Agonists of growth hormone-releasing hormone stimulate self-renewal of cardiac stem cells and promote their survival

Growth hormone-releasing hormone and its analogues in health and disease

Growth hormone-releasing hormone (GHRH) and its ability to stimulate the production and release of growth hormone from the pituitary were discovered more than four decades ago. Since then, this hormone has been studied extensively and research into its functions is still ongoing. GHRH has multifaceted roles beyond the originally identified functions that encompass a variety of direct extrapituitary effects. In this Review, we illustrate the different biological activities of GHRH, covering the effects of GHRH agonists and antagonists in physiological and pathological contexts, along with the underlying mechanisms. GHRH and GHRH analogues have been implicated in cell growth, wound healing, cell death, inflammation, immune functions, mood disorders, feeding behaviour, neuroprotection, diabetes mellitus and obesity, as well as cardiovascular, lung and neurodegenerative diseases and some cancers. The positive effects observed in preclinical models in vitro and in vivo strongly support the potential use of GHRH agonists and antagonists as clinical therapeutics.

Growth hormone-releasing hormone signaling and manifestations within the cardiovascular system

Growth hormone (GH)-releasing hormone (GHRH), a hypothalamic peptide initially characterized for its role in GH regulation, has gained increasing attention due to its GH-independent action on peripheral physiology, including that of the cardiovascular system. While its effects on the peripheral vasculature are still under investigation, GHRH and synthetic agonists have exhibited remarkable receptor-mediated cardioprotective properties in preclinical models. GHRH and its analogs enhance myocardial function by improving contractility, reducing oxidative stress, inflammation, and offsetting pathological remodeling. Studies performed in small and large animal models have demonstrated the efficacy of these compounds in diverse cardiomyopathies, suggesting their potential as promising therapeutic agents. However, the clinical translation of GHRH synthetic analogs still faces challenges related to the route of administration and potential side effects mainly associated with activation of the GH/IGF-I axis. Despite these hurdles, the compelling evidence supporting their role in cardiac repair makes GHRH analogs attractive candidates for clinical testing in the treatment of various cardiac diseases.

The development of growth hormone-releasing hormone analogs: Therapeutic advances in cancer, regenerative medicine, and metabolic disorders

Growth Hormone-Releasing Hormone (GHRH) and its analogs have gained significant attention for their therapeutic potential across various domains, including oncology, regenerative medicine, and metabolic disorders. Originally recognized for its role in regulating growth hormone (GH) secretion, GHRH has since been discovered to exert broader physiological effects beyond the pituitary gland, with GHRH receptors identified in multiple extrahypothalamic tissues, including tumor cells. This review explores the development of both GHRH agonists and antagonists, focusing on their mechanisms of action, therapeutic applications, and future potential. GHRH agonists have shown promise in promoting tissue regeneration, improving cardiac function, and enhancing islet survival in diabetes. Meanwhile, GHRH antagonists, particularly those in the MIA and AVR series, demonstrate potent antitumor activity by inhibiting cancer cell proliferation and downregulating growth factor pathways, while also exhibiting anti-inflammatory properties. Preclinical studies in models of lung, prostate, breast, and gastrointestinal cancers indicate that GHRH analogs could offer a novel therapeutic approach with minimal toxicity. Additionally, GHRH antagonists are being investigated for their potential in treating neurodegenerative diseases and inflammatory conditions. This review highlights the versatility of GHRH analogs as a promising class of therapeutic agents, poised to impact multiple fields of medicine.

