Biology subjects

Quadri, Z.

Publications and source records attributed to Quadri, Z..

4 recordsLinked to original sources

bioRxiv2025

Citrullination of TDP-43 is a key post-translation modification associated with structural and functional changes and progressive pathology in TDP-43 mouse models and human proteinopathies

TAR DNA-binding protein 43 (TDP-43) pathology is associated with a spectrum of clinical dementias including limbic-predominant age-related TDP-43 encephalopathy neuropathological changes (LATE-NC). Post-translational modifications (PTM) are linked to TDP-43 toxic gain-of-function and cytoplasmic aggregation1-3. Phosphorylation remains the most investigated PTM and a standard criterion for determining pathology progression and clinical subclassification in TDP-43 proteinopathies4-7. However, full spectrum of PTMs on TDP-43 structure and biology remain unknown. Utilizing mass-spectrometry analysis we identified citrullination as a novel and irreversible "bona-fide" PTM of TDP-43 protein. We recognized peptidyl arginine deiminase 2 and 4 (PAD2 and PAD4) to mediate the conversion of arginine (R) to citrulline (citR) in vitro and demonstrated increased PAD2 and PAD4 expression and TDP-43 citrullination in a human wildtype TDP-43 mouse model (Tg (Thy1-TARDBP4). Transmission electron microscopy imaging analysis revealed citrullination induced vast structural changes while ThT analysis demonstrated altered aggregation kinetics of citrullinated (citR) TDP-43 protein. We further provided mechanistic evidence on reduced electrostatic and pi-pi interactions of citR TDP-43 Low Complexity Domain (LCD) with RNA, favoring liquid-solid phase separation and condensate formation. Generation and validation of several citR TDP-43 specific antibodies against several TDP-43 epitopes revealed epitope and domain-specific effects of citrullination on TDP-43 solubility in vivo. Importantly, we found distinct reactivities of citR TDP-43 antibodies shedding light into the contribution of epitope-specific properties of human citR TDP-43 to novel pathological citR TDP-43 assemblies in human brain tissue from LATE-NC, with or without comorbid Alzheimers disease neuropathologic changes (ADNC). These findings provided a unique look into the temporal citR TDP-43 signatures, and the potential clinical relevance associated with progression of pure LATE-NC and comorbid ADNC + LATE-NC. Collectively, these data reveal the existence of irreversible TDP-43 citrullination at targeted sites via induced PAD2/PAD4 activities, presenting a critical step in TDP-43 proteinopathy.

neuroscience↗

bioRxiv2024

Probing tau citrullination in Alzheimer's disease brains and mouse models of tauopathy

Tauopathies, which include Alzheimers disease (AD) share a common defining factor, namely misfolded tau protein. However, the "upstream" etiology and downstream clinical manifestations of tauopathies are quite diverse. Tau deposition elicits different pathological phenotypes and outcomes depending on the tau strain and regional susceptibility. Posttranslational modifications (PTM) can alter tau structure, function, networks, and its pathological sequalae. We uncovered a novel PTM of tau, named citrullination, caused by peptidyl arginine deiminase (PAD) enzymes. PAD induced citrullination irreversibly converts arginine residues to citrulline, producing net loss of positive charge, elimination of pi-pi interactions, and increased hydrophobicity. We observed increased PAD2 and PAD4 in Alzheimers disease (AD) brain and that they both can citrullinate tau. Tau can become citrullinated by PADs at all 14 arginine residues throughout the N-terminal domain (N-term), proline-rich domain (PR), microtubule binding repeat domain (MBR), and C-terminal domain (C-term) on full length tau (2N4R). Citrullination of tau impacts fibrillization and oligomerization rates in aggregation assays. Utilizing a panel of novel citrullinated tau (citR tau) antibodies, we identified citrullination of tau in vitro, several animal models of tauopathies, and Alzheimers disease (AD). CitR tau increased with Braak stage and was enriched in AD brains with higher phospho-tau burden. This work provides a new area of tau biology that signifies further consideration in the emerging spectrum of tauopathies and its clinical understanding.

