Biology subjects

Hopp, S. C.

Publications and source records attributed to Hopp, S. C..

4 recordsLinked to original sources

bioRxiv2026

PLCγ2 deficiency compromises systemic immune tolerance and erodes myelin homeostasis while enhancing oxidative metabolism in the mouse brain

BackgroundPhospholipase C gamma-2 (PLC{gamma}2) catalyzes the hydrolysis of the membrane phosphatidylinositol-4,5-bisphosphate (PIP2) to form diacylglycerol (DAG) and inositol trisphosphate (IP3), feeding into diverse downstream signaling pathways. PLCG2 polymorphisms have been associated with reduced and/or increased risk of Alzheimers disease (AD) and related dementias, longevity, autoinflammation, and immune disorders. In the brain, PLC{gamma}2 is expressed in microglia, and other neuroimmune and vascular interface populations, yet its role in brain homeostasis remains incompletely defined. MethodsWe analyzed the brains of three-month-old Plcg2 wild-type (WT), heterozygous (Het KO) and homozygous knockout (Homo KO) littermate mice modeling human PLCG2 loss-of-function risk alleles linked to AD risk using a multiomic approach that included lipidomics, metabolomics, proteomics, and transcriptomics, together with immunofluorescence, as well as flow-cytometric profiling of peripheral and brain-draining immune compartments. ResultsPlcg2 deficiency substantially impaired early survival and produced splenomegaly without increasing total spleen cellularity, instead shifting spleen composition toward myeloid/innate-enriched cells and away from B cells, with expansion of age-associated B-cell (ABC-like) subsets and parallel reductions in CD4 and CD8 regulatory T cells in spleen and cervical lymph nodes. Brain lipidomics revealed selective depletion of PIP2, despite very low bulk PLC{gamma}2 protein abundance relative to other PLC family members. PLC{gamma}2 loss led to significant reductions in myelin-enriched lipid classes and myelin/paranode-associated proteins, accompanied by compensatory upregulation of oligodendrocyte/myelin genes, and modest shifts in microglial, lysosomal, complement, and oxidative metabolism pathways by NanoString and DIA-MS. Targeted acylcarnitine profiling demonstrated reprogramming of brain oxidative metabolism, with increased short-, medium-, and long-chain acylcarnitines and enrichment of mitochondrial matrix fatty-acid and amino-acid catabolic enzymes in Homo KO brains. ConclusionsLoss of PLC{gamma}2 installs a coordinated program that compromises systemic immune tolerance and subtly erodes central myelin and phosphoinositide homeostasis while enhancing brain oxidative metabolism, effects that extend beyond microglial phagocytic signaling and may underlie increased vulnerability to AD pathology and aging, providing a mechanistic framework for how PLCG2 variation may link systemic immune regulation, white-matter integrity, and neurodegenerative risk. LimitationsBecause constitutive Plcg2 Homo KO mice display high early mortality and intestinal vascular abnormalities, observed phenotypes may reflect developmental compensation and may not fully recapitulate protective human PLCG2 variants.

neuroscience↗

bioRxiv2024

Quinolinic acid links kidney injury to brain toxicity

Kidney dysfunction often leads to neurological impairment, yet the complex kidney-brain relationship remains elusive. We employed spatial and bulk metabolomics to investigate a mouse model of rapid kidney failure induced by mouse double minute 2 (Mdm2) conditional deletion in the kidney tubules to interrogate kidney and brain metabolism. Pathway enrichment analysis of focused plasma metabolomics panel pinpointed tryptophan metabolism as the most altered pathway with kidney failure. Spatial metabolomics showed toxic tryptophan metabolites in the kidneys and brains, revealing a novel connection between advanced kidney disease and accelerated kynurenine degradation. In particular, the excitotoxic metabolite quinolinic acid was localized in ependymal cells adjacent to the ventricle in the setting of kidney failure. These findings were associated with brain inflammation and cell death. A separate mouse model of acute kidney injury also had an increase in circulating toxic tryptophan metabolites along with altered brain inflammation. Patients with advanced CKD similarly demonstrated elevated plasma kynurenine metabolites and quinolinic acid was uniquely correlated with fatigue and reduced quality of life in humans. Overall, our study identifies the kynurenine pathway as a bridge between kidney decline, systemic inflammation, and brain toxicity, offering potential avenues for diagnosis and treatment of neurological issues in kidney disease.

