Biology subjects

Kamat, S. S.

Publications and source records attributed to Kamat, S. S..

4 recordsLinked to original sources

bioRxiv2024

PPARγ mediated enhanced lipid biogenesis fuels Mycobacterium tuberculosis growth in hepatocytes.

Mycobacterium tuberculosis (Mtb) infection of the lungs, besides producing prolonged cough with mucus, also causes progressive fatigue and cachexia with debilitating loss of muscle mass. While anti-tuberculosis (TB) drug therapy is directed toward eliminating bacilli, the treatment regimen ignores the systemic pathogenic derailments that probably dictate TB-associated mortality and morbidity. Presently, it is not understood whether Mtb spreads to metabolic organs and brings about these impairments. Here we show that Mtb creates a replication-conducive milieu of lipid droplets in hepatocytes by upregulating transcription factor PPAR{gamma} and scavenging lipids from the host cells. In hepatocytes, Mtb shields itself against the common anti-TB drugs by inducing drug-metabolizing enzymes. Infection of the hepatocytes in the in vivo aerosol mice model can be consistently observed post-week 4 along with enhanced expression of PPAR{gamma} and drug-metabolizing enzymes. Moreover, histopathological analysis indeed shows the presence of Mtb in hepatocytes along with granuloma-like structures in human biopsied liver sections. Hepatotropism of Mtb during the chronic infectious cycle results in immuno-metabolic dysregulation that could magnify local and systemic pathogenicity, altering clinical presentations.

microbiology↗

bioRxiv2023

Identification of Sequence Determinants for the ABHD14 Enzymes

Over the course of evolution, enzymes have developed remarkable functional diversity in catalyzing important chemical reactions across various organisms, and understanding how new enzyme functions might have evolved remains an important question in modern enzymology. To systematically annotate functions, based on protein sequences and available biochemical studies, enzymes with similar catalytic mechanisms and/or aspects of catalysis have been clustered together into an enzyme superfamily. Typically, enzymes within a superfamily have similar overall three-dimensional structures, conserved key catalytic residues, but large variations in substrate recognition sites and residues to accommodate the diverse biochemical reactions that are catalyzed within the superfamily. The serine hydrolases are an excellent example of such an enzyme superfamily, that based on known enzymatic activities and protein sequences, is split almost equally into the serine proteases and metabolic serine hydrolases. Within the metabolic serine hydrolases, are two outlying members, ABHD14A and ABHD14B, that have high sequence similarity, but their functions remained cryptic till recently. While ABHD14A still lacks any functional annotation to date, we recently showed that ABHD14B functions as a lysine deacetylase in mammals. Given their high sequence similarity, automated databases wrongly assign ABHD14A and ABHD14B as the same enzyme, and therefore, annotating functions to them in various organisms maybe problematic. In this paper, we present a bioinformatics study coupled to biochemical experiments, that identifies key sequence determinants for both ABHD14A and ABHD14B, and enables better classification for them. Additionally, we map these enzymes on an evolutionary timescale, and provide a resource in studying these interesting enzymes in different organisms.

biochemistry↗

bioRxiv2022

DIP2 is a unique regulator of diacylglycerol lipid homeostasis in eukaryotes

Chain-length specific subsets of diacylglycerol (DAG) lipids are proposed to regulate differential physiological responses ranging from signal transduction to modulation of the membrane properties. However, the mechanism or molecular players regulating the subsets of DAG species remains unknown. Here, we uncover the role of a conserved eukaryotic protein family, DISCO-interacting protein 2 (DIP2) as a homeostatic regulator of a chemically distinct subset of DAGs using yeast, fly and mouse models. Genetic and chemical screens along with lipidomics analysis in yeast reveal that DIP2 prevents the toxic accumulation of specific DAGs in the logarithmic growth phase, which otherwise leads to endoplasmic reticulum stress. We also show that the fatty acyl-AMP ligase-like domains of DIP2 are essential for the redirection of the flux of DAG subspecies to storage lipid, triacylglycerols. Such modulation of selective DAG abundance by DIP2 is found to be crucial for optimal vacuole-membrane fusion and consequently osmoadaptation in yeast. Thus, the study illuminates an unprecedented DAG metabolism route and provides new insights on how cell fine-tunes DAG subspecies for cellular homeostasis and environmental adaptation.

biochemistry↗

bioRxiv2021

The loss of enzymatic activity of the PHARC associated lipase ABHD12 results in increased phagocytosis that causes neuroinflammation

Phagocytosis is an important evolutionary conserved process, essential for clearing pathogens and cellular debris in higher organisms, including humans. This well-orchestrated innate immunological response is intricately regulated by numerous cellular factors, important amongst which, are the immunomodulatory lysophosphatidylserines (lyso-PSs) and the pro-apoptotic oxidized phosphatidylserines (PSs) signaling lipids. Interestingly, in mammals, both these signaling lipids are physiologically regulated by the lipase ABHD12, mutations of which, cause the human neurological disorder PHARC. Despite the biomedical significance of this lipase, detailed mechanistic studies and the specific contribution of ABHD12 to innate processes like phagocytosis remain poorly understood. Here, by immunohistochemical and immunofluorescence approaches, using the murine model of PHARC, we show, that upon an inflammatory stimulus, activated microglial cells in the cerebellum of mice deficient in ABHD12 have an amoeboid morphology, increased soma size, and display heightened phagocytosis activity. We also report that upon an inflammatory stimulus, cerebellar levels of ABHD12 increase to possibly metabolize the heightened oxidized PS levels, temper phagocytosis and in turn control neuroinflammation during oxidative stress. Next, to complement these findings, using biochemical approaches in cultured microglial cells, we show that the pharmacological inhibition and/or genetic deletion of ABHD12 results in increased phagocytic uptake in a fluorescent bead uptake assay. Together, our studies provide compelling evidence that ABHD12 plays an important role in regulating phagocytosis in cerebellar microglial cells, and provides a possible explanation, as to why human PHARC subjects display neuroinflammation and atrophy in the cerebellum.

neuroscience↗