MED12 regulates a transcriptional network of calcium-handling genes in the heart

The Mediator complex regulates gene transcription by linking basal transcriptional machinery with DNA-bound transcription factors. The activity of the Mediator complex is mainly controlled by a kinase submodule that is composed of 4 proteins, including MED12. Although ubiquitously expressed, Mediator subunits can differentially regulate gene expression in a tissue-specific manner. Here, we report that MED12 is required for normal cardiac function, such that mice with conditional cardiac-specific deletion of MED12 display progressive dilated cardiomyopathy. Loss of MED12 perturbs expression of calcium-handling genes in the heart, consequently altering calcium cycling in cardiomyocytes and disrupting cardiac electrical activity. We identified transcription factors that regulate expression of calcium-handling genes that are downregulated in the heart in the absence of MED12, and we found that MED12 localizes to transcription factor consensus sequences within calcium-handling genes. We showed that MED12 interacts with one such transcription factor, MEF2, in cardiomyocytes and that MED12 and MEF2 co-occupy promoters of calcium-handling genes. Furthermore, we demonstrated that MED12 enhances MEF2 transcriptional activity and that overexpression of both increases expression of calcium-handling genes in cardiomyocytes. Our data support a role for MED12 as a coordinator of transcription through MEF2 and other transcription factors. We conclude that MED12 is a regulator of a network of calcium-handling genes, consequently mediating contractility in the mammalian heart

Platelet Endothelial Cell Adhesion Molecule-1 Mediates Endothelial-Cardiomyocyte Communication and Regulates Cardiac Function

BackgroundDilated cardiomyopathy is characterized by impaired contractility of cardiomyocytes, ventricular chamber dilatation, and systolic dysfunction. Although mutations in genes expressed in the cardiomyocyte are the best described causes of reduced contractility, the importance of endothelial‐cardiomyocyte communication for proper cardiac function is increasingly appreciated. In the present study, we investigate the role of the endothelial adhesion molecule platelet endothelial cell adhesion molecule (PECAM‐1) in the regulation of cardiac function.Methods and ResultsUsing cell culture and animal models, we show that PECAM‐1 expressed in endothelial cells (ECs) regulates cardiomyocyte contractility and cardiac function via the neuregulin‐ErbB signaling pathway. Conscious echocardiography revealed left ventricular (LV) chamber dilation and systolic dysfunction in PECAM‐1−/− mice in the absence of histological abnormalities or defects in cardiac capillary density. Despite deficits in global cardiac function, cardiomyocytes isolated from PECAM‐1−/− hearts displayed normal baseline and isoproterenol‐stimulated contractility. Mechanistically, absence of PECAM‐1 resulted in elevated NO/ROS signaling and NRG‐1 release from ECs, which resulted in augmented phosphorylation of its receptor ErbB2. Treatment of cardiomyocytes with conditioned media from PECAM‐1−/− ECs resulted in enhanced ErbB2 activation, which was normalized by pre‐treatment with an NRG‐1 blocking antibody. To determine whether normalization of increased NRG‐1 levels could correct cardiac function, PECAM‐1−/− mice were treated with the NRG‐1 blocking antibody. Echocardiography showed that treatment significantly improved cardiac function of PECAM‐1−/− mice, as revealed by increased ejection fraction and fractional shortening.ConclusionsWe identify a novel role for PECAM‐1 in regulating cardiac function via a paracrine NRG1‐ErbB pathway. These data highlight the importance of tightly regulated cellular communication for proper cardiac function

Adolescent Fat Embolism Syndrome after Closed Tibial Shaft Fracture: Treatment with Emergent External Fixation

Case. An adolescent male developed fat embolism syndrome 24 hours after sustaining a closed right tibial shaft fracture in a football game. The patient was treated with emergent external fixator application due to declining respiratory and mental status and experienced swift recovery after stabilization. He was treated with an intramedullary nail within 1 week of injury. Conclusion. Pediatric fat embolism syndrome is uncommon, and a high index of suspicion is required to facilitate appropriate orthopaedic involvement. External fixation can be performed emergently with minimal fracture manipulation. Rapid provisional fixation appears to have facilitated recovery in this example

Limitation of individual folding resources in the ER leads to outcomes distinct from the unfolded protein response

ER stress leads to upregulation of multiple folding and quality control components, known as the unfolded protein response (UPR). Glucose Regulated Protein 78 (GRP78) (also known as binding immunoglobulin protein, BiP, and HSPA5) and GRP94 are often upregulated coordinately as part of this homeostatic response. Given that endoplasmic reticulum (ER) chaperones have distinct sets of clients, we asked how cells respond to ablation of individual chaperones. The cellular responses to silencing BiP, GRP94, HSP47, PDIA6 and OS-9, were distinct. When BiP was silenced, a widespread UPR was observed, but when GRP94 was either inhibited or depleted by RNA interference (RNAi), the expression of only some genes was induced, notably those encoding BiP and protein disulfide isomerase A6 (PDIA6). Silencing of HSP47 or OS-9 did not lead to any compensatory induction of other genes. The selective response to GRP94 depletion was distinct from a typical ER stress response, both because other UPR target genes were not affected and because the canonical UPR signaling branches were not activated. The response to silencing of GRP94 did not preclude further UPR induction when chemical stress was imposed. Importantly, re-expression of wild-type GRP94 in the silenced cells prevented the upregulation of BiP and PDIA6, whereas re-expression of an ATPase-deficient GRP94 mutant did not, indicating that cells monitor the activity state of GRP94. These findings suggest that cells are able to distinguish among folding resources and generate distinct responses. © 2012

Preoperative Opioid Informed Consent and Prescribing Practices in Children Undergoing Orthopaedic Trauma Surgery.

This study sought to examine prescribing practices for pediatric patients undergoing orthopaedic trauma surgery and assess the effect of state-mandated preoperative informed consent for opioids. A retrospective single-institution cohort study was done between 2016 and 2018 for surgically managed isolated orthopaedic trauma with cohorting based on the presence of preoperative opioid consent. Analyses examined cohort demographic and procedural factors associated with the number of opioid doses prescribed. A total of 1,793 patients met the study criteria. The proportion of patients prescribed opioids (P = 0.0378) and the number of doses (P < 0.001) were lower in consented patients. Differences were greater among those receiving solution (versus tablets). No cohort differences were observed in refill needs. Nonopioid medications prescribing increased. Multivariate analysis identified multiple factors, including preoperative opioid consent (P = 0.013) associated with fewer prescribed opioid doses. After the implementation of preoperative opioid consenting, patients were prescribed fewer opioid doses after pediatric orthopaedic trauma surgery. The increased utilization of nonopioid therapies was also evident. These changes occurred despite a shorter length of hospital stay and without changes in the studied proxies of postoperative pain control. An increased awareness of opioid risks through formal consent discussion may help to facilitate reduced reliance on opioids for children in the postoperative period