molecular biology↗

bioRxiv2023

Multi-omics analyses reveal novel effects of PLCγ2 deficiency in the mouse brain

Phospholipase C gamma-2 (PLC{gamma}2) catalyzes the hydrolysis of the membrane phosphatidylinositol-4,5-bisphosphate (PIP2) to form diacylglycerol (DAG) and inositol trisphosphate (IP3), which subsequently feed into numerous downstream signaling pathways. PLCG2 polymorphisms are associated with both reduced and increased risk of Alzheimers disease (AD) and with longevity. In the brain, PLCG2 is highly expressed in microglia, where it is proposed to regulate phagocytosis, secretion of cytokines/chemokines, cell survival and proliferation. We analyzed the brains of three-month-old PLC{gamma}2 knockout (KO), heterozygous (HET), and wild-type (WT) mice using multiomics approaches, including shotgun lipidomics, proteomics, and gene expression profiling, and immunofluorescence. Lipidomic analyses revealed sex-specific losses of total cerebrum PIP2 and decreasing trends of DAG content in KOs. In addition, PLC{gamma}2 depletion led to significant losses of myelin-specific lipids and decreasing trends of myelin-enriched lipids. Consistent with our lipidomics results, RNA profiling revealed sex-specific changes in the expression levels of several myelin-related genes. Further, consistent with the available literature, gene expression profiling revealed subtle changes on microglia phenotype in mature adult KOs under baseline conditions, suggestive of reduced microglia reactivity. Immunohistochemistry confirmed subtle differences in density of microglia and oligodendrocytes in KOs. Exploratory proteomic pathway analyses revealed changes in KO and HET females compared to WTs, with over-abundant proteins pointing to mTOR signaling, and under-abundant proteins to oligodendrocytes. Overall, our data indicate that loss of PLC{gamma}2 has subtle effects on brain homeostasis that may underlie enhanced vulnerability to AD pathology and aging via novel mechanisms in addition to regulation of microglia function. Significance StatementThe PLCG2 gene contains a number of rare variants linked with increased and decreased risk for Alzheimers disease and longevity, but little is known about the role of PLC{gamma}2 in normal brain function. The results described herein are significant because they describe the effects of knockout of PLC{gamma}2 on brain cell types, thus mimicking the loss of function Alzheimers disease risk mutation. Our data describe novel effects of PLC{gamma}2 deficiency on myelin homeostasis and mTOR signaling that have not been previously described that may underlie its association with Alzheimers disease pathogenesis and longevity.

neuroscience↗

bioRxiv2019

An integrated genomic approach to dissect the genetic landscape regulating the cell-to-cell transfer of a-synuclein

Neuropathological and experimental evidence suggests that the cell-to-cell transfer of a-synuclein has an important role in the pathogenesis of Parkinsons disease (PD). However, the mechanism underlying this phenomenon is not fully understood. We undertook an siRNA, genome-wide high throughput screen to identify genes regulating the cell-to-cell transfer of a-synuclein. We transiently transfected HEK cells stably overexpressing a-synuclein with a construct encoding GFP-2a-aSynuclein-RFP. The cells expressing a-synuclein-RFP through transfection were double positive for GFP and RFP fluorescence, whereas the cells receiving it through transfer were positive only for RFP fluorescence. The amount of a-synuclein transfer was quantified by high content microscopy. A series of unbiased screens confirmed the involvement of 38 genes in the regulation of a-synuclein-RFP transfer. One of those hits was ITGA8, a candidate gene recently identified through a large PD genome wide association study (GWAS). Weighted gene co-expression network analysis (WGCNA) and weighted protein-protein network interaction analysis (WPPNIA) showed that the hits clustered in networks that included known PD Mendelian and GWAS risk genes more frequently than expected than random chance. Given the genetic overlap between a-synuclein transfer and PD, those findings provide supporting evidence for the importance of the cell-to-cell transfer of a-synuclein in the pathogenesis of PD, and expand our understanding of the mechanism of a-synuclein spread.

neuroscience↗