Growth hormone-releasing hormone agonists reduce myocardial infarct scar in swine with subacute ischemic cardiomyopathy

Exogenous Growth Hormone Exacerbates Post-Irradiation Atherosclerosis in Susceptible Epicardial Coronary Arteries

Cardiac exposure to ionizing radiation can damage both the microvasculature and coronary arteries, as well as increase the long-term risk of heart disease, myocardial fibrosis, and conduction abnormalities. Therapeutic agents capable of promoting recovery from radiation injury to the heart are limited. Growth hormone is linked to improved cardiac function following injury. Here, we leveraged a cynomolgus macaque model to determine the long-term outcomes of recombinant human growth hormone (rhGH) therapy on the heart following low-dose ionizing radiation. Macaques were exposed to 2 Gy radiation, treated with rhGH for one month, and assessed after 2 years. Overall, plasma lipid profile, cardiac function, and coronary artery disease were similar between rhGH and placebo treated animals. However, a subgroup of rhGH-treated animals exhibited more extensive atherosclerotic plaques in the coronary arteries. Together, these findings indicate that transient human growth hormone therapy subsequent to a single low dose of ionizing radiation involving the heart does not result in long-term changes to plasma cholesterol but may promote exacerbated coronary artery disease in a subset of individuals.

Stimuli-Responsive Delivery Systems for Intervertebral Disc Degeneration

As a major cause of low back pain, intervertebral disc degeneration is an increasingly prevalent chronic disease worldwide that leads to huge annual financial losses. The intervertebral disc consists of the inner nucleus pulposus, outer annulus fibrosus, and sandwiched cartilage endplates. All these factors collectively participate in maintaining the structure and physiological functions of the disc. During the unavoidable degeneration stage, the degenerated discs are surrounded by a harsh microenvironment characterized by acidic, oxidative, inflammatory, and chaotic cytokine expression. Loss of stem cell markers, imbalance of the extracellular matrix, increase in inflammation, sensory hyperinnervation, and vascularization have been considered as the reasons for the progression of intervertebral disc degeneration. The current treatment approaches include conservative therapy and surgery, both of which have drawbacks. Novel stimuli-responsive delivery systems are more promising future therapeutic options than traditional treatments. By combining bioactive agents with specially designed hydrogels, scaffolds, microspheres, and nanoparticles, novel stimuli-responsive delivery systems can realize the targeted and sustained release of drugs, which can both reduce systematic adverse effects and maximize therapeutic efficacy. Trigger factors are categorized into internal (pH, reactive oxygen species, enzymes, etc.) and external stimuli (photo, ultrasound, magnetic, etc.) based on their intrinsic properties. This review systematically summarizes novel stimuli-responsive delivery systems for intervertebral disc degeneration, shedding new light on intervertebral disc therapy.

Efficacy of a growth hormone-releasing hormone agonist in a murine model of cardiometabolic heart failure with preserved ejection fraction

Heart failure (HF) with preserved ejection fraction (HFpEF) represents a major unmet medical need owing to its diverse pathophysiology and lack of effective therapies. Potent synthetic, agonists (MR-356 and MR-409) of growth hormone-releasing hormone (GHRH) improve the phenotype of models of HF with reduced ejection fraction (HFrEF) and in cardiorenal models of HFpEF. Endogenous GHRH exhibits a broad range of regulatory influences in the cardiovascular (CV) system and aging and plays a role in several cardiometabolic conditions including obesity and diabetes. Whether agonists of GHRH can improve the phenotype of cardiometabolic HFpEF remains untested and unknown. Here we tested the hypothesis that MR-356 can mitigate/reverse the cardiometabolic HFpEF phenotype. C57BL6N mice received a high-fat diet (HFD) plus the nitric oxide synthase inhibitor (l-NAME) for 9 wk. After 5 wk of HFD + l-NAME regimen, animals were randomized to receive daily injections of MR-356 or placebo during a 4-wk period. Control animals received no HFD + l-NAME or agonist treatment. Our results showed the unique potential of MR-356 to treat several HFpEF-like features including cardiac hypertrophy, fibrosis, capillary rarefaction, and pulmonary congestion. MR-356 improved cardiac performance by improving diastolic function, global longitudinal strain (GLS), and exercise capacity. Importantly, the increased expression of cardiac pro-brain natriuretic peptide (pro-BNP), inducible nitric oxide synthase (iNOS), and vascular endothelial growth factor-A (VEGF-A) was restored to normal levels suggesting that MR-356 reduced myocardial stress associated with metabolic inflammation in HFpEF. Thus, agonists of GHRH may be an effective therapeutic strategy for the treatment of cardiometabolic HFpEF phenotype.NEW & NOTEWORTHY This randomized study used rigorous hemodynamic tools to test the efficacy of a synthetic GHRH agonist to improve cardiac performance in a cardiometabolic HFpEF. Daily injection of the GHRH agonist, MR-356, reduced the HFpEF-like effects as evidenced by improved diastolic dysfunction, reduced cardiac hypertrophy, fibrosis, and pulmonary congestion. Notably, end-diastolic pressure and end-diastolic pressure-volume relationship were reset to control levels. Moreover, treatment with MR-356 increased exercise capacity and reduced myocardial stress associated with metabolic inflammation in HFpEF.

