FoxP1 Represses MEF2A in Striated Muscle.

Myocyte enhancer factor 2 (MEF2) proteins are involved in multiple developmental, physiological, and pathological processes in vertebrates. Protein-protein interactions underlie the plethora of biological processes impacted by MEF2A, necessitating a detailed characterization of the MEF2A interactome. A nanobody based affinity-purification/mass spectrometry strategy was employed to achieve this goal. Specifically, the MEF2A protein complexes were captured from myogenic lysates using a GFP-tagged MEF2A protein immobilized with a GBP-nanobody followed by LC-MS/MS proteomic analysis to identify MEF2A interactors. After bioinformatic analysis, we further characterized the interaction of MEF2A with a transcriptional repressor, FOXP1. FOXP1 coprecipitated with MEF2A in proliferating myogenic cells which diminished upon differentiation (myotube formation). Ectopic expression of FOXP1 inhibited MEF2A driven myogenic reporter genes (derived from the creatine kinase muscle and myogenin genes) and delayed induction of endogenous myogenin during differentiation. Conversely, FOXP1 depletion enhanced MEF2A transactivation properties and myogenin expression. The FoxP1:MEF2A interaction is also preserved in cardiomyocytes and FoxP1 depletion enhanced cardiomyocyte hypertrophy. FOXP1 prevented MEF2A phosphorylation and activation by the p38MAPK pathway. Overall, these data implicate FOXP1 in restricting MEF2A function in order to avoid premature differentiation in myogenic progenitors and also to possibly prevent re-activation of embryonic gene expression in cardiomyocyte hypertrophy.

The MEF2A transcription factor interactome in cardiomyocytes.

Transcriptional regulators encoded by the Myocyte Enhancer Factor 2 (MEF2) gene family play a fundamental role in cardiac development, homeostasis and pathology. Previous studies indicate that MEF2A protein-protein interactions serve as a network hub in several cardiomyocyte cellular processes. Based on the idea that interactions with regulatory protein partners underly the diverse roles of MEF2A in cardiomyocyte gene expression, we undertook a systematic unbiased screen of the MEF2A protein interactome in primary cardiomyocytes using an affinity purification-based quantitative mass spectrometry approach. Bioinformatic processing of the MEF2A interactome revealed protein networks involved in the regulation of programmed cell death, inflammatory responses, actin dynamics and stress signaling in primary cardiomyocytes. Further biochemical and functional confirmation of specific protein-protein interactions documented a dynamic interaction between MEF2A and STAT3 proteins. Integration of transcriptome level data from MEF2A and STAT3-depleted cardiomyocytes reveals that the balance between MEF2A and STAT3 activity exerts a level of executive control over the inflammatory response and cardiomyocyte cell survival and experimentally ameliorates Phenylephrine induced cardiomyocyte hypertrophy. Lastly, we identified several MEF2A/STAT3 co-regulated genes, including the MMP9 gene. Herein, we document the cardiomyocyte MEF2A interactome, which furthers our understanding of protein networks involved in the hierarchical control of normal and pathophysiological cardiomyocyte gene expression in the mammalian heart.

Re-organization of nucleolar architecture in myogenic differentiation.

Myogenesis, the process of muscle differentiation, requires an extensive remodeling of the cellular transcriptome and proteome. Whereas the transcriptional program underpinning myogenesis is well characterized, the required adaptation in protein synthesis is incompletely understood. Enhanced protein synthesis necessitates ribosome biogenesis at the nucleolus. Nucleolar size and activity are inextricably linked with altered gene expression. Here, we report changes in nucleolar morphology and function during myogenic differentiation. Immunofluorescence analysis revealed alterations in nucleolar morphology that were dependent on the cellular state - proliferative or quiescent myogenic progenitors (myoblasts or reserve cells) contained multiple small nucleoli with a characteristic spherical shape, whereas multinucleated myotubes typically contained one large, often irregularly shaped nucleolus. These morphological alterations are consistent with changes to nucleolar phase separation properties. Re-organization of the nucleolar structure was correlated with enhanced rRNA production and protein translation. Inhibition of mTOR signaling with rapamycin perturbed nucleolar re-organization. Conversely, hyperactivated mTOR enhanced alterations in nucleolar morphology. These findings support the idea that there is an mTOR dependent re-organization of nucleolar structure during myogenesis, enhancing our understanding of myogenesis and possibly facilitating new approaches to therapeutic interventions in muscle pathologies.