GHRH and its analogues in central nervous system diseases

Growth hormone-releasing hormone (GHRH) is primarily produced by the hypothalamus and stimulates the release of growth hormone (GH) in the anterior pituitary gland, which subsequently regulates the production of hepatic insulin-like growth factor-1 (IGF-1). GH and IGF-1 have potent effects on promoting cell proliferation, inhibiting cell apoptosis, as well as regulating cell metabolism. In central nerve system (CNS), GHRH/GH/IGF-1 promote brain development and growth, stimulate neuronal proliferation, and regulate neurotransmitter release, thereby participating in the regulation of various CNS physiological activities. In addition to hypothalamus-pituitary gland, GHRH and GHRH receptor (GHRH-R) are also expressed in other brain cells or tissues, such as endogenous neural stem cells (NSCs) and tumor cells. Alternations in GHRH/GH/IGF-1 axis are associated with various CNS diseases, for example, Alzheimer's disease, amyotrophic lateral sclerosis and emotional disorders manifest GHRH, GH or IGF-1 deficiency, and GH or IGF-1 supplementation exerts beneficial therapeutic effects on these diseases. CNS tumors, such as glioma, can express GHRH and GHRH-R, and activating this signaling pathway promotes tumor cell growth. The synthesized GHRH antagonists have shown to inhibit glioma cell growth and may hold promising as an adjuvant therapy for treating glioma. In addition, we have shown that GHRH agonist MR-409 can improve neurological sequelae after ischemic stroke by activating extrapituitary GHRH-R signaling and promoting endogenous NSCs-derived neuronal regeneration. This article reviews the involvement of GHRH/GH/IGF-1 in CNS diseases, and potential roles of GHRH agonists and antagonists in treating CNS diseases.

Characterization of Somatotrope Cell Expansion in Response to GHRH in the Neonatal Mouse Pituitary

In humans and mice, loss-of-function mutations in growth hormone-releasing hormone receptor (GHRHR) cause isolated GH deficiency. The mutant GHRHR mouse model, GhrhrLit/Lit (LIT), exhibits loss of serum GH, but also fewer somatotropes. However, how loss of GHRH signaling affects expansion of stem and progenitor cells giving rise to GH-producing cells is unknown. LIT mice and wild-type littermates were examined for differences in proliferation and gene expression of pituitary lineage markers by quantitative reverse transcription polymerase chain reaction and immunohistochemistry at postnatal day 5 (p5) and 5 weeks. At p5, the LIT mouse shows a global decrease in pituitary proliferation measured by proliferation marker Ki67 and phospho-histone H3. This proliferative defect is seen in a pituitary cell expressing POU1F1 with or without GH. SOX9-positive progenitors show no changes in proliferation in p5 LIT mice. Additionally, the other POU1F1 lineage cells are not decreased in number; rather, we observe an increase in lactotrope cell population as well as messenger RNA for Tshb and Prl. In the 5-week LIT pituitary, the proliferative deficit in POU1F1-expressing cells observed neonatally persists, while the number and proliferative proportion of SOX9 cells do not appear changed. Treatment of cultured pituitary explants with GHRH promotes proliferation of POU1F1-expressing cells, but not GH-positive cells, in a mitogen-activated protein kinase-dependent manner. These findings indicate that hypothalamic GHRH targets proliferation of a POU1F1-positive cell, targeted to the somatotrope lineage, to fine tune their numbers.

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.

Growth hormone-releasing hormone receptor signaling in experimental ocular inflammation and neuroprotection

Both inflammation and anti-inflammation are involved in the protection of retinal cells. Antagonists of the hypothalamic growth hormone-releasing hormone receptor (GHRHR) have been shown to possess potent anti-inflammatory properties in experimental disease models of various organs, some with systemic complications. Such effects are also found in ocular inflammatory and neurologic injury studies. In experimental models of mice and rats, both growth hormone-releasing hormone receptor agonists and antagonists may alleviate death of ocular neural cells under certain experimental conditions. This review explores the properties of growth hormone-releasing hormone receptor agonists and antagonists that lead to its protection against inflammatory responses induced by extrinsic agents or neurologic injures in ocular animal models.

Agonistic analog of growth hormone-releasing hormone promotes neurofunctional recovery and neural regeneration in ischemic stroke

Ischemic stroke can induce neurogenesis. However, most stroke-generated newborn neurons cannot survive. It has been shown that MR-409, a potent synthetic agonistic analog of growth hormone-releasing hormone (GHRH), can protect against some life-threatening pathological conditions by promoting cell proliferation and survival. The present study shows that long-term treatment with MR-409 (5 or 10 μg/mouse/d) by subcutaneous (s.c.) injection significantly reduces the mortality, ischemic insult, and hippocampal atrophy, and improves neurological functional recovery in mice operated on for transient middle cerebral artery occlusion (tMCAO). Besides, MR-409 can stimulate endogenous neurogenesis and improve the tMCAO-induced loss of neuroplasticity. MR-409 also enhances the proliferation and inhibits apoptosis of neural stem cells treated with oxygen and glucose deprivation-reperfusion. The neuroprotective effects of MR-409 are closely related to the activation of AKT/CREB and BDNF/TrkB pathways. In conclusion, the present study demonstrates that GHRH agonist MR-409 has remarkable neuroprotective effects through enhancing endogenous neurogenesis in cerebral ischemic mice.

