Angiotensin Converting Enzyme (ACE) expression in microglia reduces amyloid ß deposition and neurodegeneration by increasing SYK signaling and endolysosomal trafficking.

Genome-wide association studies (GWAS) have identified many gene polymorphisms associated with an increased risk of developing Late Onset Alzheimer's Disease (LOAD). Many of these LOAD risk-associated alleles alter disease pathogenesis by influencing microglia innate immune responses and lipid metabolism pathways. Angiotensin Converting Enzyme (ACE), a GWAS LOAD risk-associated gene best known for its role in regulating systemic blood pressure, also enhances innate immunity and lipid processing in peripheral myeloid cells, but a role for ACE in modulating the function of myeloid-derived microglia remains unexplored. Using novel mice engineered to express ACE in microglia and CNS associated macrophages (CAMs), we find that ACE expression in microglia reduces Aß plaque load, preserves vulnerable neurons and excitatory synapses, and greatly reduces learning and memory abnormalities in the 5xFAD amyloid mouse model of Alzheimer's Disease (AD). ACE-expressing microglia show enhanced Aß phagocytosis and endolysosomal trafficking, increased clustering around amyloid plaques, and increased SYK tyrosine kinase activation downstream of the major Aß receptors, TREM2 and CLEC7A. Single microglia sequencing and digital spatial profiling identifies downstream SYK signaling modules that are differentially expressed by ACE expression in microglia that mediate endolysosomal biogenesis and trafficking, mTOR and PI3K/AKT signaling, and increased oxidative phosphorylation, while pharmacologic inhibition of SYK activity in ACE-expressing microglia abrogates the potentiated Aß engulfment and endolysosomal trafficking. These findings establish a role for ACE in enhancing microglial immune function and they identify potential utility for ACE-expressing microglia as a cell-based therapy to augment endogenous microglial responses to Aß in AD.

Classical and non-classical effects of angiotensin converting enzyme: how increased ACE enhances myeloid immune function.

As part of the classical renin-angiotensin system, the peptidase angiotensin converting enzyme (ACE) makes angiotensin II which has myriad effects on systemic cardiovascular function, inflammation, and cellular proliferation. Less well known is that macrophages and neutrophils make ACE in response to immune activation which has marked effects on myeloid cell function independent of angiotensin II. Here, we discuss both classical (angiotensin) and non-classical functions of ACE and highlight mice called ACE 10/10 in which genetic manipulation increases ACE expression by macrophages and makes these mice much more resistant to models of tumors, infection, atherosclerosis, and Alzheimer's disease. In another model called NeuACE mice, neutrophils make increased ACE and these mice are much more resistant to infection. In contrast, ACE inhibitors reduce neutrophil killing of bacteria in mice and humans. Increased expression of ACE induces a marked increase in macrophage oxidative metabolism, particularly mitochondrial oxidation of lipids, secondary to increased PPARα expression, and results in increased myeloid cell ATP. ACE present in sperm has a similar metabolic effect and the lack of ACE activity in these cells reduces both sperm motility and fertilization capacity. These non-classical effects of ACE are not due to the actions of angiotensin II but to an unknown molecule, probably a peptide, that triggers a profound change in myeloid cell metabolism and function. Purifying and characterizing this peptide could offer a new treatment for several diseases and prove potentially lucrative.

Identification of retinal tau oligomers, citrullinated tau, and other tau isoforms in early and advanced AD and relations to disease status.