MEF2 in cardiac hypertrophy in response to hypertension.

Hypertension is a globally prevalent pathological condition and an underlying risk factor for the development of cardiac hypertrophy leading to heart failure. Myocyte enhancer factor 2 (Mef2) has been identified as one of the primary effectors of morphological changes in the hypertensive heart, as part of a complex network of molecular signaling controlling cardiac gene expression. Experimental chronic pressure-overload models that mimic hypertension in the mammalian heart lead to the activation of various pathological mechanisms that result in structural changes leading to debilitating cardiac hypertrophy and ultimately heart failure. The purpose here is to survey the literature implicating Mef2 in hypertension induced cardiac hypertrophy, towards illuminating points of interest for understanding and potentially treating heart failure.

The importance of biological sex in cardiac cachexia.

Cardiac cachexia is a catabolic muscle-wasting syndrome observed in approximately 1 in 10 patients with heart failure. Increased skeletal muscle atrophy leads to frailty and limits mobility, which impacts quality of life, exacerbates clinical care, and is associated with higher rates of mortality. Heart failure is known to exhibit a wide range of prevalence and severity when examined across individuals of different ages and with comorbidities related to diabetes, renal failure, and pulmonary dysfunction. It is also recognized that men and women exhibit striking differences in the pathophysiology of heart failure, as well as skeletal muscle homeostasis. Given that both skeletal muscle and heart failure physiology are in part sex-dependent, the diagnosis and treatment of cachexia in patients with heart failure may depend on a comprehensive examination of how these organs interact. In this review, we explore the potential for sex-specific differences in cardiac cachexia. We summarize advantages and disadvantages of clinical methods used to measure muscle mass and function and provide alternative measurements that should be considered in preclinical studies. In addition, we summarize sex-dependent effects on muscle wasting in preclinical models of heart failure, disuse, and cancer. Lastly, we discuss the endocrine function of the heart and outline unanswered questions that could directly impact patient care.

TAZ exhibits phase separation properties and interacts with Smad7 and ß-catenin to repress skeletal myogenesis.

Hippo signaling in Drosophila and mammals is prominent in regulating cell proliferation, death and differentiation. Hippo signaling effectors (YAP and TAZ; also known as YAP1 and WWTR1, respectively) exhibit crosstalk with transforming growth factor-ß (TGF-ß)-Smad and Wnt/ß-catenin pathways. Previously, we implicated Smad7 and ß-catenin in mammalian myogenesis. Therefore, we assessed a potential role of TAZ on the Smad7-ß-catenin complex in muscle cells. Here, we document functional interactions between Smad7, TAZ and ß-catenin in mouse myogenic cells. Ectopic TAZ expression resulted in repression of the muscle-specific creatine kinase muscle (Ckm) gene promoter and its corresponding protein level. Depletion of endogenous TAZ enhanced Ckm promoter activation. Ectopic TAZ, while potently active on a TEAD reporter (HIP-HOP), repressed myogenin (Myog) and Myod1 enhancer regions and myogenin protein level. Additionally, a Wnt/ß-catenin readout (TOP flash) demonstrated TAZ-mediated inhibition of ß-catenin activity. In myoblasts, TAZ was predominantly localized in nuclear speckles, while in differentiation conditions TAZ was hyperphosphorylated at Ser89, leading to enhanced cytoplasmic sequestration. Finally, live-cell imaging indicated that TAZ exhibits properties of liquid-liquid phase separation (LLPS). These observations indicate that TAZ, as an effector of Hippo signaling, suppresses the myogenic differentiation machinery.

Nucleolar localization of c-Jun.

Nucleoli are well defined for their function in ribosome biogenesis, but only a small fraction of the nucleolar proteome has been characterized. Here, we report that the proto-oncogene, c-Jun, is targeted to the nucleolus. Using live cell imaging in myogenic cells, we document that the c-Jun basic domain contains a unique, evolutionarily conserved motif that determines nucleolar targeting. Fos family Jun dimer partners, such as Fra2, while nuclear, do not co-localize with c-Jun in the nucleolus. A point mutation in c-Jun that mimics Fra2 (M260E) in its Nucleolar Localization sequence (NoLS) results in loss of c-Jun nucleolar targeting while still preserving nuclear localization. Fra2 can sequester c-Jun in the nucleoplasm, indicating that the stoichiometric ratio of heterodimeric partners regulates c-Jun nucleolar targeting. Finally, nucleolar localization of c-Jun modulates nucleolar architecture and ribosomal RNA accumulation. These studies highlight a novel role for Jun family proteins in the nucleolus, having potential implications for a diverse array of AP-1-regulated cellular processes.

