Biology subjects

Aggarwal, G.

Publications and source records attributed to Aggarwal, G..

9 recordsLinked to original sources

bioRxiv2026

Progranulin deficiency promotes neuroinflammation through cathepsin B-mediated activation of the NLRP3 inflammasome

Haploinsufficiency of progranulin (resulting from mutations in the GRN gene) is a major genetic cause of frontotemporal dementia (FTD), which is characterized by profound changes in personality and behavior, progressive impairments in executive function, speech, language and/or movement, TDP-43 pathology, lysosomal dysfunction, and neuroinflammation. Studies in progranulin-deficient mouse models have demonstrated the critical role of neuroinflammation in disease pathogenesis, as deletion of NF-kB or complement factors prevents FTD-associated behavioral deficits. While progranulin is known to be anti-inflammatory, the precise molecular mechanism by which its deficiency triggers inflammatory cascades remain unclear. Here, we investigate the involvement of the NLRP3 inflammasome in progranulin-deficient models, including mice, human microglial cells, and patient fibroblasts. In Grn mice, we found increased levels of several inflammasome-related proteins, including procaspase-1 and cleaved IL-1{beta}. Similarly, GRN knockout (KO) microglia cells showed significant increases in levels of procaspase-1, NLRP3, and cleaved IL-1{beta}. Moreover, KO cells had increased NLRP3 oligomerization, suggesting that progranulin negatively regulates inflammasome assembly. We also investigated the potential link between lysosomal dysfunction and NLRP3 inflammasome activation in progranulin deficiency. We found that pharmacological inhibition of cathepsin B reduced NLRP3 inflammasome oligomerization as well as inflammatory cytokine expression in GRN KO cells. Additionally, siRNA knockdown of cathepsin B reduced levels of procaspase-1 and cleaved IL-1{beta} in GRN KO cells. Finally, we found that heterozygous GRN fibroblasts exhibited similar increases in procaspase-1 and cleaved IL-1{beta} levels, and these increases were corrected by treatment with an antisense oligonucleotide (ASO) that increase progranulin protein levels. Overall, our results demonstrate that progranulin deficiency promotes NLRP3 inflammasome assembly and activity through cathepsin B-mediated signaling, thereby establishing a mechanistic link between lysosomal dysfunction and increased inflammation. The ability of the GRN-targeting ASO to correct NLRP3-mediated inflammation highlights a promising therapeutic strategy for FTD-GRN and inflammation in other neurodegenerative disorders linked to progranulin deficiency.

neuroscience↗

bioRxiv2025

Mutations in Hsp40 co-chaperone change the unique canonical inter-domain interactions stimulating LGMDD1 myopathy

Limb-girdle muscular dystrophy D1 (LGMDD1) is a rare, dominantly inherited neuromuscular disorder caused by mutations in the HSP40 co-chaperone DNAJB6, primarily in the GF or J-domains. Currently, no treatments are available, and a challenge in understanding the disease is identifying a specific client protein for DNAJB6 in skeletal muscle. Our previous research indicated that LGMDD1 GF domain mutants in Sis1 exhibit substrate-specific effects, influenced by HSP70 activity. Herein, we found that novel mutations in the J-domain similarly affected chaperone function. The J-domain mutants exhibited variable substrate processing, reduced binding affinity to client-substrate, and decreased stimulation of Ssa1 ATP hydrolysis, with these effects being substrate-conformer-specific. Our simulation studies noted differences in inter-domain interactions linked to the mutants, which influence the Hsp40-Hsp70 ATPase cycle. These mechanistic insights enhance our understanding of LGMDD1 myopathy and help to identify potential treatment strategies in the future. TeaserRecalibrating the inter-domain interface of the mutant protein could potentially serve as a key therapeutic strategy for LGMDD1 myopathy.

biochemistry↗

bioRxiv2023

Biochemical, biomarker, and behavioral characterization of the GrnR493X mouse model of frontotemporal dementia