Neuroendocrine regulation in stroke

The neuroendocrine system, a crosstalk between the central nervous system and endocrine glands, balances and controls hormone secretion and their functions. Neuroendocrine pathways and mechanisms often get dysregulated following stroke, leading to altered hormone secretion and aberrant receptor expression. Dysregulation of the hypothalamus-pituitary-thyroid (HPT) axis and hypothalamus-pituitary-adrenal (HPA) axis often led to severe stroke outcomes. Post-stroke complications such as cognitive impairment, depression, infection etc. are directly or indirectly influenced by the altered neuroendocrine activity that plays a crucial role in stroke vulnerability and susceptibility. Therefore, it is imperative to explore various neurohormonal inter-relationships in regulating stroke, its outcome, and prognosis. Here, we review the biology of different hormones associated with stroke and explore their regulation with a view towards prospective therapeutics.

Synthetic growth hormone-releasing hormone agonist ameliorates the myocardial pathophysiology characteristic of heart failure with preserved ejection fraction

AIMS

To test the hypothesis that the activation of the growth hormone-releasing hormone (GHRH) receptor signalling pathway within the myocardium both prevents and reverses diastolic dysfunction and pathophysiologic features consistent with heart failure with preserved ejection fraction (HFpEF). Impaired myocardial relaxation, fibrosis, and ventricular stiffness, among other multi-organ morbidities, characterize the phenotype underlying the HFpEF syndrome. Despite the rapidly increasing prevalence of HFpEF, few effective therapies have emerged. Synthetic agonists of the GHRH receptors reduce myocardial fibrosis, cardiomyocyte hypertrophy, and improve performance in animal models of ischaemic cardiomyopathy, independently of the growth hormone axis.

METHODS AND RESULTS

CD1 mice received 4- or 8-week continuous infusion of angiotensin-II (Ang-II) to generate a phenotype with several features consistent with HFpEF. Mice were administered either vehicle or a potent synthetic agonist of GHRH, MR-356 for 4-weeks beginning concurrently or 4-weeks following the initiation of Ang-II infusion. Ang-II-treated animals exhibited diastolic dysfunction, ventricular hypertrophy, interstitial fibrosis, and normal ejection fraction. Cardiomyocytes isolated from these animals exhibited incomplete relaxation, depressed contractile responses, altered myofibrillar protein phosphorylation, and disturbed calcium handling mechanisms (ex vivo). MR-356 both prevented and reversed the development of the pathological phenotype in vivo and ex vivo. Activation of the GHRH receptors increased cAMP and cGMP in cardiomyocytes isolated from control animals but only cAMP in cardiac fibroblasts, suggesting that GHRH-A exert differential effects on cardiomyocytes and fibroblasts.

CONCLUSION

These findings indicate that the GHRH receptor signalling pathway(s) represents a new molecular target to counteract dysfunctional cardiomyocyte relaxation by targeting myofilament phosphorylation and fibrosis. Accordingly, activation of GHRH receptors with potent, synthetic GHRH agonists may provide a novel therapeutic approach to management of the myocardial alterations associated with the HFpEF syndrome.

