Microenvironment stiffness requires decellularized cardiac extracellular matrix to promote heart regeneration in the neonatal mouse heart.

The transient period of regeneration potential in the postnatal heart suggests molecular changes with maturation influence the cardiac response to damage. We have previously demonstrated that injury and exercise can stimulate cardiomyocyte proliferation in the adult heart suggesting a sensitivity to exogenous signals. Here, we consider whether exogenous fetal ECM and mechanically unloading interstitial matrix can drive regeneration after myocardial infarction (MI) surgery in low-regenerative hearts of day5 mice. Compared to controls, exogenous fetal ECM increases cardiac function and lowers fibrosis at 3 weeks post-injury and this effect can be augmented by softening heart tissue. In vitro experiments support a mechano-sensitivity to exogenous ECM signaling. We tested potential mechanisms and observed that fetal ECM increases nuclear YAP localization which could be enhanced by pharmacological stabilization of the cytoskeleton. Blocking YAP expression lowered fetal ECM effects though not completely. Lastly we observed mechanically unloading heart interstitial matrix increased agrin expression, an extracellular node in the YAP signaling pathway. Collectively, these data support a combined effect of exogenous factors and mechanical activity in altering agrin expression, cytoskeletal remodeling, and YAP signaling in driving cardiomyocyte cell cycle activity and regeneration in postnatal non-regenerative mice. STATEMENT OF SIGNIFICANCE: With the purpose of developing regenerative strategies, we investigate the influence of the local niche on the cardiac injury response. We conclude tissue stiffness, as anticipated in aging or disease, impairs regenerative therapeutics. Most novel, mechanical unloading facilitates enhanced cardiac regeneration only after cells are pushed into a permissive state by fetal biomolecules. Specifically, mechanical unloading appears to increase extracellular agrin expression that amplifies fetal-stimulation of nuclear YAP signaling which correlates with observed increases of cell cycle activity in cardiomyocytes. The results further suggest the cytoskeleton is critical to this interaction between mechanical unloading and independently actived YAP signaling. Using animal models, tissue explants, and cells, this work indicates that local mechanical stimuli can augment proliferating-permissive cardiomyocytes in the natural cardiac niche.

Wang X ，Senapati S ，Akinbote A ，Gnanasambandam B ，Park PS ，Senyo SE ... -  《-》

Microenvironment Stiffness Amplifies Post-ischemia Heart Regeneration in Response to Exogenous Extracellular Matrix Proteins in Neonatal Mice.

The cardiogenesis of the fetal heart is absent in juveniles and adults. Cross-transplantation of decellularized extracellular matrix (dECM) can stimulate regeneration in myocardial infarct (MI) models. We have previously shown that dECM and tissue stiffness have cooperative regulation of heart regeneration in transiently regenerative day 1 neonatal mice. To investigate underlying mechanisms of mechano-signaling and dECM, we pharmacologically altered heart stiffness and administered dECM hydrogels in non-regenerative mice after MI. The dECM combined with softening exhibits preserved cardiac function, LV geometry, increased cardiomyocyte mitosis and lowered fibrosis while stiffening further aggravated ischemic damage. Transcriptome analysis identified a protein in cardiomyocytes, CLCA2, confirmed to be upregulated after MI and downregulated by dECM in a mechanosensitive manner. Synthetic knock-down of CLCA2 expression induced mitosis in primary rat cardiomyocytes in the dish. Together, our results indicate that therapeutic efficacy of extracellular molecules for heart regeneration can be modulated by heart microenvironment stiffness in vivo.

Wang X ，Pierre V ，Senapati S ，Park PS ，Senyo SE ... -  《-》

Tudor-SN promotes cardiomyocyte proliferation and neonatal heart regeneration through regulating the phosphorylation of YAP.

