Activation of growth hormone releasing hormone (GHRH) receptor stimulates cardiac reverse remodeling after myocardial infarction (MI).

Both cardiac myocytes and cardiac stem cells (CSCs) express the receptor of growth hormone releasing hormone (GHRH), activation of which improves injury responses after myocardial infarction (MI). Here we show that a GHRH-agonist (GHRH-A; JI-38) reverses ventricular remodeling and enhances functional recovery in the setting of chronic MI. This response is mediated entirely by activation of GHRH receptor (GHRHR), as demonstrated by the use of a highly selective GHRH antagonist (MIA-602). One month after MI, animals were randomly assigned to receive: placebo, GHRH-A (JI-38), rat recombinant GH, MIA-602, or a combination of GHRH-A and MIA-602, for a 4-wk period. We assessed cardiac performance and hemodynamics by using echocardiography and micromanometry derived pressure-volume loops. Morphometric measurements were carried out to determine MI size and capillary density, and the expression of GHRHR was assessed by immunofluorescence and quantitative RT-PCR. GHRH-A markedly improved cardiac function as shown by echocardiographic and hemodynamic parameters. MI size was substantially reduced, whereas myocyte and nonmyocyte mitosis was markedly increased by GHRH-A. These effects occurred without increases in circulating levels of growth hormone and insulin-like growth factor I and were, at least partially, nullified by GHRH antagonism, confirming a receptor-mediated mechanism. GHRH-A stimulated CSCs proliferation ex vivo, in a manner offset by MIA-602. Collectively, our findings reveal the importance of the GHRH signaling pathway within the heart. Therapy with GHRH-A although initiated 1 mo after MI substantially improved cardiac performance and reduced infarct size, suggesting a regenerative process. Therefore, activation of GHRHR provides a unique therapeutic approach to reverse remodeling after MI.

Discrete effects of A57G-myosin essential light chain mutation associated with familial hypertrophic cardiomyopathy.

The functional consequences of the familial hypertrophic cardiomyopathy A57G (alanine-to-glycine) mutation in the myosin ventricular essential light chain (ELC) were assessed in vitro and in vivo using previously generated transgenic (Tg) mice expressing A57G-ELC mutant vs. wild-type (WT) of human cardiac ELC and in recombinant A57G- or WT-protein-exchanged porcine cardiac muscle strips. Compared with the Tg-WT, there was a significant increase in the Ca²âº sensitivity of force (ΔpCa50 ≅ 0.1) and an ~1.3-fold decrease in maximal force per cross section of muscle observed in the mutant preparations. In addition, a significant increase in passive tension in response to stretch was monitored in Tg-A57G vs. Tg-WT strips indicating a mutation-induced myocardial stiffness. Consistently, the hearts of Tg-A57G mice demonstrated a high level of fibrosis and hypertrophy manifested by increased heart weight-to-body weight ratios and a decreased number of nuclei indicating an increase in the two-dimensional size of Tg-A57G vs. Tg-WT myocytes. Echocardiography examination showed a phenotype of eccentric hypertrophy in Tg-A57G mice, enhanced left ventricular (LV) cavity dimension without changes in LV posterior/anterior wall thickness. Invasive hemodynamics data revealed significantly increased end-systolic elastance, defined by the slope of the pressure-volume relationship, indicating a mutation-induced increase in cardiac contractility. Our results suggest that the A57G allele causes disease by means of a discrete modulation of myofilament function, increased Ca²âº sensitivity, and decreased maximal tension followed by compensatory hypertrophy and enhanced contractility. These and other contributing factors such as increased myocardial stiffness and fibrosis most likely activate cardiomyopathic signaling pathways leading to pathologic cardiac remodeling.

S-Nitrosoglutathione Reductase Deficiency Enhances the Proliferative Expansion of Adult Heart Progenitors and Myocytes Post Myocardial Infarction.