Cardiac regeneration: Options for repairing the injured heart

Cardiac regeneration is one of the grand challenges in repairing injured human hearts. Numerous studies of signaling pathways and metabolism on cardiac development and disease pave the way for endogenous cardiomyocyte regeneration. New drug delivery approaches, high-throughput screening, as well as novel therapeutic compounds combined with gene editing will facilitate the development of potential cell-free therapeutics. In parallel, progress has been made in the field of cell-based therapies. Transplantation of human pluripotent stem cell (hPSC)-derived cardiomyocytes (hPSC-CMs) can partially rescue the myocardial defects caused by cardiomyocyte loss in large animals. In this review, we summarize current cell-based and cell-free regenerative therapies, discuss the importance of cardiomyocyte maturation in cardiac regenerative medicine, and envision new ways of regeneration for the injured heart.

Improvement of cardiac and systemic function in old mice by agonist of growth hormone-releasing hormone

Age-related diseases such as cardiovascular diseases portend disability, increase health expenditures, and cause late-life mortality. Synthetic agonists of growth hormone-releasing hormone (GHRH) exhibit several favorable effects on heart function and remodeling. Here we assessed whether GHRH agonist MR409 can modulate heart function and systemic parameters in old mice. Starting at the age of 15 months, mice were injected subcutaneously with MR409 (10 µg/day, n = 8) or vehicle (n = 7) daily for 6 months. Mice treated with MR409 showed improvements in exercise activity, cardiac function, survival rate, immune function, and hair growth in comparison with the controls. More stem cell colonies were grown out of the bone marrow recovered from the MR409-treated mice. Mitochondrial functions of cardiomyocytes (CMs) from the MR409-treated mice were also significantly improved with more mitochondrial fusion. Fewer β-gal positive cells were observed in endothelial cells after 10 passages with MR409. In Doxorubicin-treated H9C2 cardiomyocytes, cell senescence marker p21 and reactive oxygen species were significantly reduced after cultured with MR409. MR409 also improved cellular ATP production and oxygen consumption rate in Doxorubicin-treated H9C2 cells. Mitochondrial protein OPA1 long isoform was significantly increased after treatment with MR409. The effects of MR409 were mediated by GHRH receptor and protein kinase A (PKA). In short, GHRH agonist MR409 reversed the aging-associated changes with respect of heart function, mobility, hair growth, cellular energy production, and senescence biomarkers. The improvement of heart function may be related to a better mitochondrial functions through GHRH receptor/cAMP/PKA/OPA1 signaling pathway and relieved cardiac inflammation.

Growth hormone-releasing hormone agonists ameliorate chronic kidney disease-induced heart failure with preserved ejection fraction

Therapies for heart failure with preserved ejection fraction (HFpEF) are lacking. Growth hormone-releasing hormone agonists (GHRH-As) have salutary effects in ischemic and nonischemic heart failure animal models. Accordingly, we hypothesized that GHRH-A treatment ameliorates chronic kidney disease (CKD)-induced HFpEF in a large-animal model. Female Yorkshire pigs (n = 16) underwent 5/6 nephrectomy via renal artery embolization and 12 wk later were randomized to receive daily subcutaneous injections of GHRH-A (MR-409; n = 8; 30 µg/kg) or placebo (n = 8) for 4 to 6 wk. Renal and cardiac structure and function were serially assessed postembolization. Animals with 5/6 nephrectomy exhibited CKD (elevated blood urea nitrogen [BUN] and creatinine) and faithfully recapitulated the hemodynamic features of HFpEF. HFpEF was demonstrated at 12 wk by maintenance of ejection fraction associated with increased left ventricular mass, relative wall thickness, end-diastolic pressure (EDP), end-diastolic pressure/end-diastolic volume (EDP/EDV) ratio, and tau, the time constant of isovolumic diastolic relaxation. After 4 to 6 wk of treatment, the GHRH-A group exhibited normalization of EDP (P = 0.03), reduced EDP/EDV ratio (P = 0.018), and a reduction in myocardial pro-brain natriuretic peptide protein abundance. GHRH-A increased cardiomyocyte [Ca²⁺] transient amplitude (P = 0.009). Improvement of the diastolic function was also evidenced by increased abundance of titin isoforms and their ratio (P = 0.0022). GHRH-A exerted a beneficial effect on diastolic function in a CKD large-animal model as demonstrated by improving hemodynamic, structural, and molecular characteristics of HFpEF. These findings have important therapeutic implications for the HFpEF syndrome.