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.

Up-regulation of sex-determining region Y-box 9 (SOX9) in growth hormone-secreting pituitary adenomas

BACKGROUND

Pituitary adenomas are benign brain tumors that cause considerable morbidity and neurological symptoms. SOX9 as a regulatory transcriptional mediator affects normal and tumor cell growth with an undefined role in pituitary adenomas pathogenesis. Thus, in the present study, the expression pattern of SOX9 in GH-secreting pituitary tumors and normal pituitary tissues is investigated.

METHODS

The SOX9 gene expression level was evaluated in 60 pituitary tissues including different types of GH-secreting adenomas and normal pituitary tissues through Real-Time PCR. The protein level of SOX9 was assessed using immunohistochemistry. The correlations of SOX9 gene and protein expression level with the patient's clinical and pathological features were considered.

RESULTS

The SOX9 over-expression was detected in GH-secreting adenomas tumor tissues compared to normal pituitary tissues which were accompanied by overexpression of SOX9 protein in tumor tissues. The over-expression of SOX9 had a significant impact on GH-secreting adenomas tumor incidence with the odds ratio of 8.4 and the diagnostic value of SOX9 was considerable. The higher level of SOX9 expression was associated with invasive and macro tumors in GH-secreting pituitary adenoma patients. The positive correlation of SOX9 gene and protein level was observed and the tumor size and tumor invasive features were valuable in predicting SOX9 expression level in GH-producing pituitary tumors.

CONCLUSION

The study provided the first shreds of evidence regarding the expression pattern of SOX9 in the GH- secreting pituitary adenomas at both gene and protein levels which may emphasize the possible involvement of SOX9 as a mediator in pituitary adenoma tumor formation also open up new intrinsic molecular mechanism regarding pituitary adenoma pathogenesis.

Effect of growth hormone treatment on circulating levels of NT-proBNP in patients with ischemic heart failure

AIMS

Growth hormone (GH) therapy in heart failure (HF) is controversial. We investigated the cardiovascular effects of GH in patients with chronic HF due to ischemic heart disease.

METHODS

In a double-blind, placebo-controlled trial, we randomly assigned 37 patients (mean age 66 years; 95% male) with ischemic HF (ejection fraction [EF] < 40%) to a 9-month treatment with either recombinant human GH (1.4 mg every other day) or placebo, with subsequent 3-month treatment-free follow-up. The primary outcome was change in left ventricular (LV) end-systolic volume measured by cardiac magnetic resonance (CMR). Secondary outcomes comprised changes in cardiac structure and EF. Prespecified tertiary outcomes included changes in New York Heat Association (NYHA) functional class and quality of life (QoL), as well as levels of insulin-like growth factor-1 (IGF-1) and N-terminal pro-brain natriuretic peptide (NT-proBNP).

RESULTS

No changes in cardiac structure or systolic function were identified in either treatment group; nor did GH treatment affect QoL or functional class. In the GH group, circulating levels of IGF-1 doubled from baseline (+105%; p < 0.001) and NT-proBNP levels halved (-48%; p < 0.001) during the treatment period, with subsequently a partial return of both towards baseline levels. No changes in IGF-1 or NT-proBNP were observed in the placebo group at any time during the study.

CONCLUSION

In patients with chronic ischemic HF, nine months of GH treatment was associated with significant increases in levels of IGF-1 and reductions in levels of NT-proBNP, but did not affect cardiac structure, systolic function or functional capacity.

