Growth hormone releasing peptide (ghrelin) is synthesized and secreted by cardiomyocytes.
OBJECTIVE
Ghrelin, the endogenous ligand of growth hormone secretagogue receptor (GHS-R), acts on the pituitary and the hypothalamus to stimulate the release of growth hormone (GH) and promotes appetite and adiposity. It has also been reported to increase myocardial contractility, induce vasodilation, and protect against myocardial-infarction-induced heart failure. Though principally gastric in origin, it is also produced by other tissues. This work investigated whether cardiomyocytes synthesize and secrete ghrelin, and how its production in these cells responds to stress and exogenous apoptotic agents.


METHODS
Ghrelin and its receptor expression was studied by RT-PCR, immunohistochemistry, and competitive binding studies in mouse adult cardiomyocyte cell line HL-1, and primary cultured human cardiomyocytes. Ghrelin accumulation in cardiomyocyte culture medium was measured by radioimmunoassay. Viability and apoptosis assays were carried on by MTT and Hoechst dye vital staining, respectively.


RESULTS
RT-PCR showed that HL-1 cells produce mRNAs for both ghrelin and GHS-R, and that GHS-R1a is expressed in human cardiomyocytes; and competitive binding studies using (125)I-labelled ghrelin showed efficient constitutive expression of GHS-R at the surface of HL-1 cells. Immunohistochemistry confirmed the presence of ghrelin in the cytoplasm of HL-1 cells and of isolated human cardiomyocytes in primary culture. Radioimmunoassay showed that ghrelin was secreted by HL-1 cells and human cardiomyocytes into the culture medium. Ghrelin did not modify the viability of HL-1 cells subjected to 12-h starvation, but did protect against the apoptosis inducer cytosine arabinoside (AraC). Finally, production of ghrelin mRNA in HL-1 cardiomyocytes was reduced by AraC but increased if exposure to AraC was preceded by GH treatment.


CONCLUSIONS
Ghrelin is synthesized and secreted by isolated murine and human cardiomyocytes, probably with paracrine/autocrine effects, and may be involved in protecting these cells from apoptosis.
Iglesias
María J
MJ
Unidad de Investigación del Servicio de Cardiología, Laboratorio de Investigación 1, Planta Baja, Area de Investigación y Docencia, Hospital Clínico Universitario de Santiago de Compostela, Travesía Choupana s/n, 15706, Santiago de Compostela, Spain.
Piñeiro
Roberto
R
Blanco
Montserrat
M
Gallego
Rosalía
R
Diéguez
Carlos
C
Gualillo
Oreste
O
González-Juanatey
José R
JR
Lago
Francisca
F
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001667:Binding, Competitive; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D003561:Cytarabine / Q000494:pharmacology; D003593:Cytoplasm / Q000737:chemistry / Q000378:metabolism; D054439:Ghrelin; D013006:Growth Hormone / Q000494:pharmacology; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D051379:Mice; D032383:Myocytes, Cardiac / Q000378:metabolism*; D036361:Peptide Hormones / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D043562:Receptors, G-Protein-Coupled / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D054440:Receptors, Ghrelin; D020133:Reverse Transcriptase Polymerase Chain Reaction
D054439:Ghrelin; D036361:Peptide Hormones; D012333:RNA, Messenger; D043562:Receptors, G-Protein-Coupled; D054440:Receptors, Ghrelin; D003561:Cytarabine; D013006:Growth Hormone