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In addition to being an important component of the gap junction, connexin 43 (Cx43) has been shown to regulate other cellular functions, including cell proliferation. This regulatory role of Cx43 may be important in therapeutic situations, including wound healing or ischemic injuries. Caveolin‑1 (Cav‑1) has been shown to regulate angiogenesis. The aim of the present study was to analyze whether Cx43 counter‑regulates Cav‑1 in controlling the proliferation and migration of endothelial cells. The inhibition of Cx43 with niflumic acid, flufenamic acid and 18‑α‑glycyrrhetinic acid in cultured human umbilical vein endothelial cells resulted in decreased phosphorylation of extracellular signal‑regulated kinase (ERK)1/2 and increased expression of Cav‑1, as shown by western blot analysis. Furthermore, the inhibition of Cx43 resulted in a 50±7% decrease in cell proliferation, determined using a crystal violet assay, a 48±5% decrease in migration, determined using a migration assay, and a 49±6% decrease in endothelial tube formation, determined using a Matrigel assay, compared with the control. Similar results were obtained following specific inhibition of Cx43 by mimetic peptides (Gap26 and Gap27). Inhibition of the mitogen‑activated protein kinase kinase/ERK pathway with PD‑98059 resulted in an increased expression of Cav‑1 and a reduction in the expression of Cx43. Furthermore, cell proliferation, migration and tube formation in endothelial cells were impaired. By contrast, downregulation of the protein expression of Cav‑1 by small interference RNA resulted in increased expression of Cx43 and phosphorylation of ERK1/2. Accordingly, the number of cells in the Cav‑1 treated‑group increased by 35±5% compared with the controls. The data of the present study showed that Cav‑1 suppressed cell proliferation by inhibiting the activity of Cx43, which is upstream of ERK1/2. The downregulation of Cav‑1 protein resulted in loss of the inhibitory activity of Cav‑1 on cell proliferation and led to increased cell proliferation. This counter‑regulatory effect of Cx43 may be of importance in therapeutic angiogenesis.

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Aims: The study was aimed to investigate whether nicotine affects endothelial expression of PTHrP and PTHrP receptor, a peptide system involved in endothelial protection against apoptosis. Methods: Isolated and cultured rat coronary endothelial cells were used. Immunoblot techniques were used to study activation of mitogen-activated protein (MAP) kinases and to quantify PTHrP and PTHrP receptor expression. Real-time RT-PCR was used to quantify PTHrP, PTHrP-receptor, bcl-2, and bax mRNA expression. The rate of apoptosis was determined by HOE33258 staining and confirmed by quantification of the bcl-2-to-bax ratio. In vitro data were compared to hearts from rats exposed to cigarette smoking. Results: Nicotine induced PTHrP protein expression at nanomolar levels and small increases of PTHrP release (≈8%). Antagonists directed against the α7 subunit of cholinergic receptors, the most prominent isoform, attenuated nicotine-dependent increases of PTHrP expression. This effect of nicotine was p38 MAPK dependent. Nicotine at micromolar concentrations reduced PTHrP receptor expression. In vitro and in vivo we found a correlation between PTHrP receptor expression and bcl-2 expression. Conclusion: Nicotine induces PTHrP expression in endothelial cells but excessive concentrations of nicotine reduce PTHrP receptor expression thereby attenuating any protective effects of PTHrP against apoptosis.

Background: Pressure overload induces the cardiac expression of parathyroid hormone-related protein (PTHrP). Plasma levels are elevated in patients with heart disease. It is unknown whether this represents an epiphenomenon or suggests involvement in hypertrophy. Aim: To identify a potential role of PTHrP in pressure induced hypertrophy and heart failure. Methods and results: Pressure load was produced via thoracic aortic constriction (TAC) and application of a PTHrP antagonist (PTHrP(7-34)) via osmotic minipumps in mice. Main findings were confirmed in vitro by exposing isolated adult ventricular mice cardiomyocytes to PTHrP(1-34) (100 nmol/l). TAC treated animals developed myocardial hypertrophy within 2 weeks. The heart weight to body weight ratio increased from 5.02 ± 0.14 mg/g (sham/vehicle) and 5.16 ± 0.19 mg/g (sham/antagonist) to 6.59 ± 0.85 mg/g (TAC/vehicle) and 7.07 ± 0.80 mg/g (TAC/antagonist) (each n = 6-8; p b 0.05 for TAC vs. sham; not significantly different between TAC groups). In parallel, the expression of atrial natriuretic factor increased. Cardiac dysfunction (+ dP / dt, − dP / dt), however, was significantly lower in TAC mice receiving the antagonist, and SERCA2 expression was higher. Isolated cardiomyocytes exposed to PTHrP(1-34) developed reduced cell shortening. This reduction in cell function was abolished in the co-presence of the antagonist. Conclusion: PTHrP contributes to the progression of cardiac dysfunction in the pressure overloaded heart.