Bromodomain Protein Inhibition Protects ß-Cells from Cytokine-Induced Death and Dysfunction via Antagonism of NF-κB Pathway.

Cytokine-induced ß-cell apoptosis is a major pathogenic mechanism in type 1 diabetes (T1D). Despite significant advances in understanding its underlying mechanisms, few drugs have been translated to protect ß-cells in T1D. Epigenetic modulators such as bromodomain-containing BET (bromo- and extra-terminal) proteins are important regulators of immune responses. Pre-clinical studies have demonstrated a protective effect of BET inhibitors in an NOD (non-obese diabetes) mouse model of T1D. However, the effect of BET protein inhibition on ß-cell function in response to cytokines is unknown. Here, we demonstrate that I-BET, a BET protein inhibitor, protected ß-cells from cytokine-induced dysfunction and death. In vivo administration of I-BET to mice exposed to low-dose STZ (streptozotocin), a model of T1D, significantly reduced ß-cell apoptosis, suggesting a cytoprotective function. Mechanistically, I-BET treatment inhibited cytokine-induced NF-kB signaling and enhanced FOXO1-mediated anti-oxidant response in ß-cells. RNA-Seq analysis revealed that I-BET treatment also suppressed pathways involved in apoptosis while maintaining the expression of genes critical for ß-cell function, such as Pdx1 and Ins1. Taken together, this study demonstrates that I-BET is effective in protecting ß-cells from cytokine-induced dysfunction and apoptosis, and targeting BET proteins could have potential therapeutic value in preserving ß-cell functional mass in T1D.

A metabolic-dysfunction associated steatotic liver acinus biomimetic induces pancreatic islet dysfunction in a coupled microphysiology system.

Preclinical and clinical studies suggest that lipid-induced hepatic insulin resistance is a primary defect that predisposes to dysfunction in pancreatic islets, implicating a perturbed liver-pancreas axis underlying the comorbidity of T2DM and MASLD. To investigate this hypothesis, we developed a human biomimetic microphysiological system (MPS) coupling our vascularized liver acinus MPS (vLAMPS) with primary islets on a chip (PANIS) enabling MASLD progression and islet dysfunction to be quantitatively assessed. The modular design of this system (vLAMPS-PANIS) allows intra-organ and inter-organ dysregulation to be deconvoluted. When compared to normal fasting (NF) conditions, under early metabolic syndrome (EMS) conditions, the standalone vLAMPS exhibited characteristics of early stage MASLD, while no significant differences were observed in the standalone PANIS. In contrast, with EMS, the coupled vLAMPS-PANIS exhibited a perturbed islet-specific secretome and a significantly dysregulated glucose stimulated insulin secretion (GSIS) response implicating direct signaling from the dysregulated liver acinus to the islets. Correlations between several pairs of a vLAMPS-derived and a PANIS-derived secreted factors were significantly altered under EMS, as compared to NF conditions, mechanistically connecting MASLD and T2DM associated hepatic factors with islet-derived GLP-1 synthesis and regulation. Since vLAMPS-PANIS is compatible with patient-specific iPSCs, this platform represents an important step towards addressing patient heterogeneity, identifying complex disease mechanisms, and advancing precision medicine.

Modeling mechanisms underlying differential inflammatory responses to COVID-19 in type 2 diabetes using a patient-derived microphysiological organ-on-a-chip system.

