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Mitochondria, which act as sensors of metabolic homeostasis and metabolite signaling, form a dynamic intracellular network that continuously changes shape, size and localization to respond to localized cellular energy demands. Mitochondrial dynamics and function depend on interactions with the F-actin cytoskeleton that are poorly understood. Here, we show that SET domain protein 3 (SETD3), a recently described actin histidine methyltransferase, directly methylates actin at histidine-73 and enhances F-actin polymerization on mitochondria. SETD3 is a mechano-sensitive enzyme that is localized on the outer mitochondrial membrane and promotes actin polymerization around mitochondria. SETD3 loss of function leads to diminished F-actin around mitochondria and a decrease in mitochondrial branch length, branch number and mitochondrial movement. Our functional analysis revealed that SETD3 is required for oxidative phosphorylation, and mitochondrial complex I assembly and function. Our data further indicate that SETD3 regulates F-actin formation around mitochondria and is essential for maintaining mitochondrial morphology, movement and function. Finally, we discovered that SETD3 levels are regulated by extracellular matrix (ECM) stiffness and regulate mitochondrial shape in response to changes in ECM stiffness. These findings provide new insight into the mechanism for F-actin polymerization around mitochondria. [ABSTRACT FROM AUTHOR]

Background: Myeloid cells play critical roles in the regulation of myocardial injury and repair. Clonal hematopoiesis (CH)‐related mutations in genes, such as Ten‐eleven Translocation 2 (TET2), can impair myeloid cells and are associated with increased risk of cardiovascular disease (CVD). How Tet2 loss‐of‐function (LOF) impacts myeloid cells and disrupts normal myocardial repair remains unclear. Methods: We established ischemia‐induced myocardial infarction (MI) in a myeloid‐specific Tet2‐deficient mouse model. The echocardiographic assessment was conducted to evaluate the cardiac function. Histological analysis was performed to evaluate morphological changes in infarcted areas and fibrosis. To monitor the dynamic changes of myeloid cells in cardiac tissues during cardiac remodeling after MI, we performed longitudinal analysis on subsets of myeloid cells using flow cytometry. We performed immunofluorescence (IF) staining to examine the DNA damage and genome instability caused by Tet2 LOF. Gene expression was assessed by real‐time qRT‐PCR. Stimulator of Interferon Genes (STING) pathway activation was assessed using various methods, including Western blotting, flow cytometry, ELISA and IF staining of key signaling proteins involved in this pathway. Additionally, H‐151 was used as a pharmacological tool to antagonize augmented STING activation in the murine MI model. Results: We observed a substantial increase of neutrophils in the post‐MI mice, which contributes to adverse outcomes during heart repair. Mechanistically, Tet2‐deficient myeloid cells exhibited increased genome instability, accompanied with augmented activation of the STING pathway. Furthermore, the use of H‐151 a covalent STING binder that targets the cysteine residue at position 91 and functions as a potent STING antagonist, led to a substantial decrease in neutrophil populations in Tet2‐deficient mice following myocardial infarction, thereby reversing adverse cardiac outcomes. Conclusion: Our novel findings establish the rationale for targeting the cGAS‐STING pathway as a promising therapeutic strategy to mitigate cardiovascular disease risk in individuals with clonal hematopoiesis harboring TET2 loss‐of‐function mutations. Highlights: Myeloid‐specific Tet2 depletion promotes neutrophil expansion upon myocardium infarction (MI);Tet2‐deficient myeloid cells exhibit increased genome instability and cGAS‐STING overactivation;STING antagonist H‐151 treatment reduces neutrophil expansion in Tet2‐deficient mice after MI and mitigates deleterious cardiac outcomes. [ABSTRACT FROM AUTHOR]

Correct cardiac development is essential for fetal and adult life. Disruptions in a variety of signaling pathways result in congenital heart defects, including outflow and inflow tract defects. We previously found that WNT11 regulates outflow tract development. However, tissue specific requirements for WNT11 in this process remain unknown and whether WNT11 is required for inflow tract development has not been addressed. Here we find that germline Wnt11 null mice also show hypoplasia of the dorsal mesenchymal protrusion (DMP), which is required for atrioventricular septation. Ablation of Wnt11 with myocardial cTnTCre recapitulated outflow tract defects observed in germline Wnt11 null mice, but DMP development was unaffected. In contrast, ablation of Wnt11 with Isl1Cre fully recapitulated both outflow tract and DMP defects of Wnt11 germline nulls. DMP hypoplasia in Wnt11 mutants was associated with reduced proliferation within the DMP, but no evident defects in myocardial differentiation of the DMP. Examination of Pitx2-, Axin2-, or Patched-lacZ reporter mice revealed no alterations in reporter expression, suggesting that WNT11 was required downstream of, or in parallel to, these signaling pathways to regulate DMP formation. These studies revealed a previously unappreciated role for WNT11 for DMP formation and distinct tissue-specific requirements for WNT11 in outflow tract and DMP development.

In the adult liver, the Hippo pathway mammalian STE20-like protein kinases 1 and 2 and large tumor suppressor homologs 1 and 2 (LATS1/2) control activation of the transcriptional coactivators Yes-associated protein (YAP) and WW domain containing transcription regulator 1 (TAZ) in hepatocytes and biliary epithelial cells, thereby regulating liver cell proliferation, differentiation, and malignant transformation. Less is known about the contribution of Hippo signaling to liver development. We used conditional mutagenesis to show that the Hippo signaling pathway kinases LATS1 and LATS2 are redundantly required during mouse liver development to repress YAP and TAZ in both the biliary epithelial and hepatocyte lineages. In the absence of LATS1/2, biliary epithelial cells exhibit excess proliferation while hepatoblasts fail to mature into hepatocytes, defects that result in perinatal lethality. Using an in vitro hepatocyte differentiation assay, we demonstrate that YAP activity decreases and Hippo pathway kinase activities increase upon differentiation. In addition, we show that YAP activation in vitro, resulting from either depletion of its negative regulators LATS1/2 or expression of a mutant form of YAP that is less efficiently phosphorylated by LATS1/2, results in transcriptional suppression of genes that normally accompany hepatocyte maturation. Moreover, we provide evidence that YAP activity is repressed by Hippo pathway activation upon hepatocytic maturation in vitro. Finally, we examine the localization of YAP during fetal liver development and show that higher levels of YAP are found in biliary epithelial cells, while in hepatocytes YAP levels decrease with hepatocyte maturation.ConclusionHippo signaling, mediated by the LATS1 and LATS2 kinases, is required to restrict YAP and TAZ activation during both biliary and hepatocyte differentiation. These findings suggest that dynamic regulation of the Hippo signaling pathway plays an important role in differentiation and functional maturation of the liver. (Hepatology 2016;64:1757-1772).