BACKGROUND: Mammalian heart regenerative activity is lost before adulthood but increases after cardiac injury. Cardiac repair mechanisms, which involve both endogenous cardiac stem cells (CSCs) and cardiomyocyte cell-cycle reentry, are inadequate to achieve full recovery after myocardial infarction (MI). Mice deficient in S-nitrosoglutathione reductase (GSNOR(-/-)), an enzyme regulating S-nitrosothiol turnover, have preserved cardiac function after MI. Here, we tested the hypothesis that GSNOR activity modulates cardiac cell proliferation in the post-MI adult heart. METHODS AND RESULTS: GSNOR(-/-) and C57Bl6/J (wild-type [WT]) mice were subjected to sham operation (n=3 GSNOR(-/-); n=3 WT) or MI (n=41 GSNOR(-/-); n=65 WT). Compared with WT, GSNOR(-/-) mice exhibited improved survival, cardiac performance, and architecture after MI, as demonstrated by higher ejection fraction (P<0.05), lower endocardial volumes (P<0.001), and diminished scar size (P<0.05). In addition, cardiomyocytes from post-MI GSNOR(-/-) hearts exhibited faster calcium decay and sarcomeric relaxation times (P<0.001). Immunophenotypic analysis illustrated that post-MI GSNOR(-/-) hearts demonstrated enhanced neovascularization (P<0.001), c-kit(+) CSC abundance (P=0.013), and a ≈3-fold increase in proliferation of adult cardiomyocytes and c-kit(+)/CD45(-) CSCs (P<0.0001 and P=0.023, respectively) as measured by using 5-bromodeoxyuridine. CONCLUSIONS: Loss of GSNOR confers enhanced post-MI cardiac regenerative activity, characterized by enhanced turnover of cardiomyocytes and CSCs. Endogenous denitrosylases exert an inhibitory effect over cardiac repair mechanisms and therefore represents a potential novel therapeutic target.

S-nitrosoglutathione reductase-dependent PPARγ denitrosylation participates in MSC-derived adipogenesis and osteogenesis.

Bone marrow-derived mesenchymal stem cells (MSCs) are a common precursor of both adipocytes and osteoblasts. While it is appreciated that PPARγ regulates the balance between adipogenesis and osteogenesis, the roles of additional regulators of this process remain controversial. Here, we show that MSCs isolated from mice lacking S-nitrosoglutathione reductase, a denitrosylase that regulates protein S-nitrosylation, exhibited decreased adipogenesis and increased osteoblastogenesis compared with WT MSCs. Consistent with this cellular phenotype, S-nitrosoglutathione reductase-deficient mice were smaller, with reduced fat mass and increased bone formation that was accompanied by elevated bone resorption. WT and S-nitrosoglutathione reductase-deficient MSCs exhibited equivalent PPARγ expression; however, S-nitrosylation of PPARγ was elevated in S-nitrosoglutathione reductase-deficient MSCs, diminishing binding to its downstream target fatty acid-binding protein 4 (FABP4). We further identified Cys 139 of PPARγ as an S-nitrosylation site and demonstrated that S-nitrosylation of PPARγ inhibits its transcriptional activity, suggesting a feedback regulation of PPARγ transcriptional activity by NO-mediated S-nitrosylation. Together, these results reveal that S-nitrosoglutathione reductase-dependent modification of PPARγ alters the balance between adipocyte and osteoblast differentiation and provides checkpoint regulation of the lineage bifurcation of these 2 lineages. Moreover, these findings provide pathophysiological and therapeutic insights regarding MSC participation in adipogenesis and osteogenesis.

Neutrophils from acute pancreatitis patients cause more severe in vitro endothelial damage compared with neutrophils from healthy donors and are differently regulated by endothelins.

OBJECTIVE: There is evidence that endothelin (ET) 1 affect neutrophil functions and that patients with severe acute pancreatitis have increased plasma levels of ETs. Under appropriate conditions, neutrophils are able to injure the endothelium. In the present study, we compared healthy donors with acute pancreatitis patients for neutrophil degranulation and its ability to injure the endothelium and the contribution of ET-1 to this injury. METHODS: Injury was evaluated by measuring the detachment of endothelial cells (ECV-304) growing in monolayer in coculture with human neutrophils for 4 hours. Neutrophil degranulation was assessed by myeloperoxidase (MPO) activity in coculture supernatants. In some experiments, neutrophils were pretreated with the antagonist of ET(A) receptor (BQ-123, 10(-6) M), which has high affinity for ET-1. RESULTS: Neutrophils from both healthy donors and acute pancreatitis patients caused detachment of endothelial cells, and levels of MPO activity were increased in coculture supernatants. Neutrophils from acute pancreatitis patients caused significantly higher levels of detachment and MPO in the supernatants. Pretreatment of neutrophils with BQ-123 inhibited the detachment caused by neutrophils from healthy donors but not by neutrophils from acute pancreatitis patients. CONCLUSIONS: These results show that neutrophils taken from healthy donors damage the endothelium by a mechanism dependent on ETs acting via ET(A) receptor, whereas neutrophils from acute pancreatitis patients cause more severe damage that is not dependent on ETs in the in vitro system used.