Biology subjects

Sack, M. N.

Publications and source records attributed to Sack, M. N..

7 recordsLinked to original sources

bioRxiv2026

SIRT5-dependent regulation of ASL controls arginine metabolism and T cell function

NAD supplementation blunts Th1 and Th17 inflammation, in part, through arginine metabolism-dependent regulation of mitochondrial energetics, redox balance and signal transduction. Whether the NAD+-dependent sirtuin deacylases contribute to this regulation is unknown. Here, we show that both SIRT1 and SIRT5 transcript levels are induced in CD4+ T cells in human participants following oral supplementation of the NAD+ precursor nicotinamide riboside (NR). Among the sirtuin family members, SIRT5 rather than SIRT1 emerged as the predominant regulator of arginine and fumarate metabolism. Genetic depletion or pharmacologic inhibition of SIRT5 attenuated NR-mediated increases in arginine and fumarate and abolished the anti-inflammatory -effects of NR on Th1 and Th17 cytokine production. In contrast, the responses to exogenous arginine or citrulline supplementation were preserved, indicating that SIRT5 functions upstream of arginine biosynthesis. Metabolomic profiling further demonstrated that SIRT5 is required for NR-induced remodeling of the arginine biosynthetic pathway. Mechanistically, SIRT5 physically interacted with arginosuccinate lyase (ASL), promoted ASL-dependent arginine accumulation, and regulated ASL post-translational acylation, including glutarylation and malonylation. Loss of SIRT5 disrupted NR-mediated redox homeostasis, antioxidant gene expression, and cytokine suppression. Collectively, these findings identify SIRT5 as a critical mediator of NAD precursor-induced metabolic remodeling that links ASL-dependent arginine metabolism to redox balance and effector function in human CD4 T cells.

immunology↗

bioRxiv2026

BLOC1S1 regulates autolysosomal and exosomal dynamics during CD4⁺ T cell differentiation

Although the endolysosome system is central to intracellular recycling, signal transduction, and intercellular communication via exocytosis, its role in immunoregulation remains incompletely defined. We recently identified that CD4+ T cell-specific depletion of BLOC1S1, a component of multiprotein complexes regulating endolysosomal biology, predisposes toward type 2 (Th2) immunity. We therefore hypothesized that the study of BLOC1S1-deficient CD4+ T cells would expand our understanding of endolysosomal dynamics in Th2 function. Here, we demonstrate that CD4+ T cell BLOC1S1 deficiency resulted in aberrant lysosomal distribution, accumulation of endosomal vesicles, and increased exocytosis, which collectively correlated with enhanced Th2 immune responses. The phenotype was associated with upregulation of key components of the exocytosis machinery, including RAB11 and VAMP7. Functional inhibition of these vesicle trafficking proteins following siRNA knockdown of RAB11 and VAMP7 significantly attenuated Th2 cytokine secretion in BLOC1S1-deficient CD4+ T cells, highlighting their essential role in exosome-mediated cytokine export. Furthermore, exosomes derived from BLOC1S1-deficient CD4+ T cells promoted Th2 polarization in recipient cells, indicating a mechanism of intracellular amplification. Together, these findings identify BLOC1S1 as a critical regulator of lysosomal dynamics and exocytic vesicle fusion, thereby linking intracellular trafficking mechanisms to Th2 immune regulation.

immunology↗

bioRxiv2026

ISG15 orchestrates dynamic crosstalk between mitochondrial fat oxidation and type 1 interferon in myeloid cells