Identification of the Most Important Subset of Doppler, Laboratory, and Clinical Parameters for Serial TIPS Evaluation.

OBJECTIVE. The purpose of the present study was to identify the subset of a wide range of serial Doppler, laboratory, and clinical parameters most predictive (both individually and in combination) of TIPS dysfunction in a large patient sample. MATERIALS AND METHODS. The medical records of 189 patients who had undergone TIPS procedures were analyzed. The patients (mean age, 52 years; 62% of whom were men) had undergone 1139 Doppler studies and 323 portovenograms. Laboratory parameters included model for end-stage liver disease (MELD) scores, serum albumin levels, presence of ascites, and time since last intervention. Doppler parameters included intrashunt velocities, temporal change in intrashunt velocities, main portal vein velocity, direction of flow in the left portal hepatic vein, and venous pulsatility index. Statistical analysis used ROC, univariate, and multivariate regression models to assess the parameters both individually and in combination. Shunt dysfunction was defined by a portosystemic gradient of more than 12 mm Hg. RESULTS. The laboratory and clinical parameters of greatest predictive value included the MELD score and the time since the last intervention. The Doppler parameters that were of greatest predictive value included the change in velocity at the hepatic venous end and the left portal vein flow direction. Multivariate models produced an AUC of 0.74. Differences between functional and dysfunctional shunts were also statistically significant for absolute velocity at the hepatic venous end, the change in velocity within the stent, and the temporal change in the mid shunt velocity. CONCLUSION. The subset of serial parameters most predictive of TIPS dysfunction are the temporal change in the velocity at the hepatic venous end, the absolute velocity at the hepatic venous end, the direction of flow in the left portal venous branch, and changes in the MELD score.

Maintenance of the Undifferentiated State in Myogenic Progenitor Cells by TGFß Signaling is Smad Independent and Requires MEK Activation.

Transforming growth factor ß (TGFß) is a pluripotent cytokine and regulates a myriad of biological processes. It has been established that TGFß potently inhibits skeletal muscle differentiation; however, the molecular mechanism is not clearly defined. Previously, we reported that inhibition of the TGFß canonical pathway by an inhibitory Smad, Smad7, does not reverse this effect on differentiation, suggesting that activation of receptor Smads (R-Smads) by TGFß is not responsible for repression of myogenesis. In addition, pharmacological blockade of Smad3 activation by TGFß did not reverse TGFß's inhibitory effect on myogenesis. In considering other pathways, we observed that TGFß potently activates MEK/ERK, and a pharmacological inhibitor of MEK reversed TGFß's inhibitory effect on myogenesis, as indicated by a myogenin promoter-reporter gene, sarcomeric myosin heavy chain accumulation, and phenotypic myotube formation. Furthermore, we found that c-Jun, a known potent repressor of myogenesis, which is coincidently also a down-stream target of MEK/ERK signaling, was phosphorylated and accumulates in the nucleus in response to TGFß activation. Taken together, these observations support a model in which TGFß activates a MEK/ERK/c-Jun pathway to repress skeletal myogenesis, maintaining the pluripotent undifferentiated state in myogenic progenitors.

Management of Indiana pouch stones through a percutaneous approach: A single center experience.

OBJECTIVE: We present our experience of the treatment of reservoir stones using a percutaneous approach in patients with Indiana pouch urinary diversions. MATERIAL AND METHODS: Patients who were treated percutaneously for Indiana pouch reservoir stones between January 2008 and December 2018 were identified from the hospital database, and their data were retrospectively analyzed. Patient charts were reviewed for stone burden, surgery details, and postoperative complications. The Indiana pouch was punctured under a direct ultrasound guidance, and a 30F sheath was placed into the pouch. A urologist removed the stones by inserting a rigid nephroscope through the sheath. A Foley catheter was left in the pouch through the percutaneous tract and opened to drainage. RESULTS: Seven patients (mean age: 47.3±14.7 years) were included. All patients were stone free after the procedure. The median stone number was 3 (range: 1-8). The mean maximum stone diameter was 24.4±4.9 mm (range: 19-33 mm). Six patients were successfully treated in one session, whereas 1 patient required two treatment sessions. The median postoperative hospital admission was 1 day (range: 1-5 days). The Foley catheters were removed after a median of 18 days (range: 10-19 days). No major complications were reported. CONCLUSION: The percutaneous approach for Indiana pouch reservoir stones treatment ensures direct and safe management without major periprocedural complications.