Importance: This study identifies and quantifies diverse pathological tau isoforms in the retina of both early and advanced-stage Alzheimer's disease (AD) and determines their relationship with disease status. Objective: A case-control study was conducted to investigate the accumulation of retinal neurofibrillary tangles (NFTs), paired helical filament (PHF)-tau, oligomeric tau (oligo-tau), hyperphosphorylated tau (p-tau), and citrullinated tau (Cit-tau) in relation to the respective brain pathology and cognitive dysfunction in mild cognitively impaired (MCI) and AD dementia patients versus normal cognition (NC) controls. Design setting and participants: Eyes and brains from donors diagnosed with AD, MCI (due to AD), and NC were collected (n=75 in total), along with clinical and neuropathological data. Brain and retinal cross-sections-in predefined superior-temporal and inferior-temporal (ST/IT) subregions-were subjected to histopathology analysis or Nanostring GeoMx digital spatial profiling. Main outcomes and measure: Retinal burden of NFTs (pretangles and mature tangles), PHF-tau, p-tau, oligo-tau, and Cit-tau was assessed in MCI and AD versus NC retinas. Pairwise correlations revealed associations between retinal and brain parameters and cognitive status. Results: Increased retinal NFTs (1.8-fold, p=0.0494), PHF-tau (2.3-fold, p<0.0001), oligo-tau (9.1-fold, p<0.0001), CitR 209 -tau (4.3-fold, p<0.0001), pSer202/Thr205-tau (AT8; 4.1-fold, p<0.0001), and pSer396-tau (2.8-fold, p=0.0015) were detected in AD patients. Retinas from MCI patients showed significant increases in NFTs (2.0-fold, p=0.0444), CitR 209 -tau (3.5-fold, p=0.0201), pSer396-tau (2.6-fold, p=0.0409), and, moreover, oligo-tau (5.8-fold, p=0.0045). Nanostring GeoMx quantification demonstrated upregulated retinal p-tau levels in MCI patients at phosphorylation sites of Ser214 (2.3-fold, p=0.0060), Ser396 (1.8-fold, p=0.0052), Ser404 (2.4-fold, p=0.0018), and Thr231 (3.3-fold, p=0.0028). Strong correlations were found between retinal tau forms to paired-brain pathology and cognitive status: a) retinal oligo-tau vs. Braak stage (r=0.60, P=0.0002), b) retinal PHF-tau vs. ABC average score (r=0.64, P=0.0043), c) retinal pSer396-tau vs. brain NFTs (r=0.68, P<0.0001), and d) retinal pSer202/Thr205-tau vs. MMSE scores (r= -0.77, P=0.0089). Conclusions and Relevance: This study reveals increases in immature and mature retinal tau isoforms in MCI and AD patients, highlighting their relationship with brain pathology and cognition. The data provide strong incentive to further explore retinal tauopathy markers that may be useful for early detection and monitoring of AD staging through noninvasive retinal imaging.

Testicular ACE regulates sperm metabolism and fertilization through the transcription factor PPARγ.

Testis angiotensin-converting enzyme (tACE) plays a critical role in male fertility, but the mechanism is unknown. By using ACE C-domain KO (CKO) mice which lack tACE activity, we found that ATP in CKO sperm was 9.4-fold lower than WT sperm. Similarly, an ACE inhibitor (ACEi) reduced ATP production in mouse sperm by 72%. Metabolic profiling showed that tACE inactivation severely affects oxidative metabolism with decreases in several Krebs cycle intermediates including citric acid, cis-aconitic acid, NAD, α-ketoglutaric acid, succinate, and L-malic acid. We found that sperms lacking tACE activity displayed lower levels of oxidative enzymes (CISY, ODO1, MDHM, QCR2, SDHA, FUMH, CPT2, and ATPA) leading to a decreased mitochondrial respiration rate. The reduced energy production in CKO sperms leads to defects in their physiological functions including motility, acrosine activity, and fertilization in vitro and in vivo. Male mice treated with ACEi show severe impairment in reproductive capacity when mated with female mice. In contrast, an angiotensin II receptor blocker (ARB) had no effect. CKO sperms express significantly less peroxisome proliferators-activated receptor gamma (PPARγ) transcription factor, and its blockade eliminates the functional differences between CKO and WT sperms, indicating PPARγ might mediate the effects of tACE on sperm metabolism. Finally, in a cohort of human volunteers, in vitro treatment with the ramipril or a PPARγ inhibitor reduced ATP production in human sperm and hence its motility and acrosine activity. These findings may have clinical significance since millions of people take ACEi daily, including men who are reproductively active.

Low booster uptake in cancer patients despite health benefits.

Patients with cancer are at increased risk of death from COVID-19 and have reduced immune responses to SARS-CoV2 vaccines, necessitating regular boosters. We performed comprehensive chart reviews, surveys of patients attitudes, serology for SARS-CoV-2 antibodies and T-cell receptor (TCR) ß sequencing for cellular responses on a cohort of 982 cancer patients receiving active cancer therapy accrued between November-3-2020 and Mar-31-2023. We found that 92·3% of patients received the primer vaccine, 70·8% received one monovalent booster, but only 30·1% received a bivalent booster. Booster uptake was lower under age 50, and among African American or Hispanic patients. Nearly all patients seroconverted after 2+ booster vaccinations (>99%) and improved cellular responses, demonstrating that repeated boosters could overcome poor response to vaccination. Receipt of booster vaccinations was associated with a lower risk of all-cause mortality (HR=0·61, P=0·024). Booster uptake in high-risk cancer patients remains low and strategies to encourage booster uptake are needed. Highlights: COVID-19 booster vaccinations increase antibody levels and maintain T-cell responses against SARS-CoV-2 in patients receiving various anti-cancer therapiesBooster vaccinations reduced all-cause mortality in patientsA significant proportion of patients remain unboosted and strategies are needed to encourage patients to be up-to-date with vaccinations.