The neonatal mammalian heart exhibits considerable regenerative potential following injury through cardiomyocyte proliferation, whereas mature cardiomyocytes withdraw from the cell cycle and lose regenerative capacities. Therefore, investigating the mechanisms underlying neonatal cardiomyocyte proliferation and regeneration is crucial for unlocking the regenerative potential of adult mammalian heart to repair damage and restore contractile function following myocardial injury. The Tudor staphylococcal nuclease (Tudor-SN) transgenic (TG) or cardiomyocyte-specific knockout mice (Myh6-Tudor-SN -/-) were generated to investigate the role of Tudor-SN in cardiomyocyte proliferation and heart regeneration following apical resection (AR) surgery. Primary cardiomyocytes isolated from neonatal mice were used to assess the influence of Tudor-SN on cardiomyocyte proliferation in vitro. Affinity purification and mass spectrometry were employed to elucidate the underlying mechanism. H9c2 cells and mouse myocardia with either overexpression or knockout of Tudor-SN were utilized to assess its impact on the phosphorylation of Yes-associated protein (YAP), both in vitro and in vivo. We previously identified Tudor-SN as a cell cycle regulator that is highly expressed in neonatal mice myocardia but downregulated in adults. Our present study demonstrates that sustained expression of Tudor-SN promotes and prolongs the proliferation of neonatal cardiomyocytes, improves cardiac function, and enhances the ability to repair the left ventricular apex resection in neonatal mice. Consistently, cardiomyocyte-specific knockout of Tudor-SN impairs cardiac function and retards recovery after injury. Tudor-SN associates with YAP, which plays important roles in heart development and regeneration, inhibiting phosphorylation at Ser 127 and Ser 397 residues by preventing the association between Large Tumor Suppressor 1 (LATS1) and YAP, correspondingly maintaining stability and promoting nuclear translocation of YAP to enhance the proliferation-related genes transcription. Tudor-SN regulates the phosphorylation of YAP, consequently enhancing and prolonging neonatal cardiomyocyte proliferation under physiological conditions and promoting neonatal heart regeneration after injury.

Su C ，Ma J ，Yao X ，Hao W ，Gan S ，Gao Y ，He J ，Ren Y ，Gao X ，Zhu Y ，Yang J ，Wei M ... -  《Cell Communication and Signaling》

The extracellular matrix protein agrin promotes heart regeneration in mice.

Bassat E ，Mutlak YE ，Genzelinakh A ，Shadrin IY ，Baruch Umansky K ，Yifa O ，Kain D ，Rajchman D ，Leach J ，Riabov Bassat D ，Udi Y ，Sarig R ，Sagi I ，Martin JF ，Bursac N ，Cohen S ，Tzahor E ... -  《-》

Decellularized neonatal cardiac extracellular matrix prevents widespread ventricular remodeling in adult mammals after myocardial infarction.

Heart disease remains a leading killer in western society and irreversibly impacts the lives of millions of patients annually. While adult mammals do not possess the ability to regenerate functional cardiac tissue, neonatal mammals are capable of robust cardiomyocyte proliferation and regeneration within a week of birth. Given this change in regenerative function through development, the extracellular matrix (ECM) from adult tissues may not be conducive to promoting cardiac regeneration, although conventional ECM therapies rely exclusively on adult-derived tissues. Therefore the potential of ECM derived from neonatal mouse hearts (nmECM) to prevent adverse ventricular remodeling in adults was investigated using an in vivo model of acute myocardial infarction (MI). Following a single administration of nmECM, we observed a significant improvement in heart function while adult heart-derived ECM (amECM) did not improve these parameters. Treatment with nmECM limits scar expansion in the left ventricle and promotes revascularization of the injured region. Furthermore, nmECM induced expression of the ErbB2 receptor, simulating a neonatal-like environment and promoting neuregulin-1 associated cardiac function. Inhibition of the ErbB2 receptor effectively prevents these actions, suggesting its role in the context of nmECM as a therapy. This study shows the potential of a neonatal-derived biological material in vivo, diverting from the conventional use of adult-derived ECM therapies in research and the clinic. STATEMENT OF SIGNIFICANCE: The of use extracellular matrix biomaterials to aid tissue repair has been previously reported in many forms of injury. The majority of ECM studies to date utilized ECM derived from adult tissues that are not able to fully regenerate functional tissue. In contrast, this study tests the ability of ECM derived from a regenerative organ, the neonatal heart, to stimulate functional cardiac repair after MI. This study is the first to test its potential in vivo. Our results indicate that extracellular factors present in the neonatal environment can be used to alter the healing response in adults, and we have identified the role of ErbB2 in neonatal ECM-based cardiac repair.

Wang Z ，Long DW ，Huang Y ，Chen WCW ，Kim K ，Wang Y ... -  《-》