Background: COVID-19 pandemic has caused more than 6 million deaths worldwide. Co-morbid conditions such as Type 2 Diabetes (T2D) have increased mortality in COVID-19. With limited translatability of in vitro and small animal models to human disease, human organ-on-a-chip models are an attractive platform to model in vivo disease conditions and test potential therapeutics. Methods: T2D or non-diabetic patient-derived macrophages and human liver sinusoidal endothelial cells were seeded, along with normal hepatocytes and stellate cells in the liver-on-a-chip (LAMPS - liver acinus micro physiological system), perfused with media mimicking non-diabetic fasting or T2D (high levels of glucose, fatty acids, insulin, glucagon) states. The macrophages and endothelial cells were transduced to overexpress the SARS-CoV2-S (spike) protein with appropriate controls before their incorporation into LAMPS. Cytokine concentrations in the efflux served as a read-out of the effects of S-protein expression in the different experimental conditions (non-diabetic-LAMPS, T2D-LAMPS), including incubation with tocilizumab, an FDA-approved drug for severe COVID-19. Findings: S-protein expression in the non-diabetic LAMPS led to increased cytokines, but in the T2D-LAMPS, this was significantly amplified both in the number and magnitude of key pro-inflammatory cytokines (IL6, CCL3, IL1ß, IL2, TNFα, etc.) involved in cytokine storm syndrome (CSS), mimicking severe COVID-19 infection in T2D patients. Compared to vehicle control, tocilizumab (IL6-receptor antagonist) decreased the pro-inflammatory cytokine secretion in T2D-COVID-19-LAMPS but not in non-diabetic-COVID-19-LAMPS. Interpretation: macrophages and endothelial cells play a synergistic role in the pathophysiology of the hyper-inflammatory response seen with COVID-19 and T2D. The effect of Tocilizumab was consistent with large clinical trials that demonstrated Tocilizumab's efficacy only in critically ill patients with severe disease, providing confirmatory evidence that the T2D-COVID-19-LAMPS is a robust platform to model human in vivo pathophysiology of COVID-19 in T2D and for screening potential therapeutics.

The Clock-modulatory Activity of Nobiletin Suppresses Adipogenesis Via Wnt Signaling.

The circadian clock machinery exerts transcriptional control to modulate adipogenesis and its disruption leads to the development of obesity. Here, we report that Nobiletin, a circadian clock amplitude-enhancing molecule, displays antiadipogenic properties via activation of Wnt signaling pathway that is dependent on its clock modulation. Nobiletin augmented clock oscillatory amplitude with period lengthening in the adipogenic mesenchymal precursor cells and preadipocytes, accompanied by an induction of Bmal1 and clock components within the negative feedback arm. Consistent with its clock-modulatory activity, Nobiletin strongly inhibited the lineage commitment and terminal differentiation of adipogenic progenitors. Mechanistically, we show that Nobiletin induced the reactivation of Wnt signaling during adipogenesis via transcriptional up-regulation of key components within this pathway. Furthermore, Nobiletin administration in mice markedly reduced adipocyte hypertrophy, leading to a significant loss of fat mass and reduction of body weight. Last, Nobiletin inhibited the differentiation of primary preadipocytes, and this effect was dependent on a functional clock regulation. Collectively, our findings uncover a novel activity of Nobiletin in suppressing adipocyte development in a clock-dependent manner, implicating its potential application in countering obesity and associated metabolic consequences.

The clock-modulatory activity of Nobiletin suppresses adipogenesis via Wnt signaling.

The circadian clock machinery exerts transcriptional control to modulate adipogenesis and its disruption leads to the development of obesity. Here we report that Nobiletin, a clock amplitude-enhancing molecule, displays anti-adipogenic properties via activating a clock-controlled Wnt signaling pathway that suppresses adipocyte differentiation. Nobiletin augmented clock oscillation with period length shortening in the adipogenic mesenchymal precursor cells and preadipocytes, accompanied by an induction of Bmal1 and core clock components. Consistent with its circadian clock-modulatory activity, Nobiletin inhibited the lineage commitment and terminal differentiation of adipogenic progenitors. Mechanistically, we show that Nobiletin induced the re-activation of Wnt signaling during adipogenic differentiation via transcriptional up-regulation of key components of this pathway. Furthermore, Nobiletin administration in mice markedly reduced adipocyte hypertrophy, leading to a significant loss of fat mass and body weight reduction. Lastly, Nobiletin inhibited the maturation of primary preadipocytes and this effect was dependent on a functional clock regulation. Collectively, our findings uncover a novel activity of Nobiletin in suppressing adipocyte development, implicating its potential therapeutic application in countering obesity and its associated metabolic consequences.

VGLL4 and MENIN function as TEAD1 corepressors to block pancreatic ß cell proliferation.