TNAP limits TGF-ß-dependent cardiac and skeletal muscle fibrosis by inactivating the SMAD2/3 transcription factors.

Fibrosis is associated with almost all forms of chronic cardiac and skeletal muscle diseases. The accumulation of extracellular matrix impairs the contractility of muscle cells contributing to organ failure. Transforming growth factor ß (TGF-ß) plays a pivotal role in fibrosis, activating pro-fibrotic gene programmes via phosphorylation of SMAD2/3 transcription factors. However, the mechanisms that control de-phosphorylation of SMAD2 and SMAD3 (SMAD2/3) have remained poorly characterized. Here, we show that tissue non-specific alkaline phosphatase (TNAP, also known as ALPL) is highly upregulated in hypertrophic hearts and in dystrophic skeletal muscles, and that the abrogation of TGF-ß signalling in TNAP-positive cells reduces vascular and interstitial fibrosis. We show that TNAP colocalizes and interacts with SMAD2. The TNAP inhibitor MLS-0038949 increases SMAD2/3 phosphorylation, while TNAP overexpression reduces SMAD2/3 phosphorylation and the expression of downstream fibrotic genes. Overall our data demonstrate that TNAP negatively regulates TGF-ß signalling and likely represents a mechanism to limit fibrosis.

Smad7:ß-catenin complex regulates myogenic gene transcription.

Recent reports indicate that Smad7 promotes skeletal muscle differentiation and growth. We previously documented a non-canonical role of nuclear Smad7 during myogenesis, independent of its role in TGF-ß signaling. Here further characterization of the myogenic function of Smad7 revealed ß-catenin as a Smad7 interacting protein. Biochemical analysis identified a Smad7 interaction domain (SID) between aa575 and aa683 of ß-catenin. Reporter gene analysis and chromatin immunoprecipitation demonstrated that Smad7 and ß-catenin are cooperatively recruited to the extensively characterized ckm promoter proximal region to facilitate its muscle restricted transcriptional activation in myogenic cells. Depletion of endogenous Smad7 and ß-catenin in muscle cells reduced ckm promoter activity indicating their role during myogenesis. Deletion of the ß-catenin SID substantially reduced the effect of Smad7 on the ckm promoter and exogenous expression of SID abolished ß-catenin function, indicating that SID functions as a trans dominant-negative regulator of ß-catenin activity. ß-catenin interaction with the Mediator kinase complex through its Med12 subunit led us to identify MED13 as an additional Smad7-binding partner. Collectively, these studies document a novel function of a Smad7-MED12/13-ß-catenin complex at the ckm locus, indicating a key role of this complex in the program of myogenic gene expression underlying skeletal muscle development and regeneration.

FMRP recruitment of ß-catenin to the translation pre-initiation complex represses translation.

Canonical Wnt/ß-catenin signaling is an essential regulator of various cellular functions throughout development and adulthood. Aberrant Wnt/ß-catenin signaling also contributes to various pathologies including cancer, necessitating an understanding of cell context-dependent mechanisms regulating this pathway. Since protein-protein interactions underpin ß-catenin function and localization, we sought to identify novel ß-catenin interacting partners by affinity purification coupled with tandem mass spectrometry in vascular smooth muscle cells (VSMCs), where ß-catenin is involved in both physiological and pathological control of cell proliferation. Here, we report novel components of the VSMC ß-catenin interactome. Bioinformatic analysis of the protein networks implies potentially novel functions for ß-catenin, particularly in mRNA translation, and we confirm a direct interaction between ß-catenin and the fragile X mental retardation protein (FMRP). Biochemical studies reveal a basal recruitment of ß-catenin to the messenger ribonucleoprotein and translational pre-initiation complex, fulfilling a translational repressor function. Wnt stimulation antagonizes this function, in part, by sequestering ß-catenin away from the pre-initiation complex. In conclusion, we present evidence that ß-catenin fulfills a previously unrecognized function in translational repression.

TGFß-TAZ/SRF signalling regulates vascular smooth muscle cell differentiation.