A thermosensitive, reactive oxygen species-responsive, MR409-encapsulated hydrogel ameliorates disc degeneration in rats by inhibiting the secretory autophagy pathway

Lumbar disc degeneration is a common cause of chronic low back pain and an important contributor to various degenerative lumbar spinal disorders. However, currently there is currently no effective therapeutic strategy for treating disc degeneration. The pro-inflammatory cytokine interleukin-1β (IL-1β) mediates disc degeneration by inducing apoptotic death of nucleus pulposus (NP) cells and degradation of the NP extracellular matrix. Here, we confirmed that extracellular secretion of IL-1β via secretory autophagy contributes to disc degeneration, and demonstrate that a thermosensitive reactive oxygen species (ROS)-responsive hydrogel loaded with a synthetic growth hormone-releasing hormone analog (MR409) can protect against needle puncture-induced disc degeneration in rats. Methods: The expression levels of proteins related to secretory autophagy such as tripartite motif-containing 16 (TRIM16) and microtubule-associated protein light chain 3B (LC3B) were examined in human and rat disc tissues by histology and immunofluorescence. The effects of TRIM16 expression level on IL-1β secretion were examined in THP-1 cells transfected with TRIM16 plasmid or siRNA using ELISA, immunofluorescence, and immunoblotting. The in vitro effects of MR409 on IL-1β were examined in THP-1 cells and primary rat NP cells using ELISA, immunofluorescence, immunoblotting, and qRT-PCR. Further, MR409 was subcutaneously administered to aged mice to test its efficacy against disc degeneration using immunofluorescence, X-ray, micro-CT, and histology. To achieve controllable MR409 release for intradiscal use, MR409 was encapsulated in an injectable ROS-responsive thermosensitive hydrogel. Viscosity, rheological properties, release profile, and biocompatibility were evaluated. Thereafter, therapeutic efficacy was assessed in a needle puncture-induced rat model of disc degeneration at 8 and 12 weeks post-operation using X-ray, magnetic resonance (MR) imaging, histological analysis, and immunofluorescence. Results: Secretory autophagy-related proteins TRIM16 and LC3B were robustly upregulated in degenerated discs of both human and rat. Moreover, while upregulation of TRIM16 facilitated, and knockdown of TRIM16 suppressed, secretory autophagy-mediated IL-1β secretion from THP-1 cells under oxidative stress, MR409 inhibited ROS-induced secretory autophagy and IL-1β secretion by THP-1 cells as well as IL-1β-induced pro-inflammatory and pro-catabolic effects in rat NP cells. Daily subcutaneous injection of MR409 inhibited secretory autophagy and ameliorated age-related disc degeneration in mice. The newly developed ROS-responsive MR409-encapsulated hydrogel provided a reliable delivery system for controlled MR409 release, and intradiscal application effectively suppressed secretory autophagy and needle puncture-induced disc degeneration in rats. Conclusion: Secretory autophagy and associated IL-1β secretion contribute to the pathogenesis of disc degeneration, and MR409 can effectively inhibit this pathway. The ROS-responsive thermosensitive hydrogel encapsulated with MR409 is a potentially efficacious treatment for disc degeneration.

Scar Formation with Decreased Cardiac Function Following Ischemia/Reperfusion Injury in 1 Month Old Swine

Studies in mice show a brief neonatal period of cardiac regeneration with minimal scar formation, but less is known about reparative mechanisms in large mammals. A transient cardiac injury approach (ischemia/reperfusion, IR) was used in weaned postnatal day (P)30 pigs to assess regenerative repair in young large mammals at a stage when cardiomyocyte (CM) mitotic activity is still detected. Female and male P30 pigs were subjected to cardiac ischemia (1 h) by occlusion of the left anterior descending artery followed by reperfusion, or to a sham operation. Following IR, myocardial damage occurred, with cardiac ejection fraction significantly decreased 2 h post-ischemia. No improvement or worsening of cardiac function to the 4 week study end-point was observed. Histology demonstrated CM cell cycling, detectable by phospho-histone H3 staining, at 2 months of age in multinucleated CMs in both sham-operated and IR pigs. Inflammation and regional scar formation in the epicardial region proximal to injury were observed 4 weeks post-IR. Thus, pigs subjected to cardiac IR at P30 show myocardial damage with a prolonged decrease in cardiac function, formation of a regional scar, and increased inflammation, but do not regenerate myocardium even in the presence of CM mitotic activity.