In contrast to Krebs cycle intermediates, the role of mitochondrial fatty acid oxidation (FAO) in immunometabolism remains incompletely characterized. Studying primary bone marrow-derived macrophages (BMDMs), we show that IFN-{beta} and STING activation augments FAO and associated enzymes carnitine palmitoyltransferase 1a (CPT1a) and acetyl-CoA acetyltransferase 1 (ACAT1). Depleting BMDM Cpt1a reduces FAO and dampens type 1 interferon (IFN) signaling due to decreased histone H3-K9/K14 acetylation, supporting the prior finding of an epigenetic role of FAO in sustaining type 1 IFN. Interestingly, FAO induction by IFN was dynamic as a heightened IFN response suppressed FAO, suggesting a concurrent negative-feedback mechanism. This FAO blunting correlated with increased expression of interferon-stimulated gene 15 (ISG15), a ubiquitin-like modifier known to modulate metabolic proteins through ISGylation. This immune-metabolic signature was similarly operational in mice infected with lymphocytic choriomenigitis virus (LCMV) with temporal discordance between ISG15 levels and FAO. The role of ISG15 in this negative feedback was shown with increased FAO and type 1 IFN response in Isg15 knockout BMDMs. Parallely, endogenous co-immunoprecipitation showed interactions between ISG15 and CPT1a/ACAT1. This ISG15-FAO regulatory interaction was also evident in systemic lupus erythematosus (SLE)-associated interferonopathy and in primary monocytes from SLE individuals that exhibited increased ISG15 levels and reduced FAO rates. Collectively, these findings support a model in which type 1 IFN initially enhances FAO to amplify interferon production, but excessive IFN-signaling induces ISG15-mediated inhibition of FAO, a putative feedback loop that restrains inflammation and preserves immune homeostasis. Together these data identify a novel biphasic FAO-dependent immunometabolic regulatory program. Graphical Summary O_FIG O_LINKSMALLFIG WIDTH=190 HEIGHT=200 SRC="FIGDIR/small/700051v1_ufig1.gif" ALT="Figure 1"> View larger version (48K): org.highwire.dtl.DTLVardef@13f572eorg.highwire.dtl.DTLVardef@174b6aeorg.highwire.dtl.DTLVardef@1856483org.highwire.dtl.DTLVardef@89e5a6_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIType 1 IFN rewires myeloid cell metabolism towards FAO. C_LIO_LIFAO epigenetically fuels Type 1 1IFN response. C_LIO_LIEffect of IFN on FAO is dynamic: inducing FAO at low concentrations while suppressing it during a heightened IFN response. C_LIO_LIEnhanced Type 1 IFN response produces ISG15 which ISGylates key enzymes of FAO altering their stability C_LIO_LIISG15 negatively regulates FAO to control Type 1 IFN homeostasis in a negative feedback loop. C_LI

immunology↗

bioRxiv2024

BLOC1S1 control of vacuolar organelle fidelity modulates TH2 cell immunity and allergy susceptibility.

The levels of biogenesis of lysosome organelles complex 1 subunit 1 (BLOC1S1) control mitochondrial and endolysosome organelle homeostasis and function. Reduced fidelity of these vacuolar organelles is increasingly being recognized as important in instigating cell-autonomous immune cell activation. We reasoned that exploring the role of BLOC1S1 in CD4+ T cells, may further advance our understanding of regulatory events linked to mitochondrial and/or endolysosomal function in adaptive immunity. Transcript levels of the canonical transcription factors driving CD4+T cell polarization in response to activation showed that, the TH2 regulator GATA3 and phosphorylated STAT6 were preferentially induced in BLOC1S1 depleted primary CD4+ T (TKO) cells. In parallel, in response to both T cell receptor activation and in response to TH2 polarization the levels of IL-4, IL-5 and IL-13 were markedly induced in the absence of BLOC1S1. At the organelle level, mitochondrial DNA leakage evoked cGAS-STING and NF-kB pathway activation with subsequent TH2 polarization. The induction of autophagy with rapamycin reduced cytosolic mtDNA and reverses these TH2 signatures. Furthermore, genetic knockdown of STING and STING and NF-{kappa}B inhibition ameliorated this immune regulatory cascade in TKO cells. Finally, at a functional level, TKO mice displayed increased susceptible to allergic conditions including atopic dermatitis and allergic asthma. In conclusion, BLOC1S1 depletion mediated disruption of mitochondrial integrity to initiate a predominant TH2 responsive phenotype via STING-NF-{kappa}B driven signaling of the canonical TH2 regulatory program.

immunology↗

bioRxiv2024

The mitochondrial thiolase ACAT1 regulates monocyte/macrophage type I interferon via epigenetic control.