The effects of growth hormone on therapy resistance in cancer

Pituitary derived and peripherally produced growth hormone (GH) is a crucial mediator of longitudinal growth, organ development, metabolic regulation with tissue specific, sex specific, and age-dependent effects. GH and its cognate receptor (GHR) are expressed in several forms of cancer and have been validated as an anti-cancer target through a large body of in vitro, in vivo and epidemiological analyses. However, the underlying molecular mechanisms of GH action in cancer prognosis and therapeutic response had been sparse until recently. This review assimilates the critical details of GH-GHR mediated therapy resistance across different cancer types, distilling the therapeutic implications based on our current understanding of these effects.

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.

IGF-1 and somatocrinin trigger islet differentiation in human amniotic membrane derived mesenchymal stem cells

AIM

To induce differentiation of human amniotic membrane derived mesenchymal stem cells (hAMMSCs) into insulin producing cells (IPCs) by treating with somatocrinin or growth hormone releasing hormone (GHRH) and Insulin-like growth factor-1 (IGF-1).

MAIN METHOD

In this investigation, we cultivated and characterized hAMMSCs and then treated with IGF-1 and somatocrinin to find out whether this combination gives better yield of insulin producing cells. We showed that hAMMSCs can give rise to IPCs on exposure to serum-free defined media containing specific growth factors and differentiating agents in presence of IGF-1 and somatocrinin.

KEY FINDING

A combination of IGF-1 and somatocrinin lead to differentiation of large number of IPCs from hAMMSCs. These IPCs were found to be positive for dithizone indicating their insulin secretory mechanism. Moreover these cells were also found to be positive for C-peptide. IPCs released insulin in response to glucose challenge. Gene expression analysis exhibited significant up-regulation of pancreatic transcription factor GLUT2 and Insulin.

SIGNIFICANCE

Our data thus demonstrates for the first time that somatocrinin and IGF-1 synergistically enhance the differentiation of hAMMSCs into IPCs.

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.

Structural Motif Descriptors as a Way To Elucidate the Agonistic or Antagonistic Activity of Growth Hormone-Releasing Hormone Peptide Analogues

The synthesis of analogues of hypothalamic neuropeptide growth hormone-releasing hormone (GHRH) is an efficient strategy for designing new therapeutic agents. Several promising synthetic agonist and antagonist analogues of GHRH have been developed based on amino acid mutations of the GHRH (1-29) sequence. Because structural information on the activity of the GHRH agonists or antagonists is limited, there is a need for more effective analytical workflows capable of correlating the peptide sequence with biological activity. In the present work, three GHRH agonists-MR-356, MR-406, and MR-409-and three GHRH antagonists-MIA-602, MIA-606, and MIA-690-were investigated to assess the role of substitutions in the amino acid sequence on structural motifs and receptor binding affinities. The use of high resolution trapped ion mobility spectrometry coupled to mass spectrometry allowed the observation of a large number of peptide-specific mobility bands (or structural motif descriptors) as a function of the amino acid sequence and the starting solution environment. A direct correlation was observed between the amino acid substitutions (i.e., basic residues and d/l-amino acids), the structural motif descriptors, and the biological function (i.e., receptor binding affinities of the GHRH agonists and antagonists). The simplicity, ease, and high throughput of the proposed workflow based on the structural motif descriptors can significantly reduce the cost and time during screening of new synthetic peptide analogues.

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.

Expression of progenitor markers is associated with the functionality of a bioartificial adrenal cortex

Encapsulation of primary bovine adrenocortical cells in alginate is an efficacious model of a bioartificial adrenal cortex. Such a bioartificial adrenal cortex can be used for the restoration of lost adrenal function in vivo as well as for in vitro modeling of the adrenal microenvironment and for investigation of cell–cell interactions in the adrenals. The aim of this work was the optimization of a bioartificial adrenal cortex, that is the generation of a highly productive, self-regenerating, long-term functioning and immune tolerant bioartificial organ. To achieve this, it is necessary that adrenocortical stem and progenitor cells are present in the bioartificial gland, as these undifferentiated cells play important roles in the function of the mature gland. Here, we verified the presence of adrenocortical progenitors in cultures of bovine adrenocortical cells, studied the dynamics of their appearance and growth and determined the optimal time point for cell encapsulation. These procedures increased the functional life span and reduced the immunogenicity of the bioartificial adrenal cortex. This model allows the use of the luteinizing hormone-releasing hormone (LHRH) agonist triptorelin, the neuropeptide bombesin, and retinoic acid to alter cell number and the release of cortisol over long periods of time.