Molecular mechanisms of heart regeneration

The adult mammalian heart is incapable of clinically relevant regeneration. The regenerative deficit in adult mammalian heart contrasts with the fetal and neonatal heart, which demonstrate substantial regenerative capacity after injury. This deficiency in adult mammals is attributable to the lack of resident stem cells after birth, combined with an inability of pre-existing cardiomyocytes to complete cytokinesis. Studies of neonatal heart regeneration in mammals suggest that latent regenerative potential can be re-activated. Dissecting the cellular and molecular mechanisms that promote cardiomyocyte proliferation is key to stimulating true regeneration in adult humans. Here, we review recent advances in our understanding of cardiomyocyte proliferation that suggest molecular approaches to heart regeneration.

Actions and Potential Therapeutic Applications of Growth Hormone-Releasing Hormone Agonists

In this article, we briefly review the identification of GHRH, provide an abridged overview of GHRH antagonists, and focus on studies with GHRH agonists. Potent GHRH agonists of JI and MR class were synthesized and evaluated biologically. Besides the induction of the release of pituitary GH, GHRH analogs promote cell proliferation and exert stimulatory effects on various tissues, which express GHRH receptors (GHRH-Rs). A large body of work shows that GHRH agonists, such as MR-409, improve pancreatic β-cell proliferation and metabolic functions and facilitate engraftment of islets after transplantation in rodents. Accordingly, GHRH agonists offer a new therapeutic approach to treating diabetes. Various studies demonstrate that GHRH agonists promote repair of cardiac tissue, producing improvement of ejection fraction and reduction of infarct size in rats, reduction of infarct scar in swine, and attenuation of cardiac hypertrophy in mice, suggesting clinical applications. The presence of GHRH-Rs in ocular tissues and neuroprotective effects of GHRH analogs in experimental diabetic retinopathy indicates their possible therapeutic applications for eye diseases. Other effects of GHRH agonists, include acceleration of wound healing, activation of immune cells, and action on the central nervous system. As GHRH might function as a growth factor, we examined effects of GHRH agonists on tumors. In vitro, GHRH agonists stimulate growth of human cancer cells and upregulate GHRH-Rs. However, in vivo, GHRH agonists inhibit growth of human cancers xenografted into nude mice and downregulate pituitary and tumoral GHRH-Rs. Therapeutic applications of GHRH analogs are discussed. The development of GHRH analogs should lead to their clinical use.

Stimulating Cardiogenesis as a Treatment for Heart Failure

After myocardial injury, cardiomyocyte loss cannot be corrected by using currently available clinical treatments. In recent years, considerable effort has been made to develop cell-based cardiac repair therapies aimed at correcting for this loss. An exciting crop of recent studies reveals that inducing endogenous repair and proliferation of cardiomyocytes may be a viable option for regenerating injured myocardium. Here, we review current heart failure treatments, the state of cardiomyocyte renewal in mammals, and the molecular signals that stimulate cardiomyocyte proliferation. These signals include growth factors, intrinsic signaling pathways, microRNAs, and cell cycle regulators. Animal model cardiac regeneration studies reveal that modulation of exogenous and cell-intrinsic signaling pathways can induce reentry of adult cardiomyocytes into the cell cycle. Using direct myocardial injection, epicardial patch delivery, or systemic administration of growth molecules, these studies show that inducing endogenous cardiomyocytes to self-renew is an exciting and promising therapeutic strategy to treat cardiac injury in humans.

