Analysis of Smad Phosphatase Activity In Vitro

MORN4 protects cardiomyocytes against ischemic injury via MFN2-mediated mitochondrial dynamics and mitophagy

The imbalance of mitochondrial fission and fusion dynamics causes ischemic cardiomyocyte apoptosis and heart injury by affecting mitophagy. Regulation of mitochondrial dynamics is an important therapeutic strategy for ischemic heart diseases. Considering the important roles of MORN motifs in heart diseases and chloroplast fission, we aimed to investigate the possible role of MORN repeat-containing protein 4 (MORN4) in the progression of myocardial infarction (MI), ischemic cardiomyocyte apoptosis, mitochondrial dynamics, and mitophagy. We found that in the MI mouse, MORN4 knockdown remarkably accelerated cardiac injury and fibrosis with deteriorating cardiac dysfunction. Sphingosylphosphorylcholine (SPC) alleviated ischemic cardiomyocyte apoptosis and heart injury through increased level of MORN4, indicating a vital function of MORN4 in heart with SPC used to clarify the molecular mechanisms underlying the functions of MORN4. Mechanistically, we found that MORN4 directly binds to MFN2 and promotes the phosphorylation of MFN2 S442 through Rho-associated protein kinase 2 (ROCK2), which mediates beneficial mitophagy induced by mitochondrial dynamics, while SPC promoted the binding of MORN4 and MFN2 and the process. Taken together, our data reveal a new perspective role of MORN4 in ischemic heart injury, and report that SPC could regulate myocardial mitochondrial homeostasis by activating the MORN4-MFN2 axis during the ischemic situation, this finding provides novel targets for improving myocardial ischemia tolerance and rescue of acute myocardial infarction.

Metal dependent protein phosphatase PPM family in cardiac health and diseases

Protein phosphorylation and dephosphorylation is central to signal transduction in nearly every aspect of cellular function, including cardiovascular regulation and diseases. While protein kinases are often regarded as the molecular drivers in cellular signaling with high specificity and tight regulation, dephosphorylation mediated by protein phosphatases is also gaining increasing appreciation as an important part of the signal transduction network essential for the robustness, specificity and homeostasis of cell signaling. Metal dependent protein phosphatases (PPM, also known as protein phosphatases type 2C, PP2C) belong to a highly conserved family of protein phosphatases with unique biochemical and molecular features. Accumulating evidence also indicates important and specific functions of individual PPM isoform in signaling and cellular processes, including proliferation, senescence, apoptosis and metabolism. At the physiological level, abnormal PPM expression and activity have been implicated in major human diseases, including cancer, neurological and cardiovascular disorders. Finally, inhibitors for some of the PPM members have been developed as a potential therapeutic strategy for human diseases. In this review, we will focus on the background information about the biochemical and molecular features of major PPM family members, with emphasis on their demonstrated or potential roles in cardiac pathophysiology. The current challenge and potential directions for future investigations will also be highlighted.

BMP2/Smad signaling pathway is involved in the inhibition function of fibroblast growth factor 21 on vascular calcification

Vascular calcification is extremely common and associated with major adverse cardiovascular events. Fibroblast growth factor (FGF) 21 has been identified as a potent metabolic regulator and a protector of the cardiovascular system. In this study, we aimed to investigate the effect of FGF21 on calcification of vascular smooth muscle cell (VSMC) and its mechanism. FGF21 inhibited beta-glycerophosphate (BGP) induced mineralization in VSMCs as determined by calcium concentration and Alizarin Red S. FGF21 suppressed BGP-induced BMP2/Smad signaling pathway components as well as osteoblast differentiation markers. FGF21 and Noggin could synergistically inhibit BGP-induced BMP2/Smad pathway expressions and calcification. Taken together, FGF21 inhibits vascular calcification in vitro by modulating BMP2/Smad signaling pathway.

Inhibition of osteoblast differentiation by aluminum trichloride exposure is associated with inhibition of BMP-2/Smad pathway component expression

Bone morphogenetic protein-2 (BMP-2)/Smad signaling pathway plays an important role in regulating osteoblast (OB) differentiation. OB differentiation is a key process of bone formation. Aluminum (Al) exposure inhibits bone formation and causes Al-induced bone disease. However, the mechanism is not fully understood. To investigate whether BMP-2/Smad signaling pathway is associated with OB differentiation in aluminum trichloride (AlCl₃)-treated OBs, the primary rat OBs were cultured and exposed to 0 (control group, CG), 1/40 IC₅₀ (low-dose group, LG), 1/20 IC₅₀ (mid-dose group, MG), and 1/10 IC₅₀ (high-dose group, HG) of AlCl₃ for 24 h, respectively. We found that the expressions of OB differentiation markers (Runx-2, Osterix and ALP) and BMP-2/Smad signaling pathway components (BMP-2, BMPR-IA, p-BMPR-IA, BMPR-II, p-Smad1/5/8 and p-Smad1/5/8/4) were all decreased in AlCl₃-treated OBs compared with the CG. These results indicated that inhibition of OB differentiation by AlCl₃ was associated with inhibition of BMP-2/Smad pathway component expression. Our findings provide a novel insight into the mechanism of AlCl₃-induced bone disease.