TEAD1 and the mammalian Hippo pathway regulate cellular proliferation and function, though their regulatory function in ß cells remains poorly characterized. In this study, we demonstrate that while ß cell-specific TEAD1 deletion results in a cell-autonomous increase of ß cell proliferation, ß cell-specific deletion of its canonical coactivators, YAP and TAZ, does not affect proliferation, suggesting the involvement of other cofactors. Using an improved split-GFP system and yeast two-hybrid platform, we identify VGLL4 and MENIN as TEAD1 corepressors in ß cells. We show that VGLL4 and MENIN bind to TEAD1 and repress the expression of target genes, including FZD7 and CCN2, which leads to an inhibition of ß cell proliferation. In conclusion, we demonstrate that TEAD1 plays a critical role in ß cell proliferation and identify VGLL4 and MENIN as TEAD1 corepressors in ß cells. We propose that these could be targeted to augment proliferation in ß cells for reversing diabetes.

Circadian clock control of MRTF/SRF pathway suppresses beige adipocyte thermogenic recruitment.

The morphological transformation of adipogenic progenitors into mature adipocytes requires dissolution of actin cytoskeleton with loss of myocardin-related transcription factor (MRTF)/serum response factor (SRF) activity. Circadian clock confers temporal control in adipogenic differentiation, while the actin cytoskeleton-MRTF/SRF signaling transduces extracellular physical niche cues. Here, we define a novel circadian transcriptional control involved in actin cytoskeleton-MRTF/SRF signaling cascade that modulates beige fat thermogenic function. Key components of actin dynamic-MRTF/SRF pathway display circadian regulation in beige fat depot. The core clock regulator, brain and muscle arnt-like 1 (Bmal1), exerts direct transcriptional control of genes within the actin dynamic-MRTF/SRF cascade that impacts actin cytoskeleton organization and SRF activity. Employing beige fat-selective gene-targeting models together with pharmacological rescues, we further demonstrate that Bmal1 inhibits beige adipogenesis and thermogenic capacity in vivo via the MRTF/SRF pathway. Selective ablation of Bmal1 induces beigeing with improved glucose homeostasis, whereas its targeted overexpression attenuates thermogenic induction resulting in obesity. Collectively, our findings identify the clock-MRTF/SRF regulatory axis as an inhibitory mechanism of beige fat thermogenic recruitment with significant contribution to systemic metabolic homeostasis.

TEAD1 regulates cell proliferation through a pocket-independent transcription repression mechanism.

The Hippo-TEAD pathway regulates cellular proliferation and function. The existing paradigm is that TEAD co-activators, YAP and TAZ, and co-repressor, VGLL4, bind to the pocket region of TEAD1 to enable transcriptional activation or repressive function. Here we demonstrate a pocket-independent transcription repression mechanism whereby TEAD1 controls cell proliferation in both non-malignant mature differentiated cells and in malignant cell models. TEAD1 overexpression can repress tumor cell proliferation in distinct cancer cell lines. In pancreatic ß cells, conditional knockout of TEAD1 led to a cell-autonomous increase in proliferation. Genome-wide analysis of TEAD1 functional targets via transcriptomic profiling and cistromic analysis revealed distinct modes of target genes, with one class of targets directly repressed by TEAD1. We further demonstrate that TEAD1 controls target gene transcription in a motif-dependent and orientation-independent manner. Mechanistically, we show that TEAD1 has a pocket region-independent, direct repressive function via interfering with RNA polymerase II (POLII) binding to target promoters. Our study reveals that TEAD1 target genes constitute a mutually restricted regulatory loop to control cell proliferation and uncovers a novel direct repression mechanism involved in its transcriptional control that could be leveraged in future studies to modulate cell proliferation in tumors and potentially enhance the proliferation of normal mature cells.

Dual pancreatic adrenergic and dopaminergic signaling as a therapeutic target of bromocriptine.