Vascular smooth muscle cells (VSMCs) do not terminally differentiate; they modulate their phenotype between proliferative and differentiated states, which is a major factor contributing to vascular diseases. TGFß signalling has been implicated in inducing VSMC differentiation, although the exact mechanism remains largely unknown. Our goal was to assess the network of transcription factors involved in the induction of VSMC differentiation, and to determine the role of TAZ in promoting the quiescent VSMC phenotype. TGFß robustly induces VSMC marker genes in 10T1/2 mouse embryonic fibroblast cells and the potent transcriptional regulator TAZ has been shown to retain Smad complexes on DNA. Thus, the role of TAZ in regulation of VSMC differentiation was studied. Using primary aortic VSMCs coupled with siRNA-mediated gene silencing, our studies reveal that TAZ is required for TGFß induction of smooth muscle genes and is also required for the differentiated VSMC phenotype; synergy between TAZ and SRF, and TAZ and Myocardin (MyoC856), in regulating smooth muscle gene activation was observed. These data provide evidence of components of a novel signalling pathway that links TGFß signalling to induction of smooth muscle genes through a mechanism involving regulation of TAZ and SRF proteins. In addition, we report a physical interaction of TAZ and MyoC856. These observations elucidate a novel level of control of VSMC induction which may have implications for vascular diseases and congenital vascular malformations.

Fermentative production of butanol: Perspectives on synthetic biology.

Apprehensions relating to global warming, climate change, pollution, rising energy demands as well as fluctuating crude oil prices and supply are leading to a shift in global interest to find suitable alternatives to fossil fuels. This review aims to highlight the many different facets of butanol as an advanced next-generation transportation biofuel. Butanol has fuel properties almost on a par with gasoline, such as high energy content, low vapor pressure, non-hygroscopic nature, less volatility, flexible fuel blends and high octane number. The paper reviews some recent advances in acetone-butanol-ethanol fermentation with special emphasis on the primary challenges encountered in butanol fermentation, including butanol toxicity, solvent intolerance and bacteriophage contamination. The mechanisms for butanol recovery techniques have been covered along with their benefits and limitations. A comprehensive discussion of genetic and metabolic engineering of butanol-producing microorganisms is made for the prospective development of industrially-relevant strains that can overcome the technical challenges involved in efficient butanol production.

Regulation of Hspb7 by MEF2 and AP-1: implications for Hspb7 in muscle atrophy.

Mycocyte enhancer factor 2 (MEF2) and activator protein 1 (AP-1) transcription complexes have been individually implicated in myogenesis, but their genetic interaction has not previously been addressed. Using MEF2A, c-Jun and Fra-1 chromatin immunoprecipitation sequencing (ChIP-seq) data and predicted AP-1 consensus motifs, we identified putative common MEF2 and AP-1 target genes, several of which are implicated in regulating the actin cytoskeleton. Because muscle atrophy results in remodelling or degradation of the actin cytoskeleton, we characterized the expression of putative MEF2 and AP-1 target genes (Dstn, Flnc, Hspb7, Lmod3 and Plekhh2) under atrophic conditions using dexamethasone (Dex) treatment in skeletal myoblasts. Heat shock protein b7 (Hspb7) was induced by Dex treatment and further analyses revealed that loss of MEF2A using siRNA prevented Dex-regulated induction of Hspb7. Conversely, ectopic Fra-2 or c-Jun expression reduced Dex-mediated upregulation of Hspb7 whereas AP-1 depletion enhanced Hspb7 expression. In vivo, expression of Hspb7 and other autophagy-related genes was upregulated in response to atrophic conditions in mice. Manipulation of Hspb7 levels in mice also impacted gross muscle mass. Collectively, these data indicate that MEF2 and AP-1 confer antagonistic regulation of Hspb7 gene expression in skeletal muscle, with implications for autophagy and muscle atrophy.

Percutaneous Nephrolithotomy in Patients With BMI >50: Single Surgeon Outcomes and Feasibility.