Agonistic analogs of growth hormone releasing hormone (GHRH) promote wound healing by stimulating the proliferation and survival of human dermal fibroblasts through ERK and AKT pathways

Decreased or impaired proliferation capability of dermal fibroblasts interferes with successful wound healing. Several growth factors tested failed to fully restore the growth of fibroblasts, possibly due to their rapid degradation by proteases. It is therefore critical to find new agents which have stimulatory effects on fibroblasts while being highly resistant to degradation. In such a scenario, the activities of two agonistic analogs of growth hormone releasing hormone (GHRH), MR-409 and MR-502, were evaluated for their impact on proliferation and survival of primary human dermal fibroblasts. In vitro, both analogs significantly stimulated cell growth by more than 50%. Under serum-depletion induced stress, fibroblasts treated with MR-409 or MR-502 demonstrated better survival rates than control. These effects can be inhibited by either PD98059 or wortmannin. Signaling through MEK/ERK1/2 and PI3K/AKT in an IGF-1 receptor-independent manner is required. In vivo, MR-409 promoted wound closure. Animals treated topically with MR-409 healed earlier than controls in a dose-dependent manner. Histologic examination revealed better wound contraction and less fibrosis in treated groups. In conclusion, MR-409 is a potent mitogenic and anti-apoptotic factor for primary human dermal fibroblasts. Its beneficial effects on wound healing make it a promising agent for future development.

Hypoxic Stress Decreases c-Myc Protein Stability in Cardiac Progenitor Cells Inducing Quiescence and Compromising Their Proliferative and Vasculogenic Potential

Cardiac progenitor cells (CPCs) have been shown to promote cardiac regeneration and improve heart function. However, evidence suggests that their regenerative capacity may be limited in conditions of severe hypoxia. Elucidating the mechanisms involved in CPC protection against hypoxic stress is essential to maximize their cardioprotective and therapeutic potential. We investigated the effects of hypoxic stress on CPCs and found significant reduction in proliferation and impairment of vasculogenesis, which were associated with induction of quiescence, as indicated by accumulation of cells in the G0-phase of the cell cycle and growth recovery when cells were returned to normoxia. Induction of quiescence was associated with a decrease in the expression of c-Myc through mechanisms involving protein degradation and upregulation of p21. Inhibition of c-Myc mimicked the effects of severe hypoxia on CPC proliferation, also triggering quiescence. Surprisingly, these effects did not involve changes in p21 expression, indicating that other hypoxia-activated factors may induce p21 in CPCs. Our results suggest that hypoxic stress compromises CPC function by inducing quiescence in part through downregulation of c-Myc. In addition, we found that c-Myc is required to preserve CPC growth, suggesting that modulation of pathways downstream of it may re-activate CPC regenerative potential under ischemic conditions.

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.

New therapeutic approach to heart failure due to myocardial infarction based on targeting growth hormone-releasing hormone receptor

Background

We previously showed that growth hormone-releasing hormone (GHRH) agonists are cardioprotective following myocardial infarction (MI). Here, our aim was to evaluate the in vitro and in vivo activities of highly potent new GHRH agonists, and elucidate their mechanisms of action in promoting cardiac repair.

Methods and Results

H9c2 cells were cultured in serum-free medium, mimicking nutritional deprivation. GHRH agonists decreased calcium influx and significantly improved cell survival. Rats with cardiac infarction were treated with GHRH agonists or placebo for four weeks. MI size was reduced by selected GHRH agonists (JI-38, MR-356, MR-409); this accompanied an increased number of cardiac c-kit⁺ cells, cellular mitotic divisions, and vascular density. One week post-MI, MR-409 significantly reduced plasma levels of IL-2, IL-6, IL-10 and TNF-α compared to placebo. Gene expression studies revealed favorable outcomes of MR-409 treatment partially result from inhibitory activity on pro-apoptotic molecules and pro-fibrotic systems, and by elevation of bone morphogenetic proteins.

