Biology subjects

Koliwad, S. K.

Publications and source records attributed to Koliwad, S. K..

6 recordsLinked to original sources

bioRxiv2026

ApoE-Dependent Lipid Handling by Median Eminence Microglia Preserves Myelin Integrity and Metabolic Function

Microglia regulate hypothalamic control of systemic metabolism, but the mechanisms underlying their contribution remain unclear. Here, we identify a distinct apolipoprotein E (ApoE) microglial population enriched in the median eminence (ME), a brain region involved in sensing peripheral cues and metabolic regulation. These microglia engage multiple functional programs related to lipid handling, interferon signaling, and stress responses that are differentially regulated within the ME. Consumption of a Western diet (WD) increased interferon signaling and lipid accumulation in ME microglia. Expression of the human APOE4 isoform in mice exacerbated microglial lipid dysregulation, interferon signaling, and impaired ME myelin organization. Deleting APOE in microglia attenuated their ability to couple lipid accumulation to interferon signaling, identifying microglial APOE as a cell-intrinsic determinant of interferon responses. Finally, selective activation of liver X receptor signaling using synthetic HDL nanoparticles restored microglial lipid homeostasis, improved hypothalamic leptin responsiveness, and limited weight gain in WD-fed mice. Together, these findings define an Apoe-dependent regulatory program in ME microglia that is therapeutically targetable and clarify how nutritional stress disrupts hypothalamic control of metabolic homeostasis.

neuroscience↗

bioRxiv2026

Osteoprotegerin-Enabled Immune Evasion by Pathological Adipose Stromal Cells Drives Metabolic Dysfunction in Obesity

Diet-induced obesity (DIO) promotes the accumulation of stromal cells with senescent characteristics in the adipose tissue (AT). Selectively clearing these cells--either through chemical senolytics or activation of invariant natural killer T (iNKT) cells--improves glucose homeostasis in obese mice, however the identity of the responsible stromal population remains unknown. Here, we use transcriptional profiling of AT stromal cells coupled with C12FDG-based enrichment of senescent populations in mice with DIO and healthy controls to identify a distinct subset of adipose progenitor cells (APCs) with robust senescence signatures that accumulate in DIO across multiple AT depots. We show that these cells, which we term senescent APCs (sAPCs), are not merely passive markers of metabolic stress but are instead active stromal organizers, accumulating in parallel with the emergence of lipid-associated macrophages (LAMs) and the diminution of multipotent mesenchymal progenitors. sAPCs promoted CCR2-dependent macrophage chemotaxis, directly linking stromal senescence to chemokine-mediated remodeling of the AT immune niche. Comparative transcriptional analysis revealed a remarkable similarity between sAPCs and inflammatory cancer-associated fibroblasts (iCAFs), including the strong induction of periostin (POSTN) and the production of osteoprotegerin (OPG), a decoy receptor for RANKL and TRAIL that enables tumoral immune evasion. Indeed, OPG production by AT stromal cells was induced by DIO across AT depots. Exogenous OPG inhibited the ability of iNKT cells to kill senescent APCs in vitro, whereas antibody-mediated OPG neutralization reciprocally enhanced such cytotoxic killing. In vivo, systemic OPG neutralization both reduced sAPC accumulation in AT and normalized glucose homeostasis in obese mice. Together, these findings identify sAPCs as a pathological stromal population that expands in obesity through elaboration of immunomodulatory factors. In particular, secreted OPG enables sAPCs to evade iNKT-mediated immune surveillance and contributes to metabolic dysfunction, highlighting OPG and sAPCs as promising therapeutic targets for restoring AT immune and metabolic homeostasis.

immunology↗

bioRxiv2024

Microglia mediate the early-life programming of adult glucose control

Mammalian glucose homeostasis is, in part, nutritionally programmed during early neonatal life, a critical window for the formation of synapses between hypothalamic glucoregulatory centers. Although microglia are known to prune synapses throughout the brain, their specific role in refining hypothalamic glucoregulatory circuits remains unknown. Here, we show that microglia in the mediobasal hypothalamus (MBH) of mice actively engage in synaptic pruning during early life. Microglial phagocytic activity is induced following birth, regresses upon weaning from maternal milk, and is exacerbated by feeding dams a high-fat diet while lactating. In particular, we show that microglia refine perineuronal nets (PNNs) within the neonatal MBH. Indeed, transiently depleting microglia before weaning (P6-16), but not afterward (P21-31), remarkably increased PNN abundance in the MBH. Furthermore, mice lacking microglia only from P6-16 had glucose intolerance due to impaired glucose-responsive pancreatic insulin secretion in adulthood, a phenotype not seen if microglial depletion occurred after weaning. Viral retrograde tracing revealed that this impairment is linked to a reduction in the number of neurons in specific hypothalamic glucoregulatory centers that synaptically connect to the pancreatic {beta}-cell compartment. These findings show that microglia facilitate synaptic plasticity in the MBH during early life through a process that includes PNN refinement, to establish hypothalamic circuits that regulate adult glucose homeostasis.

