity. We identify and validate unique functional properties of subpopulations of pancreatic duct cells including an epithelial-mesenchymal transcriptomic axis and roles in chronic pancreatic inflammation.

bioinformatics↗