Conclusions

Treatment with GHRH agonists appears to reduce the inflammatory responses post-MI and may consequently improve mechanisms of healing and cardiac remod eling by regulating pathways involved in fibrosis, apoptosis and cardiac repair. Patients with cardiac dysfunction could benefit from treatment with novel GHRH agonists.

Allostery and Biased Agonism at Class B G Protein-Coupled Receptors

Class B G protein-coupled receptors (GPCRs) respond to paracrine or endocrine peptide hormones involved in control of bone homeostasis, glucose regulation, satiety, and gastro-intestinal function, as well as pain transmission. These receptors are targets for existing drugs that treat osteoporosis, hypercalcaemia, Paget's disease, type II diabetes, and obesity and are being actively pursued as targets for numerous other diseases. Exploitation of class B receptors has been limited by difficulties with small molecule drug discovery and development and an under appreciation of factors governing optimal therapeutic efficacy. Recently, there has been increasing awareness of novel attributes of GPCR function that offer new opportunity for drug development. These include the presence of allosteric binding sites on the receptor that can be exploited as drug binding pockets and the ability of individual drugs to enrich subpopulations of receptor conformations to selectively control signaling, a phenomenon termed biased agonism. In this review, current knowledge of biased signaling and small molecule allostery within class B GPCRs is discussed, highlighting areas that have progressed significantly over the past decade, in addition to those that remain largely unexplored with respect to these phenomena.

Pretreatment of Cardiac Stem Cells With Exosomes Derived From Mesenchymal Stem Cells Enhances Myocardial Repair

Background

Exosomes derived from mesenchymal stem cells (MSCs) were proved to boost cell proliferation and angiogenic potency. We explored whether cardiac stem cells (CSCs) preconditioned with MSC exosomes could survive and function better in a myocardial infarction model.

Methods and Results

DiI‐labeled exosomes were internalized with CSCs. They stimulated proliferation, migration, and angiotube formation of CSCs in a dose‐dependent manner. In a rat myocardial infarction model, MSC exosome–preconditioned CSCs had significantly better survival, enhanced capillary density, reduced cardiac fibrosis, and restored long‐term cardiac function. MicroRNA profiling analysis revealed that a set of microRNAs were significantly changed in CSCs after MSC exosome treatment.

Conclusions

Pretreatment of CSCs with MSC exosomes provided a promising strategy to improve survival and angiogenic potency of CSCs.

Beneficial effects of growth hormone-releasing hormone agonists on rat INS-1 cells and on streptozotocin-induced NOD/SCID mice

Agonists of growth hormone-releasing hormone (GHRH) have been previously reported to promote growth, function, and engraftment of islet cells following transplantation. Here we evaluated recently synthesized GHRH agonists on the proliferation and biological functions of rat pancreatic β-cell line (INS-1) and islets. In vitro treatment of INS-1 cells with GHRH agonists increased cell proliferation, the expression of cellular insulin, insulin-like growth factor-1 (IGF1), and GHRH receptor, and also stimulated insulin secretion in response to glucose challenge. Exposure of INS-1 cells to GHRH agonists, MR-356 and MR-409, induced activation of ERK and AKT pathways. Agonist MR-409 also significantly increased the levels of cellular cAMP and the phosphorylation of cAMP response element binding protein (CREB) in INS-1 cells. Treatment of rat islets with agonist, MR-409 significantly increased cell proliferation, islet size, and the expression of insulin. In vivo daily s.c. administration of 10 μg MR-409 for 3 wk dramatically reduced the severity of streptozotocin (STZ)-induced diabetes in nonobese diabetic severe combined immunodeficiency (NOD/SCID) mice. The maximal therapeutic benefits with respect to the efficiency of engraftment, ability to reach normoglycemia, gain in body weight, response to high glucose challenge, and induction of higher levels of serum insulin and IGF1 were observed when diabetic mice were transplanted with rat islets preconditioned with GHRH agonist, MR-409, and received additional treatment with MR-409 posttransplantation. This study provides an improved approach to the therapeutic use of GHRH agonists in the treatment of diabetes mellitus.