Lipid-derived acetyl-CoA is shown to be the major carbon source for histone acetylation. However, there is no direct evidence demonstrating lipid metabolic pathway contribututions to this process. Mitochondrial acetyl-CoA acetyltransferase 1 (ACAT1) catalyzes the final step of {beta}-oxidation, the aerobic process catabolizing fatty acids (FA) into acetyl-CoA. To investigate this in the context of immunometabolism, we generated macrophage cell line lacking ACAT1. 13C-carbon tracing combined with mass spectrometry confirmed incorporation of FA-derived carbons into histone H3 and this incorporation was reduced in ACAT1 KO macrophage cells. RNA-seq identified a subset of genes downregulated in ACAT1 KO cells including STAT1/2 and interferon stimulated genes (ISGs). CHIP analysis demonstrated reduced acetyl-H3 binding to STAT1 promoter/enhancer regions. Increasing histone acetylation rescued STAT1/2 expression in ACAT1 KO cells. Concomitantly, ligand triggered IFN{beta} release was blunted in ACAT1 KO cells and rescued by reconstitution of ACAT1. Furthermore, ACAT1 promotes FA-mediated histone acetylation in an acetylcarnitine shuttle-dependent manner. In patients with obesity, levels of ACAT1 and histone acetylation are abnormally elevated. Thus, our study identified a novel link between ACAT1 mediated FA metabolism and epigenetic modification on STAT1/2 that uncovers a regulatory role of lipid metabolism in innate immune signaling and opens novel avenues for interventions in human diseases such as obesity.

immunology↗

bioRxiv2022

Reduced acetylation of TFAM promotes bioenergetic dysfunction in the failing heart

General Control of Amino-Acid Synthesis 5-like 1 (GCN5L1) was previously identified as a key regulator of protein lysine acetylation in mitochondria. Subsequent studies demonstrated that GCN5L1 regulates the acetylation status and activity of mitochondrial fuel substrate metabolism enzymes. However, the role of GCN5L1 in response to chronic hemodynamic stress is largely unknown. Here, we show that cardiomyocyte-specific GCN5L1 knockout mice (cGCN5L1 KO) display exacerbated pressure overload-induced heart failure progression following transaortic constriction (TAC). Mitochondrial DNA and mitochondrial electron transport chain protein levels were decreased in cGCN5L1 KO hearts after TAC, and isolated neonatal cardiomyocytes with reduced GCN5L1 expression had lower bioenergetic output in response to hypertrophic stress. Loss of GCN5L1 expression led to a decrease in the acetylation status of mitochondrial transcription factor A (TFAM) after TAC in vivo, which was linked to a reduction in mtDNA levels in vitro. Together, these data suggest that GCN5L1 may protect from hemodynamic stress by maintaining mitochondrial bioenergetic output. HighlightsO_LIReduced GCN5L1 expression in the failing heart promotes contractile dysfunction C_LIO_LIMitochondrial DNA (mtDNA) levels are reduced in cardiomyocyte-specific GCN5L1 knockout mice following hemodynamic stress C_LIO_LIGCN5L1 knockdown reduces, and GCN5L1 overexpression increases, bioenergetic output in hypertrophic cardiomyocytes C_LIO_LIGCN5L1-mediated acetylation of TFAM promotes increased mtDNA levels C_LI

physiology↗

bioRxiv2019

Cardiomyocyte-Specific Deletion of GCN5L1 Limits Cardiac Contractile Decline in Obese Pre-Diabetic Mice

Reduced substrate flexibility, and a shift towards increased cardiac fatty acid utilization, is a key feature of obesity and diabetes. We previously reported that increased acetylation of several mitochondrial FAO enzymes, regulated in part via increased abundance of the mitochondrial acetyltransferase GCN5L1, correlated with increased FAO enzyme activity in the heart. The focus of the current study was to investigate whether decreased acetylation, via cardiomyocyte-specific deletion of GCN5L1 (GCN5L1 cKO), regulates cardiac energy metabolism following exposure to a high fat diet (HFD). Excess dietary fat led to similar cardiac hypertrophy in wildtype and GCN5L1 cKO mice. We show that acetylation of pyruvate dehydrogenase (PDH) was significantly reduced in HFD GCN5L1 cKO hearts, which correlated with its increased enzymatic activity relative to HFD wildtype controls. The acetylation of both electron transport chain Complex I protein NDUFB8, and manganese superoxide dismutase 2 (SOD2), was significantly reduced by GCN5L1 deletion in HFD animals, resulting in decreased lipid peroxidation. Finally, we show that in contrast to wildtype mice, GCN5L1 cKO hearts maintain ex vivo contractility and workload in response to a HFD. In summary, we show that GCN5L1 deletion limits cardiac functional decline observed in HFD mice, by increasing fuel substrate flexibility and limiting reactive oxygen species damage.

physiology↗