Changes in the Cardiac GHSR1a-Ghrelin System Correlate With Myocardial Dysfunction in Diabetic Cardiomyopathy in Mice

Abstract

Ghrelin and its receptor, the growth hormone secretagogue receptor 1a (GHSR1a), are present in cardiac tissue. Activation of GHSR1a by ghrelin promotes cardiomyocyte contractility and survival, and changes in myocardial GHSR1a and circulating ghrelin track with end-stage heart failure, leading to the hypothesis that GHSR1a is a biomarker for heart failure. We hypothesized that GHSR1a could also be a biomarker for diabetic cardiomyopathy (DCM). We used two models of streptozotocin (STZ)-induced DCM: group 1, adult mice treated with 35 mg/kg STZ for 3 days; and group 2, neonatal mice treated with 70 mg/kg STZ at days 2 and 5 after birth. In group 1, mild fasting hyperglycemia (11 mM) was first detected 8 weeks after the last injection, and in group 2, severe fasting hyperglycemia (20 mM) was first detected 1 to 3 weeks after the last injection. In group 1, left ventricular function was slightly impaired as measured by echocardiography, and Western blot analysis showed a significant decrease in myocardial GHSR1a. In group 2, GHSR1a levels were also decreased as assessed by Cy5-ghrelin(1–19) fluorescence microscopy, and there was a significant negative correlation between GHSR1a levels and glucose tolerance. There were significant positive correlations between GHSR1a and ghrelin and between GHSR1a and sarcoplasmic reticulum Ca2+-ATPase 2a (SERCA2a), a marker for contractility, but not between GHSR1a and B-type natriuretic peptide, a marker for heart failure. We conclude that the subclinical stage of DCM is accompanied by alterations in the myocardial ghrelin-GHSR1a system, suggesting the possibility of a biomarker for DCM.

Dynamics of the Ghrelin/Growth Hormone Secretagogue Receptor System in the Human Heart Before and After Cardiac Transplantation

“…Serial echocardiographic assessment of LV function following cardiac transplant 5 showed LV recovery to an LVEF > 50% in 80% of patients by 1 month PTx. By 6 months PTx, 6 all patients had normal LV function ( Table 2). Although most patients were receiving HF 7 medications, i.e., angiotensin converting enzyme (ACE) inhibitors/beta blockers/diuretics, prior to 8 transplantation, only a small number continued to receive these medications following surgery.…”

“…By 6 months PTx, 6 all patients had normal LV function ( Table 2). Although most patients were receiving HF 7 medications, i.e., angiotensin converting enzyme (ACE) inhibitors/beta blockers/diuretics, prior to 8 transplantation, only a small number continued to receive these medications following surgery.…”

“…previously used the far-red ghrelin analog probe (Ghrelin(1-18, Lys 18 (Cy5)) to quantify GHSR in 1 situ 4 . This analog binds with high specificity to GHSR in mouse cardiac tissue samples 6 . 2 Therefore, we used Ghrelin(1-18, Lys 18 (Cy5) to quantify the expression of GHSR.…”

“…Following 3 incubation with secondary antibodies, this probe was added to tissue sections for 30 min and used 4 for GHSR detection. Sections were washed with PBS, incubated 8 min with DAPI nuclear stain 5 (1:1000), and mounted with ProLong Gold antifade (Life Technologies) to prevent the tissues from 6 photobleaching. Images were captured with a Nikon Eclipse TE2000-S fluorescent microscope.…”

Single Amino Acid Replacement in G‐7039 Leads to a 70‐fold Increase in Binding toward GHS‐R1a

“…Ghrelin actions are mediated via activation of the G protein coupled receptor (GPCR) growth hormone secretagogue receptor type 1a (GHS‐R1a) . It was originally reported that GHS‐R1a was found within the pituitary gland and hypothalamus, but recent work has revealed a more widespread expression in other tissues, including the brain and heart . GHS‐R1a is also reported to be differentially expressed in certain cancer cells.…”