Bromocriptine is approved as a diabetes therapy, yet its therapeutic mechanisms remain unclear. Though bromocriptine's actions have been mainly attributed to the stimulation of brain dopamine D2 receptors (D2R), bromocriptine also targets the pancreas. Here, we employ bromocriptine as a tool to elucidate the roles of catecholamine signaling in regulating pancreatic hormone secretion. In ß-cells, bromocriptine acts on D2R and α2A-adrenergic receptor (α2A-AR) to reduce glucose-stimulated insulin secretion (GSIS). Moreover, in α-cells, bromocriptine acts via D2R to reduce glucagon secretion. α2A-AR activation by bromocriptine recruits an ensemble of G proteins with no ß-arrestin2 recruitment. In contrast, D2R recruits G proteins and ß-arrestin2 upon bromocriptine stimulation, demonstrating receptor-specific signaling. Docking studies reveal distinct bromocriptine binding to α2A-AR versus D2R, providing a structural basis for bromocriptine's dual actions on ß-cell α2A-AR and D2R. Together, joint dopaminergic and adrenergic receptor actions on α-cell and ß-cell hormone release provide a new therapeutic mechanism to improve dysglycemia.

BMAL1 modulates ROS generation and insulin secretion in pancreatic ß-cells: An effect possibly mediated via NOX2.

The pancreatic ß cells circadian clock plays a relevant role in glucose metabolism. NADPH oxidase (NOX) family is responsible for producing reactive oxygen species (ROS), such as superoxide anion and hydrogen peroxide, using NADPH as an electron donor. In pancreatic ß-cells, NOX-derived ROS inhibits basal and glucose-stimulated insulin secretion. Thus, we hypothesized that the absence of BMAL1, a core circadian clock component, could trigger an increase of NOX2-derived ROS in pancreatic ß cells, inhibiting insulin secretion under basal and stimulated glucose conditions. To test such hypothesis, Bmal1 knockdown (KD) was performed in cultured clonal ß-cell line (INS-1E) and knocked out in isolated pancreatic islets, using a tissue-specific ß-cells Bmal1 knockout (KO) mice. The insulin secretion was assessed in the presence of NOX inhibitors. The Bmal1 KD within INS-1E cells elicited a rise of intracellular ROS content under both glucose stimuli (2.8 mM and 16.7 mM), associated with an increase in Nox2 expression. Additionally, alterations of glutathione levels, CuZnSOD and catalase activities, reduction of ATP/ADP ratio, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and aconitase activities, followed by glucokinase and Slc2a2 (Glut2) expression were also observed in INS-1E ß-cells, reflecting in a diminished insulin secretion pattern. The isolated islets from ß-cell Bmal1-/- mice have shown a similar cellular response, where an increased NOX2-derived ROS content and a reduced basal- and glucose-stimulated insulin secretion were observed. Therefore, together with NOX inhibition (Apocynin), polyethene-glycol linked to superoxide dismutase (PEG-SOD), phorbol myristate acetate (PMA), and diethyldithiocarbamate (DDC) data, our findings suggest a possible BMAL1-mediated NOX2-derived ROS generation in pancreatic ß cells, leading to the modulation of both basal- and glucose-stimulated insulin secretion.

A Quantitative Systems Pharmacology Platform Reveals NAFLD Pathophysiological States and Targeting Strategies.

Non-alcoholic fatty liver disease (NAFLD) has a high global prevalence with a heterogeneous and complex pathophysiology that presents barriers to traditional targeted therapeutic approaches. We describe an integrated quantitative systems pharmacology (QSP) platform that comprehensively and unbiasedly defines disease states, in contrast to just individual genes or pathways, that promote NAFLD progression. The QSP platform can be used to predict drugs that normalize these disease states and experimentally test predictions in a human liver acinus microphysiology system (LAMPS) that recapitulates key aspects of NAFLD. Analysis of a 182 patient-derived hepatic RNA-sequencing dataset generated 12 gene signatures mirroring these states. Screening against the LINCS L1000 database led to the identification of drugs predicted to revert these signatures and corresponding disease states. A proof-of-concept study in LAMPS demonstrated mitigation of steatosis, inflammation, and fibrosis, especially with drug combinations. Mechanistically, several structurally diverse drugs were predicted to interact with a subnetwork of nuclear receptors, including pregnane X receptor (PXR; NR1I2), that has evolved to respond to both xenobiotic and endogenous ligands and is intrinsic to NAFLD-associated transcription dysregulation. In conjunction with iPSC-derived cells, this platform has the potential for developing personalized NAFLD therapeutic strategies, informing disease mechanisms, and defining optimal cohorts of patients for clinical trials.