OBJECTIVE: To evaluate the use of percutaneous nephrolithotomy (PNL) and technical approach in the super obese population (body mass index [BMI] ≥ 50). MATERIALS AND METHODS: We performed a retrospective review of 31 consecutive PNL cases with a BMI > 50 from a single surgeon (SYN) from 1995 to 2013. Procedures were performed in the prone position, and upper pole access was used. Operative time, length of hospital stay, stone burden, complication rates, and stone-free rates were measured. RESULTS: Of the 31 patients who underwent PNL (age 51.2 ± 12; 71% female), the mean BMI was 59.1 ± 6 kg/m(2) (range 50.4-71.7 kg/m(2)). Mean stone burden was 3.8 cm ± 2. The majority of patients (90.3%) had an upper pole puncture site for access with an operative time of 122.1 ± 75 minutes. The technique was similar to non-obese patients; however, there was a need for extra-long instrumentation. The overall stone-free rate was 71%, with utilization of a second-look PNL in 11 cases. The complication rate, Clavien grade 3 or higher, was 9.7% (3 of 31). CONCLUSION: PNL is technically feasible, safe, and effective in patients with a BMI ≥ 50. The complication rate, length of hospital stay, and stone-free rate with use of second-look PNL in super obese patients are comparable to severely obese patients. Intervention should not be automatically ruled out or delayed based on the patient's BMI alone.

A p38 Mitogen-Activated Protein Kinase-Regulated Myocyte Enhancer Factor 2-ß-Catenin Interaction Enhances Canonical Wnt Signaling.

Canonical Wnt/ß-catenin signaling plays a major role in various biological contexts, such as embryonic development, cell proliferation, and cancer progression. Previously, a connection between p38 mitogen-activated protein kinase (MAPK) signaling and Wnt-mediated activation of ß-catenin was implied but poorly understood. In the present study, we investigated potential cross talk between p38 MAPK and Wnt/ß-catenin signaling. Here we show that a loss of p38 MAPK α/ß function reduces ß-catenin nuclear accumulation in Wnt3a-stimulated primary vascular smooth muscle cells (VSMCs). Conversely, active p38 MAPK signaling increases ß-catenin nuclear localization and target gene activity in multiple cell types. Furthermore, the effect of p38 MAPK α/ß on ß-catenin activity is mediated through phosphorylation of a key p38 MAPK target, myocyte enhancer factor 2 (MEF2). Here we report a p38 MAPK-mediated, phosphorylation-dependent interaction between MEF2 and ß-catenin in multiple cell types and primary VSMCs that results in (i) increased ß-catenin nuclear retention, which is reversed by small interfering RNA (siRNA)-mediated MEF2 gene silencing; (ii) increased activation of MEF2 and Wnt/ß-catenin target genes; and (iii) increased Wnt-stimulated cell proliferation. These observations provide mechanistic insight into a fundamental level of cross talk between p38 MAPK/MEF2 signaling and canonical Wnt signaling.

Adiponectin is required for cardiac MEF2 activation during pressure overload induced hypertrophy.

Cardiomyocyte (CM) hypertrophy and increased heart mass in response to pressure overload are associated with hyper-activation of the myocyte enhancer factor-2 (MEF2) family of transcriptional regulators, and concomitant initiation of the fetal gene program. Adiponectin, an adipokine that is reduced in individuals with obesity and diabetes, has been characterized both as a negative regulator or permissive factor in cardiac hypertrophy. We therefore sought to analyze temporal regulation of MEF2 activity in response to pressure overload (PO) and changes in adiponectin status. To address this we crossed a well characterized transgenic MEF2 "sensor" mouse (MEF2-lacZ) with adiponectin null mice (Ad-KO) to create compound MEF2 lacZ/Ad-KO mice. Initially, we established that transverse aortic banding induced PO in wild-type (WT) mice increased heart mass and CM hypertrophy from 1 to 4weeks following surgery, indicated by increased CM diameter and heart weight/tibia length ratio. This was associated with cardiac dysfunction determined by echocardiography. Hypertrophic changes and dysfunction were observed in Ad-KO mice 4weeks following surgery. MEF2 lacZ activity and endogenous ANF mRNA levels, used as indicators of hypertrophic gene activation, were both robustly increased in WT mice after MTAB but attenuated in the Ad-KO background. Furthermore, activation of the pro-hypertrophic molecule p38 was increased following MTAB surgery in WT mice, but not in Ad-KO animals, and treatment of primary isolated CM with recombinant adiponectin induced p38 phosphorylation in a time dependent manner. Adiponectin also increased MEF2 activation in primary cardiomyocytes, an effect attenuated by p38 MAPK inhibition. In conclusion, our data indicate that robust hypertrophic MEF2 activation in the heart in vivo requires a background of adiponectin signaling and that adiponectin signaling in primary isolated CM directly enhances MEF2 activity through activation of p38 MAPK. We conclude that adiponectin is required for full induction of cardiomyocyte MEF2 activation, thus contributing to the myocardial hypertrophic gene expression program in response to PO.