A Conductive and Adhesive Hydrogel Composed of MXene Nanoflakes as a Paintable Cardiac Patch for Infarcted Heart Repair.

Myocardial infarction (MI) is a major cause of death worldwide. After the occurrence of MI, the heart frequently undergoes serious pathological remodeling, leading to excessive dilation, electrical disconnection between cardiac cells, and fatal functional damage. Hence, extensive efforts have been made to suppress pathological remodeling and promote the repair of the infarcted heart. In this study, we developed a hydrogel cardiac patch that can provide mechanical support, electrical conduction, and tissue adhesiveness to aid in the recovery of an infarcted heart function. Specifically, we developed a conductive and adhesive hydrogel (CAH) by combining the two-dimensional titanium carbide (Ti3C2Tx) MXene with natural biocompatible polymers [i.e., gelatin and dextran aldehyde (dex-ald)]. The CAH was formed within 250 s of mixing the precursor solution and could be painted. The hydrogel containing 3.0 mg/mL MXene, 10% gelatin, and 5% dex-ald exhibited appropriate material characteristics for cardiac patch applications, including a uniform distribution of MXene, a high electrical conductivity (18.3 mS/cm), cardiac tissue-like elasticity (30.4 kPa), strong tissue adhesion (6.8 kPa), and resistance to various mechanical deformations. The CAH was cytocompatible and induced cardiomyocyte (CM) maturation in vitro, as indicated by the upregulation of connexin 43 expression and a faster beating rate. Furthermore, CAH could be painted onto the heart tissue and remained stably adhered to the beating epicardium. In vivo animal studies revealed that CAH cardiac patch treatment significantly improved cardiac function and alleviated the pathological remodeling of an infarcted heart. Thus, we believe that our MXene-based CAH can potentially serve as a promising platform for the effective repair of various electroactive tissues including the heart, muscle, and nerve tissues.

ANGPTL4 stabilizes atherosclerotic plaques and modulates the phenotypic transition of vascular smooth muscle cells through KLF4 downregulation.

Atherosclerosis, the leading cause of death, is a vascular disease of chronic inflammation. We recently showed that angiopoietin-like 4 (ANGPTL4) promotes cardiac repair by suppressing pathological inflammation. Given the fundamental contribution of inflammation to atherosclerosis, we assessed the role of ANGPTL4 in the development of atherosclerosis and determined whether ANGPTL4 regulates atherosclerotic plaque stability. We injected ANGPTL4 protein twice a week into atherosclerotic Apoe-/- mice and analyzed the atherosclerotic lesion size, inflammation, and plaque stability. In atherosclerotic mice, ANGPTL4 reduced atherosclerotic plaque size and vascular inflammation. In the atherosclerotic lesions and fibrous caps, the number of α-SMA(+), SM22α(+), and SM-MHC(+) cells was higher, while the number of CD68(+) and Mac2(+) cells was lower in the ANGPTL4 group. Most importantly, the fibrous cap was significantly thicker in the ANGPTL4 group than in the control group. Smooth muscle cells (SMCs) isolated from atherosclerotic aortas showed significantly increased expression of CD68 and Krüppel-like factor 4 (KLF4), a modulator of the vascular SMC phenotype, along with downregulation of α-SMA, and these changes were attenuated by ANGPTL4 treatment. Furthermore, ANGPTL4 reduced TNFα-induced NADPH oxidase 1 (NOX1), a major source of reactive oxygen species, resulting in the attenuation of KLF4-mediated SMC phenotypic changes. We showed that acute myocardial infarction (AMI) patients with higher levels of ANGPTL4 had fewer vascular events than AMI patients with lower levels of ANGPTL4 (p < 0.05). Our results reveal that ANGPTL4 treatment inhibits atherogenesis and suggest that targeting vascular stability and inflammation may serve as a novel therapeutic strategy to prevent and treat atherosclerosis. Even more importantly, ANGPTL4 treatment inhibited the phenotypic changes of SMCs into macrophage-like cells by downregulating NOX1 activation of KLF4, leading to the formation of more stable plaques.

PSME4 Degrades Acetylated YAP1 in the Nucleus of Mesenchymal Stem Cells.