Newt A1 cell-derived extracellular vesicles promote mammalian nerve growth.

Newts have the extraordinary ability to fully regenerate lost or damaged cardiac, neural and retinal tissues, and even amputated limbs. In contrast, mammals lack these broad regenerative capabilities. While the molecular basis of newts' regenerative ability is the subject of active study, the underlying paracrine signaling factors involved remain largely uncharacterized. Extracellular vesicles (EVs) play an important role in cell-to-cell communication via EV cargo-mediated regulation of gene expression patterns within the recipient cells. Here, we report that newt myogenic precursor (A1) cells secrete EVs (A1EVs) that contain messenger RNAs associated with early embryonic development, neuronal differentiation, and cell survival. Exposure of rat primary superior cervical ganglion (SCG) neurons to A1EVs increased neurite outgrowth, facilitated by increases in mitochondrial respiration. Canonical pathway analysis pinpointed activation of NGF/ERK5 signaling in SCG neurons exposed to A1EV, which was validated experimentally. Thus, newt EVs drive neurite growth and complexity in mammalian primary neurons.

EGR4 is critical for cell-fate determination and phenotypic maintenance of geniculate ganglion neurons underlying sweet and umami taste.

The sense of taste starts with activation of receptor cells in taste buds by chemical stimuli which then communicate this signal via innervating oral sensory neurons to the CNS. The cell bodies of oral sensory neurons reside in the geniculate ganglion (GG) and nodose/petrosal/jugular ganglion. The geniculate ganglion contains two main neuronal populations: BRN3A+ somatosensory neurons that innervate the pinna and PHOX2B+ sensory neurons that innervate the oral cavity. While much is known about the different taste bud cell subtypes, considerably less is known about the molecular identities of PHOX2B+ sensory subpopulations. In the GG, as many as 12 different subpopulations have been predicted from electrophysiological studies, while transcriptional identities exist for only 3 to 6. Importantly, the cell fate pathways that diversify PHOX2B+ oral sensory neurons into these subpopulations are unknown. The transcription factor EGR4 was identified as being highly expressed in GG neurons. EGR4 deletion causes GG oral sensory neurons to lose their expression of PHOX2B and other oral sensory genes and up-regulate BRN3A. This is followed by a loss of chemosensory innervation of taste buds, a loss of type II taste cells responsive to bitter, sweet, and umami stimuli, and a concomitant increase in type I glial-like taste bud cells. These deficits culminate in a loss of nerve responses to sweet and umami taste qualities. Taken together, we identify a critical role of EGR4 in cell fate specification and maintenance of subpopulations of GG neurons, which in turn maintain the appropriate sweet and umami taste receptor cells.

miR766-3p and miR124-3p Dictate Drug Resistance and Clinical Outcome in HNSCC.

Head and neck squamous cell carcinoma (HNSCC) is a highly aggressive disease with poor prognosis, which is mainly due to drug resistance. The biology determining the response to chemo-radiotherapy in HNSCC is poorly understood. Using clinical samples, we found that miR124-3p and miR766-3p are overexpressed in chemo-radiotherapy-resistant (non-responder) HNSCC, as compared to responder tumors. Our study shows that inhibition of miR124-3p and miR766-3p enhances the sensitivity of HNSCC cell lines, CAL27 and FaDu, to 5-fluorouracil and cisplatin (FP) chemotherapy and radiotherapy. In contrast, overexpression of miR766-3p and miR124-3p confers a resistance phenotype in HNSCC cells. The upregulation of miR124-3p and miR766-3p is associated with increased HNSCC cell invasion and migration. In a xenograft mouse model, inhibition of miR124-3p and miR766-3p enhanced the efficacy of chemo-radiotherapy with reduced growth of resistant HNSCC. For the first time, we identified that miR124-3p and miR766-3p attenuate expression of CREBRF and NR3C2, respectively, in HNSCC, which promotes aggressive tumor behavior by inducing the signaling axes CREB3/ATG5 and ß-catenin/c-Myc. Since miR124-3p and miR766-3p affect complementary pathways, combined inhibition of these two miRNAs shows an additive effect on sensitizing cancer cells to chemo-radiotherapy. In conclusion, our study demonstrated a novel miR124-3p- and miR766-3p-based biological mechanism governing treatment-resistant HNSCC, which can be targeted to improve clinical outcomes in HNSCC.