cKit+ cardiac progenitors of neural crest origin

The degree to which cKit-expressing progenitors generate cardiomyocytes in the heart is controversial. Genetic fate-mapping studies suggest minimal contribution; however, whether or not minimal contribution reflects minimal cardiomyogenic capacity is unclear because the embryonic origin and role in cardiogenesis of these progenitors remain elusive. Using high-resolution genetic fate-mapping approaches with cKit(CreERT2/+) and Wnt1::Flpe mouse lines, we show that cKit delineates cardiac neural crest progenitors (CNC(kit)). CNC(kit) possess full cardiomyogenic capacity and contribute to all CNC derivatives, including cardiac conduction system cells. Furthermore, by modeling cardiogenesis in cKit(CreERT2)-induced pluripotent stem cells, we show that, paradoxically, the cardiogenic fate of CNC(kit) is regulated by bone morphogenetic protein antagonism, a signaling pathway activated transiently during establishment of the cardiac crescent, and extinguished from the heart before CNC invasion. Together, these findings elucidate the origin of cKit(+) cardiac progenitors and suggest that a nonpermissive cardiac milieu, rather than minimal cardiomyogenic capacity, controls the degree of CNC(kit) contribution to myocardium.

GH-Releasing Hormone Promotes Survival and Prevents TNF-α-Induced Apoptosis and Atrophy in C2C12 Myotubes

Skeletal muscle atrophy is a consequence of different chronic diseases, including cancer, heart failure, and diabetes, and also occurs in aging and genetic myopathies. It results from an imbalance between anabolic and catabolic processes, and inflammatory cytokines, such as TNF-α, have been found elevated in muscle atrophy and implicated in its pathogenesis. GHRH, in addition to stimulating GH secretion from the pituitary, exerts survival and antiapoptotic effects in different cell types. Moreover, we and others have recently shown that GHRH displays antiapoptotic effects in isolated cardiac myocytes and protects the isolated heart from ischemia/reperfusion injury and myocardial infarction in vivo. On these bases, we investigated the effects of GHRH on survival and apoptosis of TNF-α-treated C2C12 myotubes along with the underlying mechanisms. GHRH increased myotube survival and prevented TNF-α-induced apoptosis through GHRH receptor-mediated mechanisms. These effects involved activation of phosphoinositide 3-kinase/Akt pathway and inactivation of glycogen synthase kinase-3β, whereas mammalian target of rapamycin was unaffected. GHRH also increased the expression of myosin heavy chain and the myogenic transcription factor myogenin, which were both reduced by the cytokine. Furthermore, GHRH inhibited TNF-α-induced expression of nuclear factor-κB, calpain, and muscle ring finger1, which are all involved in muscle protein degradation. In summary, these results indicate that GHRH exerts survival and antiapoptotic effects in skeletal muscle cells through the activation of anabolic pathways and the inhibition of proteolytic routes. Overall, our findings suggest a novel therapeutic role for GHRH in the treatment of muscle atrophy-associated diseases.

Transcoronary infusion of cardiac progenitor cells in hypoplastic left heart syndrome: Three-year follow-up of the Transcoronary Infusion of Cardiac Progenitor Cells in Patients With Single-Ventricle Physiology (TICAP) trial

OBJECTIVES

Our aim was to assess midterm safety and clinical outcomes of intracoronary infusion of cardiosphere-derived cells (CDCs) after staged palliation in patients with hypoplastic left heart syndrome (HLHS).

METHODS

In this prospective, controlled study, 14 consecutive patients with HLHS who were undergoing 2- or 3-stage surgical palliations were assigned to receive intracoronary CDC infusion 1 month after cardiac surgery (n = 7), followed by 7 patients allocated to a control group with standard care alone. The primary end point was to assess procedural feasibility and safety; the secondary end point was to evaluate cardiac function and heart failure status through 36-month follow-up.