Inhibition of Rev-erbα ameliorates muscular dystrophy.

Duchene muscular dystrophy leads to progressive muscle structural and functional decline due to chronic degenerative-regenerative cycles. Enhancing the regenerative capacity of dystrophic muscle provides potential therapeutic options. We previously demonstrated that the circadian clock repressor Rev-erbα inhibited myogenesis and Rev-erbα ablation enhanced muscle regeneration. Here we show that Rev-erbα deficiency in the dystrophin-deficient mdx mice promotes regenerative myogenic response to ameliorate muscle damage. Loss of Rev-erbα in mdx mice improved dystrophic pathology and muscle wasting. Rev-erbα-deficient dystrophic muscle exhibit augmented myogenic response, enhanced neo-myofiber formation and attenuated inflammatory response. In mdx myoblasts devoid of Rev-erbα, myogenic differentiation was augmented together with up-regulation of Wnt signaling and proliferative pathways, suggesting that loss of Rev-erbα inhibition of these processes contributed to the improvement in regenerative myogenesis. Collectively, our findings revealed that the loss of Rev-erbα function protects dystrophic muscle from injury by promoting myogenic repair, and inhibition of its activity may have therapeutic utilities for muscular dystrophy.

Quantifying the progression of non-alcoholic fatty liver disease in human biomimetic liver microphysiology systems with fluorescent protein biosensors.

Metabolic syndrome is a complex disease that involves multiple organ systems including a critical role for the liver. Non-alcoholic fatty liver disease (NAFLD) is a key component of the metabolic syndrome and fatty liver is linked to a range of metabolic dysfunctions that occur in approximately 25% of the population. A panel of experts recently agreed that the acronym, NAFLD, did not properly characterize this heterogeneous disease given the associated metabolic abnormalities such as type 2 diabetes mellitus (T2D), obesity, and hypertension. Therefore, metabolic dysfunction-associated fatty liver disease (MAFLD) has been proposed as the new term to cover the heterogeneity identified in the NAFLD patient population. Although many rodent models of NAFLD/NASH have been developed, they do not recapitulate the full disease spectrum in patients. Therefore, a platform has evolved initially focused on human biomimetic liver microphysiology systems that integrates fluorescent protein biosensors along with other key metrics, the microphysiology systems database, and quantitative systems pharmacology. Quantitative systems pharmacology is being applied to investigate the mechanisms of NAFLD/MAFLD progression to select molecular targets for fluorescent protein biosensors, to integrate computational and experimental methods to predict drugs for repurposing, and to facilitate novel drug development. Fluorescent protein biosensors are critical components of the platform since they enable monitoring of the pathophysiology of disease progression by defining and quantifying the temporal and spatial dynamics of protein functions in the biosensor cells, and serve as minimally invasive biomarkers of the physiological state of the microphysiology system experimental disease models. Here, we summarize the progress in developing human microphysiology system disease models of NAFLD/MAFLD from several laboratories, developing fluorescent protein biosensors to monitor and to measure NAFLD/MAFLD disease progression and implementation of quantitative systems pharmacology with the goal of repurposing drugs and guiding the creation of novel therapeutics.

Dopamine regulates pancreatic glucagon and insulin secretion via adrenergic and dopaminergic receptors.

Dopamine (DA) and norepinephrine (NE) are catecholamines primarily studied in the central nervous system that also act in the pancreas as peripheral regulators of metabolism. Pancreatic catecholamine signaling has also been increasingly implicated as a mechanism responsible for the metabolic disturbances produced by antipsychotic drugs (APDs). Critically, however, the mechanisms by which catecholamines modulate pancreatic hormone release are not completely understood. We show that human and mouse pancreatic α- and ß-cells express the catecholamine biosynthetic and signaling machinery, and that α-cells synthesize DA de novo. This locally-produced pancreatic DA signals via both α- and ß-cell adrenergic and dopaminergic receptors with different affinities to regulate glucagon and insulin release. Significantly, we show DA functions as a biased agonist at α2A-adrenergic receptors, preferentially signaling via the canonical G protein-mediated pathway. Our findings highlight the interplay between DA and NE signaling as a novel form of regulation to modulate pancreatic hormone release. Lastly, pharmacological blockade of DA D2-like receptors in human islets with APDs significantly raises insulin and glucagon release. This offers a new mechanism where APDs act directly on islet α- and ß-cell targets to produce metabolic disturbances.