Cryobanking of Human Distal Lung Epithelial Cells for Preservation of Their Phenotypic and Functional Characteristics.

The epithelium lining airspaces of the human lung is maintained by regional stem cells, including basal cells of pseudostratified airways and alveolar type 2 (AT2) pneumocytes of the gas-exchange region. Despite effective techniques for long-term preservation of airway basal cells, procedures for efficient preservation of functional epithelial cell types of the distal gas-exchange region are lacking. Here we detail a method for cryobanking of epithelial cells from either mouse or human lung tissue for preservation of their phenotypic and functional characteristics. Flow cytometric profiling, epithelial organoid-forming efficiency, and single-cell transcriptomic analysis were used to compare cells recovered from cryobanked tissue with those of freshly dissociated tissue. AT2 cells within single-cell suspensions of enzymatically digested cryobanked distal lung tissue retained expression of the pan-epithelial marker CD326 and the AT2 cell surface antigen recognized by monoclonal antibody HT II-280, allowing antibody-mediated enrichment and downstream analysis. Isolated AT2 cells from cryobanked tissue were comparable with those of freshly dissociated tissue both in their single-cell transcriptome and their capacity for in vitro organoid formation in three-dimensional cultures. We conclude that the cryobanking method described herein allows long-term preservation of distal human lung tissue for downstream analysis of lung cell function and molecular phenotype and is ideally suited for the creation of an easily accessible tissue resource for the research community.

Longitudinal SARS-CoV-2 mRNA Vaccine-Induced Humoral Immune Responses in Patients with Cancer.

Longitudinal studies of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine-induced immune responses in patients with cancer are needed to optimize clinical care. In a prospective cohort study of 366 (291 vaccinated) patients, we measured antibody levels [anti-spike (IgG-(S-RBD) and anti-nucleocapsid immunoglobulin] at three time points. Antibody level trajectories and frequency of breakthrough infections were evaluated by tumor type and timing of treatment relative to vaccination. IgG-(S-RBD) at peak response (median = 42 days after dose 2) was higher (P = 0.002) and remained higher after 4 to 6 months (P = 0.003) in patients receiving mRNA-1273 compared with BNT162b2. Patients with solid tumors attained higher peak levels (P = 0.001) and sustained levels after 4 to 6 months (P < 0.001) compared with those with hematologic malignancies. B-cell targeted treatment reduced peak (P = 0.001) and sustained antibody responses (P = 0.003). Solid tumor patients receiving immune checkpoint inhibitors before vaccination had lower sustained antibody levels than those who received treatment after vaccination (P = 0.043). Two (0.69%) vaccinated and one (1.9%) unvaccinated patient had severe COVID-19 illness during follow-up. Our study shows variation in sustained antibody responses across cancer populations receiving various therapeutic modalities, with important implications for vaccine booster timing and patient selection. SIGNIFICANCE: Long-term studies of immunogenicity of SARS-CoV-2 vaccines in patients with cancer are needed to inform evidence-based guidelines for booster vaccinations and to tailor sequence and timing of vaccinations to elicit improved humoral responses.

An N-Cadherin 2 expressing epithelial cell subpopulation predicts response to surgery, chemotherapy and immunotherapy in bladder cancer.

Neoadjuvant chemotherapy (NAC) prior to surgery and immune checkpoint therapy (ICT) have revolutionized bladder cancer management. However, stratification of patients that would benefit most from these modalities remains a major clinical challenge. Here, we combine single nuclei RNA sequencing with spatial transcriptomics and single-cell resolution spatial proteomic analysis of human bladder cancer to identify an epithelial subpopulation with therapeutic response prediction ability. These cells express Cadherin 12 (CDH12, N-Cadherin 2), catenins, and other epithelial markers. CDH12-enriched tumors define patients with poor outcome following surgery with or without NAC. In contrast, CDH12-enriched tumors exhibit superior response to ICT. In all settings, patient stratification by tumor CDH12 enrichment offers better prediction of outcome than currently established bladder cancer subtypes. Molecularly, the CDH12 population resembles an undifferentiated state with inherently aggressive biology including chemoresistance, likely mediated through progenitor-like gene expression and fibroblast activation. CDH12-enriched cells express PD-L1 and PD-L2 and co-localize with exhausted T-cells, possibly mediated through CD49a (ITGA1), providing one explanation for ICT efficacy in these tumors. Altogether, this study describes a cancer cell population with an intriguing diametric response to major bladder cancer therapeutics. Importantly, it also provides a compelling framework for designing biomarker-guided clinical trials.