physiology↗

bioRxiv2022

Microglial inflammatory activation paradoxically improves glucose tolerance during diet-induced obesity

Hypothalamic gliosis associated with high fat diet (HFD) feeding increases susceptibility to hyperphagia and weight gain, and is therefore presumed to promote obesity-associated consequences such as glucose intolerance as well. Nevertheless, the body weight-independent contribution of microglial activation to glucose regulation has not been determined. Here we show that reducing microglial NF-{kappa}B signaling via cell-specific IKK{beta} deletion exacerbates HFD-induced glucose intolerance and insulin resistance despite reducing body weight and adiposity. This effect was associated with reduced activity of hypothalamic glucose sensing neurons. Conversely, a genetic approach to increase microglial inflammatory activity improved glucose tolerance independently of diet in lean rodents. To avoid confounding effects due to chronic alterations to microglial signaling pathways from dietary or genetic interventions, we developed an inducible model of microglial activation using DREADD-based chemogenetics. Gq-coupled GPCR activation rapidly increased microglial calcium levels, cytokine gene expression, and morphological hallmarks of inflammatory activation. In both lean and obese rodents, chemogenetic microglial activation caused a marked improvement in glucose tolerance along with increased activation of hypothalamic glucose sensing neurons, effects abrogated by central blockade of TNF signaling. Thus, while diet-induced microglial activation promotes weight gain, it may also serve an adaptive function--to prevent the deterioration of glucose tolerance associated with obesity, an important consideration for immune-modulating metabolic therapies.

neuroscience↗

bioRxiv2020

Differences in the gut microbiomes of distinct ethnicities within the same geographic area are linked to host metabolic health

BackgroundThe human gut microbiota exhibits marked variation around the world, which has been attributed to dietary intake and other environmental factors. However, the degree to which ethnicity-associated differences in gut microbial community structure and function are maintained following immigration or in the context of metabolic disease is poorly understood. ResultsWe conducted a multi-omic study of 46 lean and obese East Asian and White participants living in the San Francisco Bay Area. 16S rRNA gene sequencing revealed significant differences between ethnic groups in bacterial richness and community structure. White individuals were enriched for the mucin-degrading Akkermansia muciniphila. East Asian participants had increased levels of multiple bacterial phyla, fermentative pathways detected by metagenomics, and the short-chain fatty acid end products acetate, propionate, and isobutyrate. Differences in the gut microbiota between the East Asian and White groups could not be explained by reported dietary intake, were more pronounced in lean individuals, and were associated with current geographical location. Microbiome transplantations into germ-free mice confirmed that the differences in the gut microbiota of the East Asian and White individuals we analyzed are independent of diet and that they differentially impact host body weight and adiposity in genetically identical mouse recipients. ConclusionsThe reported findings emphasize the utility of studying diverse ethnic groups within a defined geographical location and provide a starting point for dissecting the mechanisms contributing to the complex interactions between the gut microbiome and ethnicity-associated lifestyle, demographic, metabolic, and genetic factors.

microbiology↗

bioRxiv2018

The Genetic Basis for the Cooperative Bioactivation of Plant Lignans by a Human Gut Bacterial Consortium

Plant-derived lignans, consumed daily by most individuals, are inversely associated with breast cancer; however, their bioactivity is only exerted following gut bacterial conversion to enterolignans. Here, we dissect a four-species bacterial consortium sufficient for all four chemical reactions in this pathway. Comparative genomics and heterologous expression experiments identified the first enzyme in the pathway. Transcriptional profiling (RNAseq) independently identified the same gene and linked a single genomic locus to each of the remaining biotransformations. Remarkably, we detected the complete bacterial lignan metabolism pathway in the majority of human gut microbiomes. Together, these results are an important step towards a molecular genetic understanding of the gut bacterial bioactivation of lignans and other plant secondary metabolites to downstream metabolites relevant to human disease.\n\nOne Sentence SummaryBess et al. provide a first step towards elucidating the molecular genetic basis for the cooperative gut bacterial bioactivation of plant lignans, consumed daily by most individuals, to phytoestrogenic enterolignans.

microbiology↗