Agonists of growth hormone-releasing hormone (GHRH) inhibit human experimental cancers in vivo by down-regulating receptors for GHRH

The effects of the growth hormone-releasing hormone (GHRH) agonist MR409 on various human cancer cells were investigated. In H446 small cell lung cancer (SCLC) and HCC827 and H460 (non-SCLC) cells, MR409 promoted cell viability, reduced cell apoptosis, and induced the production of cellular cAMP in vitro. Western blot analyses showed that treatment of cancer cells with MR409 up-regulated the expression of cyclins D1 and D2 and cyclin-dependent kinases 4 and 6, down-regulated p27^kip1, and significantly increased the expression of the pituitary-type GHRH receptor (pGHRH-R) and its splice-variant (SV1). Hence, in vitro MR409 exerts agonistic action on lung cancer cells in contrast to GHRH antagonists. However, in vivo, MR409 inhibited growth of lung cancers xenografted into nude mice. MR409 given s.c. at 5 μg/day for 4 to 8 weeks significantly suppressed growth of HCC827, H460, and H446 tumors by 48.2%, 48.7%, and 65.6%, respectively. This inhibition of tumor growth by MR409 was accompanied by the down-regulation of the expression of pGHRH-R and SV1 in the pituitary gland and tumors. Tumor inhibitory effects of MR409 in vivo were also observed in other human cancers, including gastric, pancreatic, urothelial, prostatic, mammary, and colorectal. This inhibition of tumor growth parallel to the down-regulation of GHRH-Rs is similar and comparable to the suppression of sex hormone-dependent cancers after the down-regulation of receptors for luteinizing hormone-releasing hormone (LHRH) by LHRH agonists. Further oncological investigations with GHRH agonists are needed to elucidate the underlying mechanisms.

Regulation of Vascular Calcification by Growth Hormone-Releasing Hormone and Its Agonists

RATIONALE

Vascular calcification (VC) is a marker of the severity of atherosclerotic disease. Hormones play important roles in regulating calcification; estrogen and parathyroid hormones exert opposing effects, the former alleviating VC and the latter exacerbating it. To date no treatment strategies have been developed to regulate clinical VC.

OBJECTIVE

The objective of this study was to investigate the effect of growth hormone-releasing hormone (GHRH) and its agonist (GHRH-A) on the blocking of VC in a mouse model.

METHODS AND RESULTS

Young adult osteoprotegerin-deficient mice were given daily subcutaneous injections of GHRH-A (MR409) for 4 weeks. Significant reductions in calcification of the aortas of MR409-treated mice were paralleled by markedly lower alkaline phosphatase activity and a dramatic reduction in the expression of transcription factors, including the osteogenic marker gene Runx2 and its downstream factors, osteonectin and osteocalcin. The mechanism of action of GHRH-A was dissected in smooth muscle cells isolated from human and mouse aortas. Calcification of smooth muscle cells induced by osteogenic medium was inhibited in the presence of GHRH or MR409, as evidenced by reduced alkaline phosphatase activity and Runx2 expression. Inhibition of calcification by MR409 was partially reversed by MIA602, a GHRH antagonist, or a GHRH receptor-selective small interfering RNA. Treatment with MR409 induced elevated cytosolic cAMP and its target, protein kinase A which in turn blocked nicotinamide adenine dinucleotide phosphate oxidase activity and reduced production of reactive oxygen species, thus blocking the phosphorylation of nuclear factor κB (p65), a key intermediate in the ligand of receptor activator for nuclear factor-κ B-Runx2/alkaline phosphatase osteogenesis program. A protein kinase A-selective small interfering RNA or the chemical inhibitor H89 abolished these beneficial effects of MR409.

CONCLUSIONS

GHRH-A controls osteogenesis in smooth muscle cells by targeting cross talk between protein kinase A and nuclear factor κB (p65) and through the suppression of reactive oxygen species production that induces the Runx2 gene and alkaline phosphatase. Inflammation-mediated osteogenesis is thereby blocked. GHRH-A may represent a new pharmacological strategy to regulate VC.

Growth hormone-releasing hormone attenuates cardiac hypertrophy and improves heart function in pressure overload-induced heart failure

Pathological cardiac hypertrophy, characterized by heart growth in response to pressure or volume overload, such as in the setting of hypertension, is the main risk factor for heart failure (HF). The identification of therapeutic strategies to prevent or reverse cardiac hypertrophy is therefore a priority for curing HF. It is known that growth hormone-releasing hormone (GHRH) displays cardioprotective functions; however, its therapeutic potential in hypertrophy and HF is unknown. Here we show that GHRH reduces cardiomyocyte hypertrophy in vitro through inhibition of hypertrophic pathways. In vivo, the GHRH analog MR-409 attenuates cardiac hypertrophy in mice subjected to transverse aortic constriction and improves cardiac function. These findings suggest therapeutic use of GHRH analogs for treatment of pathological cardiac hypertrophy and HF.