Leukemic Infiltration of Myocardium Presenting as Cardiac Arrest.

Clinically significant myocardial infiltration by leukemic cells is a rare phenomenon. We describe a case of a 47-year-old woman with newly diagnosed acute myeloid leukemia and pleuritic chest pain with rapid cardiopulmonary decompensation. Post-mortem analyses showed fibrinous pericarditis and extensive leukemic infiltration of the myocardium. (Level of Difficulty: Intermediate.).

An ACE inhibitor reduces bactericidal activity of human neutrophils in vitro and impairs mouse neutrophil activity in vivo.

Angiotensin-converting enzyme inhibitors (ACEIs) are used by millions of patients to treat hypertension, diabetic kidney disease, and heart failure. However, these patients are often at increased risk of infection. To evaluate the impact of ACEIs on immune responses to infection, we compared the effect of an ACEI versus an angiotensin receptor blocker (ARB) on neutrophil antibacterial activity. ACEI exposure reduced the ability of murine neutrophils to kill methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, and Klebsiella pneumoniae in vitro. In vivo, ACEI-treated mice infected with MRSA had increased bacteremia and tissue bacteria counts compared to mice treated with an ARB or with no drug. Similarly, ACEIs, but not ARBs, increased the incidence of MRSA-induced infective endocarditis in mice with aortic valve injury. Neutrophils from ACE knockout (KO) mice or mice treated with an ACEI produced less leukotriene B4 (LTB4) upon stimulation with MRSA or lipopolysaccharide, whereas neutrophils overexpressing ACE produced more LTB4 compared to wild-type neutrophils. As a result of reduced LTB4 production, ACE KO neutrophils showed decreased survival signaling and increased apoptosis. In contrast, neutrophils overexpressing ACE had an enhanced survival phenotype. Last, in a cohort of human volunteers receiving the ACEI ramipril for 1 week, ACEI administration reduced neutrophil superoxide and reactive oxygen species production and neutrophils isolated from volunteers during ramipril treatment had reduced bactericidal activity. Together, these data demonstrate that ACEI treatment, but not ARB treatment, can reduce the bacterial killing ability of neutrophils.

Metformin inhibition of mitochondrial ATP and DNA synthesis abrogates NLRP3 inflammasome activation and pulmonary inflammation.

Acute respiratory distress syndrome (ARDS), an inflammatory condition with high mortality rates, is common in severe COVID-19, whose risk is reduced by metformin rather than other anti-diabetic medications. Detecting of inflammasome assembly in post-mortem COVID-19 lungs, we asked whether and how metformin inhibits inflammasome activation while exerting its anti-inflammatory effect. We show that metformin inhibited NLRP3 inflammasome activation and interleukin (IL)-1ß production in cultured and alveolar macrophages along with inflammasome-independent IL-6 secretion, thus attenuating lipopolysaccharide (LPS)- and SARS-CoV-2-induced ARDS. By targeting electron transport chain complex 1 and independently of AMP-activated protein kinase (AMPK) or NF-κB, metformin blocked LPS-induced and ATP-dependent mitochondrial (mt) DNA synthesis and generation of oxidized mtDNA, an NLRP3 ligand. Myeloid-specific ablation of LPS-induced cytidine monophosphate kinase 2 (CMPK2), which is rate limiting for mtDNA synthesis, reduced ARDS severity without a direct effect on IL-6. Thus, inhibition of ATP and mtDNA synthesis is sufficient for ARDS amelioration.

Seroprevalence of antibodies to SARS-CoV-2 in healthcare workers: a cross-sectional study.