Heterozygous loss-of-function mutations in the progranulin gene (GRN) are a major cause of frontotemporal dementia due to progranulin haploinsufficiency; complete deficiency of progranulin causes neuronal ceroid lipofuscinosis. Several progranulin-deficient mouse models have been generated, including both knockout mice and knockin mice harboring a common patient mutation (R493X). However, the GrnR493X mouse model has not been characterized completely. Additionally, while homozygous GrnR493X and Grn knockout mice have been extensively studied, data from heterozygous mice is still limited. Here, we performed more in-depth characterization of heterozygous and homozygous GrnR493X knockin mice, which includes biochemical assessments, behavioral studies, and analysis of fluid biomarkers. In the brains of homozygous GrnR493X mice, we found increased phosphorylated TDP-43 along with increased expression of lysosomal genes, markers of microgliosis and astrogliosis, pro-inflammatory cytokines, and complement factors. Heterozygous GrnR493X mice did not have increased TDP-43 phosphorylation but did exhibit limited increases in lysosomal and inflammatory gene expression. Behavioral studies found social and emotional deficits in GrnR493X mice that mirror those observed in Grn knockout mouse models, as well as impairment in memory and executive function. Overall, the GrnR493X knockin mouse model closely phenocopies Grn knockout models. Lastly, in contrast to homozygous knockin mice, heterozygous GrnR493X mice do not have elevated levels of fluid biomarkers previously identified in humans, including neurofilament light chain (NfL) and glial fibrillary acidic protein (GFAP) in both plasma and CSF. These results may help to inform pre-clinical studies that use this Grn knockin mouse model and other Grn knockout models.

neuroscience↗

bioRxiv2022

Inferring light responses of primate retinal ganglion cells using intrinsic electrical signatures

Reproducing high-acuity vision with an epiretinal implant will likely require inferring the natural light responses of diverse RGC types in the implanted retina, without measuring them directly. Here we demonstrate an approach that exploits intrinsic electrical features of primate RGCs. First, ON-parasol and OFF-parasol RGCs were identified with 95% accuracy using electrical features. Then, the somatic electrical footprint, predicted cell type, and average linear-nonlinear-Poisson model parameters of each cell type were used to infer a light response model for each cell. Across five retinas, these models achieved an average correlation with measured firing rates of 0.49 for white noise visual stimuli and 0.50 for natural scenes stimuli, compared to 0.65 and 0.58 respectively for models fitted to recorded light responses, an upper bound. This finding, and linear decoding of images from predicted RGC activity, suggested that the inference approach may be useful for high-fidelity sight restoration.

neuroscience↗

bioRxiv2022

Antisense oligonucleotide-based therapeutic strategy for progranulin-deficient frontotemporal dementia

Heterozygous GRN (progranulin) mutations cause frontotemporal dementia (FTD) due to haploinsufficiency, and increasing progranulin levels is a major therapeutic goal. Several microRNAs, including miR-29b, negatively regulate progranulin protein levels. Antisense oligonucleotides (ASOs) are emerging as a promising therapeutic modality for neurological diseases, but strategies for increasing target protein levels are limited. Here, we tested the efficacy of ASOs as enhancers of progranulin expression by sterically blocking the miR-29b binding site in the 3 UTR of the human GRN mRNA. We found 16 ASOs that increase progranulin protein in a dose-dependent manner in neuroglioma cells. A subset of these ASOs also increased progranulin protein in iPSC-derived neurons and in a humanized GRN mouse model. In FRET-based assays, the ASOs effectively competed miR-29b from binding to the GRN 3 UTR RNA. The ASOs increased levels of newly synthesized progranulin protein by increasing its translation, as revealed by ribosomal profiling. Together, our results demonstrate that ASOs can be used to effectively increase target protein levels by partially blocking miR binding sites. This ASO strategy may be therapeutically feasible for progranulin-deficient FTD as well as other conditions of haploinsufficiency.

neuroscience↗

bioRxiv2021

Progranulin deficiency results in reduced bis(monoacylglycero)phosphate (BMP) levels and gangliosidosis

Homozygous mutations of granulin precursor (GRN) lead to neuronal ceroid lipofuscinosis1, a severe neurodevelopmental disease, in humans and neuroinflammation in mice2. Haploinsufficiency of GRN almost invariably causes frontotemporal dementia (FTD)3,4. The GRN locus produces progranulin (PGRN), a lysosomal precursor protein that is cleaved to granulin peptides5,6. Despite intensive investigation, the function of granulins and the reason why their absence causes neurodegeneration remain unclear. Here, we investigated PGRN function in lipid degradation, a major function of lysosomes. We show that PGRN-knockout human cells, PGRN-deficient murine brain, and frontal lobes of human brains from patients with GRN mutation-related FTD have increased levels of gangliosides, highly abundant sialic acid-containing glycosphingolipids (GSL) that are degraded in lysosomes. Probing how PGRN deficiency causes these changes, we found normal levels and activities of enzymes that catabolize gangliosides. However, levels of bis(monoacylglycero)phosphate (BMP), a lysosomal lipid required for ganglioside catabolism7, were markedly reduced in PGRN-deficient cells and patient brain tissues. These data indicate that granulins are required to maintain BMP levels, which regulate ganglioside catabolism, and that PGRN deficiency in lysosomes leads to gangliosidosis. This aberrant accumulation of gangliosides may contribute to neuroinflammation and neurodegeneration susceptibility.