Intensive research has focused on minimizing the infarct area and stimulating endogenous regeneration after myocardial infarction. Our group previously elucidated that apicidin, a histone deacetylase (HDAC) inhibitor, robustly accelerates the cardiac commitment of naïve mesenchymal stem cells (MSCs) through acute loss of YAP1. Here, we propose the novel regulation of YAP1 in MSCs. We found that acute loss of YAP1 after apicidin treatment resulted in the mixed effects of transcriptional arrest and proteasomal degradation. Subcellular fractionation revealed that YAP1 was primarily localized in the cytoplasm. YAP1 was acutely relocalized into the nucleus and underwent proteasomal degradation. Interestingly, phosphor-S127 YAP1 was shuttled into the nucleus, suggesting that a mechanism other than phosphorylation governed the subcellular localization of YAP1. Apicidin successfully induced acetylation and subsequent dissociation of YAP1 from 14-3-3, an essential molecule for cytoplasmic restriction. HDAC6 regulated both acetylation and subcellular localization of YAP1. An acetylation-dead mutant of YAP1 retarded nuclear redistribution upon apicidin treatment. We failed to acquire convincing evidence for polyubiquitination-dependent degradation of YAP1, suggesting that a polyubiquitination-independent regulator determined YAP1 fate. Nuclear PSME4, a subunit of the 26 S proteasome, recognized and degraded acetyl YAP1 in the nucleus. MSCs from PSME4-null mice were injected into infarcted heart, and aberrant sudden death was observed. Injection of immortalized human MSCs after knocking down PSME4 failed to improve either cardiac function or the fibrotic scar area. Our data suggest that acetylation-dependent proteasome subunit PSME4 clears acetyl-YAP1 in response to apicidin treatment in the nucleus of MSCs.

The adipokine Retnla deficiency increases responsiveness to cardiac repair through adiponectin-rich bone marrow cells.

Resistin-like alpha (Retnla) is a member of the resistin family and known to modulate fibrosis and inflammation. Here, we investigated the role of Retnla in the cardiac injury model. Myocardial infarction (MI) was induced in wild type (WT), Retnla knockout (KO), and Retnla transgenic (TG) mice. Cardiac function was assessed by echocardiography and was significantly preserved in the KO mice, while worsened in the TG group. Angiogenesis was substantially increased in the KO mice, and cardiomyocyte apoptosis was markedly suppressed in the KO mice. By Retnla treatment, the expression of p21 and the ratio of Bax to Bcl2 were increased in cardiomyocytes, while decreased in cardiac fibroblasts. Interestingly, the numbers of cardiac macrophages and unsorted bone marrow cells (UBCs) were higher in the KO mice than in the WT mice. Besides, phosphorylated histone H3(+) cells were more frequent in bone marrow of KO mice. Moreover, adiponectin in UBCs was notably higher in the KO mice compared with WT mice. In an adoptive transfer study, UBCs were isolated from KO mice to transplant to the WT infarcted heart. Cardiac function was better in the KO-UBCs transplanted group in the WT-UBCs transplanted group. Taken together, proliferative and adiponectin-rich bone marrow niche was associated with substantial cardiac recovery by suppression of cardiac apoptosis and proliferation of cardiac fibroblast.

The Small Protein CydX Is Required for Cytochrome bd Quinol Oxidase Stability and Function in Salmonella enterica Serovar Typhimurium: a Phenotypic Study.

Cytochrome bd quinol oxidases, which have a greater affinity for oxygen than heme-copper cytochrome oxidases (HCOs), promote bacterial respiration and fitness in low-oxygen environments, such as host tissues. Here, we show that, in addition to the CydA and CydB subunits, the small protein CydX is required for the assembly and function of the cytochrome bd complex in the enteric pathogen Salmonella enterica serovar Typhimurium. Mutant S Typhimurium lacking CydX showed a loss of proper heme arrangement and impaired oxidase activity comparable to that of a ΔcydABX mutant lacking all cytochrome bd subunits. Moreover, both the ΔcydX mutant and the ΔcydABX mutant showed increased sensitivity to ß-mercaptoethanol and nitric oxide (NO). Cytochrome bd-mediated protection from ß-mercaptoethanol was not a result of resistance to reducing damage but, rather, was due to cytochrome bd oxidase managing Salmonella respiration, while ß-mercaptoethanol interacted with the copper ions necessary for the HCO activity of the cytochrome bo-type quinol oxidase. Interactions between NO and hemes in cytochrome bd and cytochrome bd-dependent respiration during nitrosative stress indicated a direct role for cytochrome bd in mediating Salmonella resistance to NO. Additionally, CydX was required for S Typhimurium proliferation inside macrophages. Mutants deficient in cytochrome bd, however, showed a significant increase in resistance to antibiotics, including aminoglycosides, d-cycloserine, and ampicillin. The essential role of CydX in cytochrome bd assembly and function suggests that targeting this small protein could be a useful antimicrobial strategy, but potential drug tolerance responses should also be considered.IMPORTANCE Cytochrome bd quinol oxidases, which are found only in bacteria, govern the fitness of many facultative anaerobic pathogens by promoting respiration in low-oxygen environments and by conferring resistance to antimicrobial radicals. Thus, cytochrome bd complex assembly and activity are considered potential therapeutic targets. Here we report that the small protein CydX is required for the assembly and function of the cytochrome bd complex in S Typhimurium under stress conditions, including exposure to ß-mercaptoethanol, nitric oxide, or the phagocytic intracellular environment, demonstrating its crucial function for Salmonella fitness. However, cytochrome bd inactivation also leads to increased resistance to some antibiotics, so considerable caution should be taken when developing therapeutic strategies targeting the CydX-dependent cytochrome bd.