Biology subjects

Fitzgerald, G.

Publications and source records attributed to Fitzgerald, G..

5 recordsLinked to original sources

bioRxiv2023

GLUD1 dictates muscle stem cell differentiation by controlling mitochondrial glutamate levels

Muscle stem cells (MuSCs) enable muscle growth and regeneration after exercise or injury. Upon activation MuSCs metabolically rewire to meet the changing demands of proliferation. Here we describe that primary changes in metabolism itself can dictate MuSC fate decisions to control differentiation and fusion. We found that glutamine anaplerosis into the TCA cycle decreases during MuSC differentiation and coincides with decreased expression of the mitochondrial glutamate deaminase GLUD1. Genetic deletion of Glud1 in proliferating MuSCs resulted in precocious differentiation and imbalanced fusion combined with loss of self-renewal in vitro and in vivo. Mechanistically, deleting Glud1 caused mitochondrial glutamate accumulation in proliferating MuSCs and inhibited the malate-aspartate shuttle (MAS). Restoring MAS activity by supplementation of alanine normalized differentiation. In conclusion, high GLUD1 activity in proliferating MuSCs prevents deleterious mitochondrial glutamate accumulation and inactivation of the MAS. It thereby acts as a compartment specific metabolic brake on MuSC differentiation. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=194 SRC="FIGDIR/small/560525v1_ufig1.gif" ALT="Figure 1"> View larger version (49K): org.highwire.dtl.DTLVardef@e3585dorg.highwire.dtl.DTLVardef@1be4a54org.highwire.dtl.DTLVardef@1f077org.highwire.dtl.DTLVardef@15220f1_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIGlutamine is the major TCA cycle substrate in MuSCs with decreasing contribution upon differentiation. C_LIO_LILoss of Glud1 impairs MuSC self-renewal capacity and causes imbalanced fusion in vitro and in vivo. C_LIO_LIGlud1 deletion leads to mitochondrial glutamate trapping and malate-aspartate shuttle (MAS) dysfunction. C_LIO_LIRestoration of MAS activity in Glud1 deficient MuSCs reverses precocious differentiation and imbalanced fusion. C_LI

cell biology↗

bioRxiv2023

Deep Phenotyping of the Lipidomic Response in COVID and non-COVID Sepsis

Lipids may influence cellular penetrance by pathogens and the immune response that they evoke. Here we find a broad based lipidomic storm driven predominantly by secretory (s) phospholipase A2 (sPLA2) dependent eicosanoid production occurs in patients with sepsis of viral and bacterial origin and relates to disease severity in COVID-19. Elevations in the cyclooxygenase (COX) products of arachidonic acid (AA), PGD2 and PGI2, and the AA lipoxygenase (LOX) product, 12-HETE, and a reduction in the high abundance lipids, ChoE 18:3, LPC-O-16:0 and PC-O-30:0 exhibit relative specificity for COVID-19 amongst such patients, correlate with the inflammatory response and link to disease severity. Linoleic acid (LA) binds directly to SARS-CoV-2 and both LA and its di-HOME products reflect disease severity in COVID-19. AA and LA metabolites and LPC-O-16:0 linked variably to the immune response. These studies yield prognostic biomarkers and therapeutic targets for patients with sepsis, including COVID-19. An interactive purpose built interactive network analysis tool was developed, allowing the community to interrogate connections across these multiomic data and generate novel hypotheses.

systems biology↗

bioRxiv2022

MME+ fibro-adipogenic progenitors are the dominant adipogenic population during fatty infiltration in human skeletal muscle

Summary/Abstract Fatty infiltration, the ectopic deposition of adipose tissue within skeletal muscle, is mediated via the adipogenic differentiation of fibro-adipogenic progenitors (FAPs). We used single-nuclei and single- cell RNA sequencing to characterize FAP heterogeneity in patients with fatty infiltration. We identified an MME+ FAP subpopulation which, based on ex vivo characterization as well as transplantation experiments, exhibits high adipogenic potential. MME+ FAPs are characterized by low activity of WNT, known to control adipogenic commitment, and are refractory to the inhibitory role of WNT activators. Using preclinical models for muscle damage versus fatty infiltration, we show that many MME+ FAPs undergo apoptosis during muscle regeneration and differentiate into adipocytes under pathological conditions, leading to their depletion. Finally, we utilized the varying fat infiltration levels in human hip muscles to show the depletion of MME+ FAPs in fatty infiltrated human muscle. Altogether, we have identified the dominant adipogenic FAP subpopulation in skeletal muscle.

cell biology↗

bioRxiv2021

Tonic inhibition of the chloride/proton antiporter ClC-7 by PI(3,5)P2 is crucial for lysosomal pH maintenance

The acidic luminal pH of lysosomes, maintained within a narrow range, is essential for proper degrative function of the organelle and is generated by the action of a V-type H+ ATPase, but other pathways for ion movement are required to dissipate the voltage generated by this process. ClC-7, a Cl-/H+ antiporter responsible for lysosomal Cl- permeability, is a candidate to contribute to the acidification process as part of this "counterion pathway". The signaling lipid PI(3,5)P2 modulates lysosomal dynamics, including by regulating lysosomal ion channels, raising the possibility that it could contribute to lysosomal pH regulation. Here we demonstrate that depleting PI(3,5)P2 by inhibiting the PIKfyve kinase causes lysosomal hyperacidification, primarily via an effect on ClC-7. We further show that PI(3,5)P2 directly inhibits ClC-7 transport and that this inhibition is eliminated in a disease-causing gain-of-function ClC-7 mutation. Together these observations suggest an intimate role for ClC-7 in lysosomal pH regulation.

biophysics↗

bioRxiv2019

The 14q32.31 DLK1-DIO3 MIR300 tumor suppressor promotes leukemogenesis by inducing cancer stem cell quiescence and inhibiting NK cell anti-cancer immunity.

Drug-resistance of tumor-initiating cells, impaired NK cell immune-response, PP2A loss-of-function and aberrant miRNA expression are cancer features resulting from microenvironmental- and tumor-specific signals. Here we report that genomic-imprinted MIR300 is a cell context-independent dual function tumor suppressor which is upregulated in quiescent leukemic stem (LSC) and NK cells by microenvironmental signals to induce quiescence and impair immune-response, respectively, but inhibited in CML and AML proliferating blasts to prevent PP2A-induced apoptosis. MIR300 anti-proliferative and PP2A-activating functions are differentially activated through dose-dependent CCND2/CDK6 and SET inhibition, respectively. LSCs escape PP2A-mediated apoptosis through TUG1 lncRNA that uncouples and limits MIR300 functions to cytostasis by regulating unbound-MIR300 levels. Halting MIR300 homeostasis restores NK cell activity and suppresses leukemic but not normal hematopoiesis by eradicating nearly all LSCs. Thus, MIR300 tumor suppressor activity is essential and therapeutically important for LSC-driven leukemias.

cancer biology↗