cell biology↗

bioRxiv2020

Focal Electrical Stimulation of Human Retinal Ganglion Cells

Vision restoration with retinal implants that electrically stimulate retinal ganglion cells (RGCs), which transmit visual information to the brain, is limited by indiscriminate activation of many cells and cell types. Recent work in isolated macaque retina has demonstrated that direct electrical stimulation of RGCs can be performed with single-cell, single-spike resolution. However, the fidelity of epiretinal stimulation has not been examined in the human retina. Here, electrical activation of the major RGC types was examined using large-scale, multi-electrode recording and stimulation in the human retina ex vivo and compared directly to results from macaque. Targeted activation with single-cell, single-spike resolution was often possible without activating overlying axon bundles, at low stimulation current levels similar to those in macaque. Distinct cell types could be identified and targeted based on their distinct electrical signatures. Simulation based on these measurements revealed that a novel, dynamic stimulation approach would produce a nearly optimal evoked visual signal. These results indicate that high-fidelity control of spiking in human RGCs is achievable with extracellular stimulation and that the macaque retina is an accurate model for vision restoration with epiretinal implants.

neuroscience↗

bioRxiv2020

Symmetrically substituted dichlorophenes inhibit N-acyl-phosphatidylethanolamine phospholipase D

N-acyl-phosphatidylethanolamine phospholipase D (NAPE-PLD) (EC 3.1.4.4) catalyzes the final step in the biosynthesis of N-acyl-ethanolamides (NAEs). Reduced NAPE-PLD expression and activity may contribute to obesity and inflammation, but a major obstacle to elucidating the role of NAPE-PLD and NAE biosynthesis in various physiological processes has been the lack of effective NAPE-PLD inhibitors. The endogenous bile acid lithocholic acid (LCA) inhibits NAPE-PLD activity (IC50 68 M) but LCA is also a highly potent ligand for TGR5 (EC50 0.52 M). Recently, the first selective small molecule inhibitor of NAPE-PLD, ARN19874, was reported (IC50 34 M). To identify more potent inhibitors of NAPE-PLD, we screened compounds using a quenched fluorescent NAPE analog, PED-A1, as a substrate for recombinant mouse NAPE-PLD. Screened compounds included a panel of bile acids as well as a library of experimental compounds (the Spectrum Collection). Muricholic acids and several other bile acids inhibited NAPE-PLD with potency similar to LCA. Fourteen potent NAPE-PLD inhibitors were identified in the Spectrum Collection, with the two most potent (IC50 ~2 M) being symmetrically substituted dichlorophenes: hexachlorophene and bithionol. Structure activity relationship assays using additional substituted dichlorophenes identified key moieties needed for NAPE-PLD inhibition. Both hexachlorophene and bithionol showed significant selectivity for NAPE-PLD compared to non-target lipase activities such as S. chromofuscus PLD activity or serum lipase activity. Both also effectively inhibited NAPE-PLD activity in cultured HEK293 cells.

biochemistry↗

bioRxiv2017

Prediction of Epileptic Seizures based on Mean Phase Coherence

Around 1-2 % of the world's population suffers from epilepsy and 20 % of that vulnerable mass can't be cured through surgery or medicine. Epileptic seizures often occur unpredictably and may cause serious damage to the patient in adverse situations, for e.g. getting a seizure while driving or crossing a road can be fatal. In such a scenario, a reliable mechanism to predict the onset of seizure beforehand is much desirable. In this study, A reliable real-time technique for prediction of epileptic seizures is presented. Mean Phase Coherence (MPC), as a measure of phase synchronization, is used to predict impending seizures in a multi-channel EEG data. It was found that during the pre-ictal stages, MPC values and thus phase synchronization between various channels was found to drop significantly below the level in a non-ictal EEG signal. The range of the prediction horizon for seizures varied from 4-10 mins and prediction of impending seizure attack is possible for 8 out of 10 test cases.

neuroscience↗