OBJECTIVE: We sought to determine the extent of SARS-CoV-2 seroprevalence and the factors associated with seroprevalence across a diverse cohort of healthcare workers. DESIGN: Observational cohort study of healthcare workers, including SARS-CoV-2 serology testing and participant questionnaires. SETTINGS: A multisite healthcare delivery system located in Los Angeles County. PARTICIPANTS: A diverse and unselected population of adults (n=6062) employed in a multisite healthcare delivery system located in Los Angeles County, including individuals with direct patient contact and others with non-patient-oriented work functions. MAIN OUTCOMES: Using Bayesian and multivariate analyses, we estimated seroprevalence and factors associated with seropositivity and antibody levels, including pre-existing demographic and clinical characteristics; potential COVID-19 illness-related exposures; and symptoms consistent with COVID-19 infection. RESULTS: We observed a seroprevalence rate of 4.1%, with anosmia as the most prominently associated self-reported symptom (OR 11.04, p<0.001) in addition to fever (OR 2.02, p=0.002) and myalgias (OR 1.65, p=0.035). After adjusting for potential confounders, seroprevalence was also associated with Hispanic ethnicity (OR 1.98, p=0.001) and African-American race (OR 2.02, p=0.027) as well as contact with a COVID-19-diagnosed individual in the household (OR 5.73, p<0.001) or clinical work setting (OR 1.76, p=0.002). Importantly, African-American race and Hispanic ethnicity were associated with antibody positivity even after adjusting for personal COVID-19 diagnosis status, suggesting the contribution of unmeasured structural or societal factors. CONCLUSION AND RELEVANCE: The demographic factors associated with SARS-CoV-2 seroprevalence among our healthcare workers underscore the importance of exposure sources beyond the workplace. The size and diversity of our study population, combined with robust survey and modelling techniques, provide a vibrant picture of the demographic factors, exposures and symptoms that can identify individuals with susceptibility as well as potential to mount an immune response to COVID-19.

The Complex Clinical and Genetic Landscape of Hereditary Peripheral Neuropathy.

Hereditary peripheral neuropathy (HPN) is a complex group of neurological disorders caused by mutations in genes expressed by neurons and Schwann cells. The inheritance of a single mutation or multiple mutations in several genes leads to disease phenotype. Patients exhibit symptoms during development, at an early age or later in adulthood. Most of the mechanistic understanding about these neuropathies comes from animal models and histopathological analyses of postmortem human tissues. Diagnosis is often very complex due to the heterogeneity and overlap in symptoms and the frequent overlap between various genes and different mutations they possess. Some symptoms in HPN are common through different subtypes such as axonal degeneration, demyelination, and loss of motor and sensory neurons, leading to similar physiologic abnormalities. Recent advances in gene-targeted therapies, genetic engineering, and next-generation sequencing have augmented our understanding of the underlying pathogenetic mechanisms of HPN.

Author Correction: Blood-brain barrier permeable nano immunoconjugates induce local immune responses for glioma therapy.

A Correction to this paper has been published: https://doi.org/10.1038/s41467-020-20129-9.

Mitochondrial pyruvate and fatty acid flux modulate MICU1-dependent control of MCU activity.

The tricarboxylic acid (TCA) cycle converts the end products of glycolysis and fatty acid ß-oxidation into the reducing equivalents NADH and FADH2 Although mitochondrial matrix uptake of Ca2+ enhances ATP production, it remains unclear whether deprivation of mitochondrial TCA substrates alters mitochondrial Ca2+ flux. We investigated the effect of TCA cycle substrates on MCU-mediated mitochondrial matrix uptake of Ca2+, mitochondrial bioenergetics, and autophagic flux. Inhibition of glycolysis, mitochondrial pyruvate transport, or mitochondrial fatty acid transport triggered expression of the MCU gatekeeper MICU1 but not the MCU core subunit. Knockdown of mitochondrial pyruvate carrier (MPC) isoforms or expression of the dominant negative mutant MPC1R97W resulted in increased MICU1 protein abundance and inhibition of MCU-mediated mitochondrial matrix uptake of Ca2+ We also found that genetic ablation of MPC1 in hepatocytes and mouse embryonic fibroblasts resulted in reduced resting matrix Ca2+, likely because of increased MICU1 expression, but resulted in changes in mitochondrial morphology. TCA cycle substrate-dependent MICU1 expression was mediated by the transcription factor early growth response 1 (EGR1). Blocking mitochondrial pyruvate or fatty acid flux was linked to increased autophagy marker abundance. These studies reveal a mechanism that controls the MCU-mediated Ca2+ flux machinery and that depends on TCA cycle substrate availability. This mechanism generates a metabolic homeostatic circuit that protects cells from bioenergetic crisis and mitochondrial Ca2+ overload during periods of nutrient stress.