Light-Dark Patterns Mirroring Shift Work Accelerate Atherosclerosis and Promote Vulnerable Lesion Phenotypes.

Background Despite compelling epidemiological evidence that circadian disruption inherent to long-term shift work enhances atherosclerosis progression and vascular events, the underlying mechanisms remain poorly understood. A challenge to the use of mouse models for mechanistic and interventional studies involving light-dark patterns is that the spectral and absolute sensitivities of the murine and human circadian systems are very different, and light stimuli in nocturnal mice should be scaled to represent the sensitivities of the human circadian system. Methods and Results We used calibrated devices to deliver to low-density lipoprotein receptor knockout mice light-dark patterns representative of that experienced by humans working day shifts or rotating shift schedules. Mice under day shifts were maintained under regular 12 hours of light and 12 hours of dark cycles. Mice under rotating shift schedules were subjected for 11 weeks to reversed light-dark patterns 4 days in a row per week, followed by 3 days of regular light-dark patterns. In both protocols the light phases consisted of monochromatic green light at an irradiance of 4 µW/cm2. We found that the shift work paradigm disrupts the foam cell's molecular clock and increases endoplasmic reticulum stress and apoptosis. Lesions of mice under rotating shift schedules were larger and contained less prostabilizing fibrillar collagen and significantly increased areas of necrosis. Conclusions Low-density lipoprotein receptor knockout mice under light-dark patterns analogous to that experienced by rotating shift workers develop larger and more vulnerable plaques and may represent a valuable model for further mechanistic and/or interventional studies against the deleterious vascular effects of rotating shift work.

Chronic circadian shift leads to adipose tissue inflammation and fibrosis.

The circadian clock exerts temporal coordination of metabolic pathways. Clock disruption is intimately linked with the development of obesity and insulin resistance, and our previous studies found that the essential clock transcription activator, Brain and Muscle Arnt-like 1 (Bmal1), is a key regulator of adipogenesis. However, the metabolic consequences of chronic shiftwork on adipose tissues have not been clearly defined. Here, using an environmental lighting-induced clock disruption that mimics rotating shiftwork schedule, we show that chronic clock dysregulation for 6 months in mice resulted in striking adipocyte hypertrophy with adipose tissue inflammation and fibrosis. Both visceral and subcutaneous depots display enlarged adipocyte with prominent crown-like structures indicative of macrophage infiltration together with evidence of extracellular matrix remodeling. Global transcriptomic analyses of these fat depots revealed that shiftwork resulted in up-regulations of inflammatory, adipogenic and angiogenic pathways with disruption of normal time-of-the-day-dependent regulation. These changes in adipose tissues are associated with impaired insulin signaling in mice subjected to shiftwork, together with suppression of the mTOR signaling pathway. Taken together, our study identified the significant adipose depot dysfunctions induced by chronic shiftwork regimen that may underlie the link between circadian misalignment and insulin resistance.

SRF-MRTF signaling suppresses brown adipocyte development by modulating TGF-ß/BMP pathway.