RESULTS

No complications, including tumor formation, were reported within 36 months after CDC infusion. Echocardiography showed significantly greater improvement in right ventricular ejection fraction (RVEF) in infants receiving CDCs than in controls at 36 months (+8.0% ± 4.7% vs +2.2% ± 4.3%; P = .03). These cardiac function improvements resulted in reduced brain natriuretic peptide levels (P = .04), lower incidence of unplanned catheter interventions (P = .04), and higher weight-for-age z score (P = .02) at 36 months relative to controls. As independent predictors of treatment responsiveness, absolute changes in RVEF at 36 months were negatively correlated with age, weight-for-age z score, and RVEF at CDC infusion.

CONCLUSIONS

Intracoronary CDC infusion after staged procedure in patients with HLHS is safe and improves RVEF, which persists during 36-month follow-up. This therapeutic strategy may enhance somatic growth and reduce incidence of heart failure.

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

BACKGROUND

Growth hormone-releasing hormone agonists (GHRH-As) stimulate cardiac repair following myocardial infarction (MI) in rats through the activation of the GHRH signaling pathway within the heart. We tested the hypothesis that the administration of GHRH-As prevents ventricular remodeling in a swine subacute MI model.

METHODS AND RESULTS

Twelve female Yorkshire swine (25 to 30 kg) underwent transient occlusion of the left anterior descending coronary artery (MI). Two weeks post MI, swine were randomized to receive injections of either 30 μg/kg GHRH-A (MR-409) (GHRH-A group; n=6) or vehicle (placebo group; n=6). Cardiac magnetic resonance imaging and pressure-volume loops were obtained at multiple time points. Infarct, border, and remote (noninfarcted) zones were assessed for GHRH receptor by immunohistochemistry. Four weeks of GHRH-A treatment resulted in reduced scar mass (GHRH-A: -21.9 ± 6.42%; P=0.02; placebo: 10.9 ± 5.88%; P=0.25; 2-way ANOVA; P=0.003), and scar size (percentage of left ventricular mass) (GHRH-A: -38.38 ± 4.63; P=0.0002; placebo: -14.56 ± 6.92; P=0.16; 2-way ANOVA; P=0.02). This was accompanied by improved diastolic strain. Unlike in rats, this reduced infarct size in swine was not accompanied by improved cardiac function as measured by serial hemodynamic pressure-volume analysis. GHRH receptors were abundant in cardiac tissue, with a greater density in the border zone of the GHRH-A group compared with the placebo group.

CONCLUSIONS

Daily subcutaneous administration of GHRH-A is feasible and safe in a large animal model of subacute ischemic cardiomyopathy. Furthermore, GHRH-A therapy significantly reduced infarct size and improved diastolic strain, suggesting a local activation of the GHRH pathway leading to the reparative process.

Tadalafil, a Phosphodiesterase Inhibitor Protects Stem Cells over Longer Period Against Hypoxia/Reoxygenation Injury Through STAT3/PKG-I Signaling

Pharmacological preconditioning (PC) with tadalafil, a PDE5A inhibitor, enhances protein kinase G-1 (PKG-I) activity, resulting in stem cell survival. Protection by PC had two different phases, early (2 h) and late (24 h). However, the mechanism of protection during these phases remained grossly unknown. Mesenchymal stem cells (MSCs) from adult male Fischer-344 rats were cultured and pretreated with tadalafil (100 μM) for an hour and subjected to 2 h of hypoxia (1% O2), followed by reoxygenation (HR: in vitro model mimicking ischemia/reperfusion). We observed (i) increased MSC survival with reduced cell cytotoxicity as revealed by low lactate dehydrogenase release and trypan blue staining, respectively, in tadalafil-treated cells upon HR; (ii) decrease in TUNEL positivity as well as caspase activity; (iii) an increase in pAkt/Akt, iNOS, eNOS, and pGSK3β/GSK3β during the early protection phase of PC, and this protection seemed to be a spontaneous adaptive response of MSCs against HR and was independent of tadalafil, whereas an increase in Bcl2/Bax was tadalafil dependent; and (iv) during the late phase, we observed phosphorylation of STAT3 at serine727, leading to its entry inside the nucleus and binding onto the promoter of PKG-I by three-fold (P<0.05). In conclusion, an increase in Bcl2/Bax during the early phase and transcriptional upregulation of PKG-I by STAT3 during the late phase were responsible for stem cell protection by tadalafil against ischemic injury.