It has been shown that growth hormone-releasing hormone (GHRH) reduces cardiomyocyte (CM) apoptosis, prevents ischemia/reperfusion injury, and improves cardiac function in ischemic rat hearts. However, it is still not known whether GHRH would be beneficial for life-threatening pathological conditions, like cardiac hypertrophy and heart failure (HF). Thus, we tested the myocardial therapeutic potential of GHRH stimulation in vitro and in vivo, using GHRH or its agonistic analog MR-409. We show that in vitro, GHRH(1-44)NH₂ attenuates phenylephrine-induced hypertrophy in H9c2 cardiac cells, adult rat ventricular myocytes, and human induced pluripotent stem cell-derived CMs, decreasing expression of hypertrophic genes and regulating hypertrophic pathways. Underlying mechanisms included blockade of Gq signaling and its downstream components phospholipase Cβ, protein kinase Cε, calcineurin, and phospholamban. The receptor-dependent effects of GHRH also involved activation of Gα_s and cAMP/PKA, and inhibition of increase in exchange protein directly activated by cAMP1 (Epac1). In vivo, MR-409 mitigated cardiac hypertrophy in mice subjected to transverse aortic constriction and improved cardiac function. Moreover, CMs isolated from transverse aortic constriction mice treated with MR-409 showed improved contractility and reversal of sarcolemmal structure. Overall, these results identify GHRH as an antihypertrophic regulator, underlying its therapeutic potential for HF, and suggest possible beneficial use of its analogs for treatment of pathological cardiac hypertrophy.

Growth Hormone-Releasing Hormone and Its Analogues: Significance for MSCs-Mediated Angiogenesis

Mesenchymal stromal cells (MSCs) are promising candidates for regenerative medicine because of their multipotency, immune-privilege, and paracrine properties including the potential to promote angiogenesis. Accumulating evidence suggests that the inherent properties of cytoprotection and tissue repair by native MSCs can be enhanced by various preconditioning stimuli implemented prior to cell transplantation. Growth hormone-releasing hormone (GHRH), a stimulator in extrahypothalamus systems including tumors, has attracted great attentions in recent years because GHRH and its agonists could promote angiogenesis in various tissues. GHRH and its agonists are proangiogenic in responsive tissues including tumors, and GHRH antagonists have been tested as antitumor agents through their ability to suppress angiogenesis and cell growth. GHRH-R is expressed by MSCs and evolving work from our laboratory indicates that treatment of MSCs with GHRH agonists prior to cell transplantation markedly enhanced the angiogenic potential and tissue reparative properties of MSCs through a STAT3 signaling pathway. In this review we summarized the possible effects of GHRH analogues on cell growth and development, as well as on the proangiogenic properties of MSCs. We also discussed the relationship between GHRH analogues and MSC-mediated angiogenesis. The analyses provide new insights into molecular pathways of MSCs-based therapies and their augmentation by GHRH analogues.

Peripheral activities of growth hormone-releasing hormone

Growth hormone (GH)-releasing hormone (GHRH) is produced by the hypothalamus and stimulates GH synthesis and release in the anterior pituitary gland. In addition to its endocrine role, GHRH exerts a wide range of extrapituitary effects which include stimulation of cell proliferation, survival and differentiation, and inhibition of apoptosis. Accordingly, expression of GHRH, as well as the receptor GHRH-R and its splice variants, has been demonstrated in different peripheral tissues and cell types. Among the direct peripheral activities, GHRH regulates pancreatic islet and β-cell survival and function and endometrial cell proliferation, promotes cardioprotection and wound healing, influences the immune and reproductive systems, reduces inflammation, indirectly increases lifespan and adiposity and acts on skeletal muscle cells to inhibit cell death and atrophy. Therefore, it is becoming increasingly clear that GHRH exerts important extrapituitary functions, suggesting potential therapeutic use of the peptide and its analogs in a wide range of medical settings.