neuroscience↗

bioRxiv2024

Nutrient Sensing Receptor GPRC6A Regulates mTORC1 Signaling and Tau Biology

Tauopathies, including Alzheimers disease (AD), comprise microtubule-associated protein tau aggregates that cause neuronal cell death and clinical cognitive decline. Reducing overall tau abundance remains a central strategy for therapeutics; however, no disease-modifying treatment exists to date. One principal pathway for balancing cellular proteostasis includes the mechanistic target of rapamycin complex 1 (mTORC1) signaling. Recently, arginine emerged as one of the primary amino acids to activate mTORC1 through several intracellular arginine sensors and an extracellular arginine receptor, namely the G protein-coupled receptor (GPCR) family C, group 6, member A (GPRC6A). Human AD brains were previously reported with elevated mTORC1 signaling; however, it is unclear whether arginine sensing and signaling to mTORC1 plays a role in tauopathies. Herein, we examined arginine sensing associated with mTORC1 signaling in the human AD and animal models of tauopathy. We found that human AD brains maintained elevated levels of arginine sensors with potential uncoupling of arginine sensing pathways. Furthermore, we observed increased GPRC6A and arginine in the brain, accompanied by increased mTORC1 signaling and decreased autophagy in a mouse model of tauopathy (Tau PS19). We also discovered that both supplementing arginine and overexpressing GPRC6A in cell culture models could independently activate mTORC1 and promote tau accumulation. In addition, we found that suppressing GPRC6A signaling by either genetic reduction or pharmacological antagonism reduced tau accumulation, phosphorylation, and oligomerization. Overall, these findings uncover the crucial role of arginine sensing pathways in deregulating mTORC1 signaling in tauopathies and identify GPRC6A as a promising target for future therapeutics in tauopathies and other proteinopathies. Significance StatementTauopathies, including Alzheimers disease (AD), accumulate pathogenic tau protein inclusions that potentially contribute to the hyperactive mechanistic target of rapamycin complex 1 (mTORC1) signaling and eventually cause neuronal cell death. Here, we presented novel findings that AD and animal models of tauopathy maintained increased expression of arginine sensors and uncoupling of arginine sensing associated with mTORC1 signaling. We investigated the role of a putative extracellular arginine and basic L-amino acid sensing G protein-coupled receptor (GPCR) family C, group 6, member A (GPRC6A) in activating mTORC1 and accelerating pathogenic tau phenotypes in several cell models. Additionally, we showed that genetic repression or antagonism of GPRC6A signaling provides a novel therapeutic target for tauopathies and other proteinopathies.

neuroscience↗

bioRxiv2021

Regulation of brain aging by neutral sphingomyelinase 2

We have shown that deficiency of neutral sphingomyelinase 2 (nSMase2), an enzyme generating the sphingolipid ceramide, improves memory in adult mice. Here, we performed sphingolipid and RNA-seq analyses on the cortex from 10 month-old nSMase2-deficient (fro/fro) and heterozygous (+/fro) mice. fro/fro cortex showed reduced levels of ceramide, particularly in astrocytes. Differentially abundant transcripts included several functionally related groups, with decreases in mitochondrial oxidative phosphorylation and astrocyte activation transcripts, while axon guidance and synaptic transmission transcripts were increased, indicating a role of nSMase2 in oxidative stress, astrocyte activation, and cognition. Experimentally induced oxidative stress decreased the level of glutathione (GSH), an endogenous inhibitor of nSMase2, and increased immunolabeling for ceramide in primary +/fro astrocytes, but not in fro/fro astrocytes. {beta}-galactosidase activity was lower in 5-weeks old fro/fro astrocytes, indicating delayed senescence due to nSMase2 deficiency. In fro/fro cortex, levels of the senescence markers C3b and p27, and the proinflammatory cytokines interleukin 1{beta}, interleukin 6, and tumor necrosis factor were reduced, concurrent with 2-fold decreased phosphorylation of their downstream target, protein kinase Stat3. RNA and protein levels of the ionotropic glutamate receptor subunit 2b (Grin2b or NR2B) were increased by 2-fold, an effect known to enhance cognition. This was consistent with 3.5-fold reduced levels of exosomes carrying miR-223-3p, a micro-RNA downregulating Grin2b. In summary, our data show that nSMase2 deficiency prevents oxidative stress-induced elevation of ceramide and secretion of exosomes by astrocytes that suppress neuronal function, indicating a role of nSMase2 in the regulation of neuroinflammation and cognition during brain aging. Significance statementOxidative stress is associated with brain aging and cognitive decline. The underlying mechanism how oxidative stress impairs brain function is still not clear. We provide evidence that oxidative stress increases ceramide in astrocytes, which is prevented by deficiency of nSMase2, an enzyme that is activated by oxidative stress and generates ceramide from sphingomyelin. Mass spectrometric and transciptomic (RNA-seq) analyses show that in middle aged (10-month old) mouse cortex, nSMase2 deficiency reduces ceramide and increases expression of genes important for synaptic transmission and cognition. Therefore, our data show that oxidative stress-induced activation of nSMase2 and generation of ceramide is significant for cognitive decline during aging.

neuroscience↗