Koh-ichi Yuhki

Effects of the prostanoids on the proliferation or hypertrophy of cultured murine aortic smooth muscle cells

Effects of the prostanoids on the growth of cultured aortic vascular smooth muscle cells (VSMCs) were examined using mice lacking prostanoid receptors. Proliferation of VSMCs was assessed by measuring [3H]‐thymidine incorporation and the cell number, and their hypertrophy by [14C]‐leucine incorporation and protein content. In VSMCs from wild‐type mice, expressions of mRNAs for the EP4 and TP were most abundant, followed by those for the IP, EP3 and FP, when examined by competitive reverse transcriptase‐PCR. Those for the EP1, EP2 and DP, however, could not be detected. AE1‐329, an EP4 agonist, and cicaprost, an IP agonist, inhibited platelet derived growth factor (PDGF)‐induced proliferation of VSMCs from wild‐type mice; these inhibitory effects disappeared completely in VSMCs from EP4−/− and IP−/− mice, respectively. In accordance with these effects, AE1‐329 and cicaprost stimulated cAMP production in VSMCs from wild‐type mice, which were absent in VSMCs from EP4−/− and IP−/− mice, respectively. Effects of PGE2 on cell proliferation and adenylate cyclase were almost similar with those of AE1‐329 in VSMCs from wild‐type mice, which disappeared in VSMCs from EP4−/− mice. PGD2 inhibited PDGF‐induced proliferation of VSMCs from both wild‐type and DP−/− mice to a similar extent. This action of PGD2 was also observed in VSMCs from EP4−/− and IP−/− mice. In VSMCs from wild‐type mice, I‐BOP, a TP agonist, showed potentiation of PDGF‐induced hypertrophy. I‐BOP failed to show this action in VSMCs from TP−/− mice. The specific agonists for the EP1, EP2 or EP3, and PGF2α showed little effect on the growth of VSMCs. These results show that PGE2, PGI2 and TXA2 modulate PDGF‐induced proliferation or hypertrophy of VSMCs via the EP4, IP and TP, respectively, and that the inhibitory effect of PGD2 on PDGF‐induced proliferation is not mediated by the DP, EP4 or IP.

Endothelin-1 production is enhanced by rotenone, a mitochondrial complex I inhibitor, in cultured rat cardiomyocytes.

In chronic heart failure and acute myocardial infarction, the tissue level of endothelin (ET) -1 in the heart, as well as its plasma level, has been reported to increase markedly. There is, however, little information about what in these pathologic conditions leads to increased production of ET-1, and which type of cell in the heart produces ET-1. We examined the mRNA and peptide expression of ET-1 using cultured rat neonatal cardiomyocytes, in which mitochondrial dysfunction was induced by rotenone, a mitochondrial respiratory chain complex I inhibitor, because one of the common features in failing or ischemic hearts is an alteration in energy metabolism due to mitochondrial dysfunction. Rotenone increased glucose use by the culture cells within 12 h of addition without affecting cell viability, and depressed the mitochondrial membrane potential after 72 h, indicating the induction of mitochondrial dysfunction in cardiomyocytes. Rotenone induced significant increase in the expression level of mRNA for ET-1 within 1 h of addition. In accordance with this finding, immunoreactive ET-1 in culture medium increased 3 times after 24 h of incubation, suggesting active secretion of ET-1 from cultured cells treated with rotenone. Immunocytochemical analysis verified significant increase of ET-1 peptide in cardiomyocytes, confirming the production of ET-1 by cardiomyocytes. These results suggest that derangement of mitochondrial function in cardiomyocytes itself could lead to the increased production of ET-1 in cardiomyocytes, and that this mechanism may contribute to the increased production of ET-1 in failing and ischemic hearts.

Fat, keeping the heart healthy?

The hormone adiponectin is secreted from fat cells and increases sensitivity to insulin in muscle and liver; adiponectin increases resistance to metabolic disorders and, it now appears, may also protect heart tissue when blood flow is restricted (pages 1096–1103).