The SRF/MRTF and upstream signaling cascade play key roles in actin cytoskeleton organization and myocyte development. To date, how this signaling axis may function in brown adipocyte lineage commitment and maturation has not been delineated. Here we report that MRTF-SRF signaling exerts inhibitory actions on brown adipogenesis, and suppressing this negative regulation promotes brown adipocyte lineage development. During brown adipogenic differentiation, protein expressions of SRF, MRTFA/B and its transcription targets were down-regulated, and MRTFA/B shuttled from nucleus to cytoplasm. Silencing of SRF or MRTF-A/MRTF-B enhanced two distinct stages of brown adipocyte development, mesenchymal stem cell determination to brown adipocytes and terminal differentiation of brown adipogenic progenitors. We further demonstrate that the MRTF-SRF axis exerts transcriptional regulations of the TGF-ß and BMP signaling pathway, critical developmental cues for brown adipocyte development. TGF-ß signaling activity was significantly attenuated, whereas that of the BMP pathway augmented by inhibition of SRF or MRTF-A/MRTF-B, leading to enhanced brown adipocyte differentiation. Our study demonstrates the MRTF-SRF transcriptional cascade as a negative regulator of brown adipogenesis, through its transcriptional control of the TGF-ß/BMP signaling pathways.

Tead1 is essential for mitochondrial function in cardiomyocytes.

Mitochondrial dysfunction occurs in most forms of heart failure. We have previously reported that Tead1, the transcriptional effector of Hippo pathway, is critical for maintaining adult cardiomyocyte function, and its deletion in adult heart results in lethal acute dilated cardiomyopathy. Growing lines of evidence indicate that Hippo pathway plays a role in regulating mitochondrial function, although its role in cardiomyocytes is unknown. Here, we show that Tead1 plays a critical role in regulating mitochondrial OXPHOS in cardiomyocytes. Assessment of mitochondrial bioenergetics in isolated mitochondria from adult hearts showed that loss of Tead1 led to a significant decrease in respiratory rates, with both palmitoylcarnitine and pyruvate/malate substrates, and was associated with reduced electron transport chain complex I activity and expression. Transcriptomic analysis from Tead1-knockout myocardium revealed genes encoding oxidative phosphorylation, TCA cycle, and fatty acid oxidation proteins as the top differentially enriched gene sets. Ex vivo loss of function of Tead1 in primary cardiomyocytes also showed diminished aerobic respiration and maximal mitochondrial oxygen consumption capacity, demonstrating that Tead1 regulation of OXPHOS in cardiomyocytes is cell autonomous. Taken together, our data demonstrate that Tead1 is a crucial transcriptional node that is a cell-autonomous regulator, a large network of mitochondrial function and biogenesis related genes essential for maintaining mitochondrial function and adult cardiomyocyte homeostasis.NEW & NOTEWORTHY Mitochondrial dysfunction constitutes an important aspect of heart failure etiopathogenesis and progression. However, the molecular mechanisms are still largely unknown. Growing lines of evidence indicate that Hippo-Tead pathway plays a role in cellular bioenergetics. This study reveals the novel role of Tead1, the downstream transcriptional effector of Hippo pathway, as a novel regulator of mitochondrial oxidative phosphorylation and in vivo cardiomyocyte energy metabolism, thus providing a potential therapeutic target for modulating mitochondrial function and enhancing cytoprotection of cardiomyocytes.

Metabolic-sensing of the skeletal muscle clock coordinates fuel oxidation.

Circadian clock confers temporal control in metabolism, with its disruption leading to the development of insulin resistance. Metabolic substrate utilization in skeletal muscle is coordinated with diurnal nutrient cycles. However, whether the molecular clock is involved in this coordination is largely unknown. Using a myocyte-selective genetic ablation mouse model of the essential clock activator Bmal1, here we identify muscle-intrinsic clock as a sensor of feeding cues to orchestrate skeletal muscle oxidation required for global nutrient flux. Bmal1 in skeletal muscle responds robustly to feeding in vivo and insulin induces its expression. Muscle Bmal1 deficiency impaired the transcriptional control of glucose metabolic pathway, resulting in markedly attenuated glucose utilization and fasting hyperglycemia. Notably, the loss of Bmal1 response to feeding abolished fasting-to-feeding metabolic fuel switch from fatty acids to glucose in skeletal muscle, leading to the activation of energy-sensing pathways for fatty acid oxidation. These altered metabolic substrate oxidations in Bmal1-deficient muscle ultimately depleted circulating lipid levels that prevented hepatic steatosis. Collectively, our findings highlight the key role of the metabolic-sensing function of skeletal muscle clock in partitioning nutrient flux between muscle and liver to maintain whole-body lipid and glucose homeostasis.