Activation of cAMP signaling transiently inhibits apoptosis in vascular smooth muscle cells in a site upstream of caspase-3

Intracellular signaling pathways that are involved in protection of vascular smooth muscle cells (VSMC) from apoptosis remain poorly understood. This study examines the effect of activators of cAMP/cGMP signaling on apoptosis in non-transfected VSMC and in VSMC transfected with c-myc (VSMC-MYC) or with its functional analogue, E1A-adenoviral protein (VSMC-E1A). Serum-deprived VSMC-E1A exhibited the highest apoptosis measured as the content of chromatin and low molecular weight DNA fragments, phosphatidylserine content in the outer surface of plasma membrane and caspase-3 activity (ten-, five-, four- and tenfold increase after 6 h of serum withdrawal, respectively). In VSMC-E1A, the addition of an activator of adenylate cyclase, forskolin, abolished chromatin cleavage, DNA laddering, caspase-3 activation and the appearance of morphologically-defined apoptotic cells triggered by 6 h of serum deprivation. In non-transfected VSMC and in VSMC-MYC, 6 h serum deprivation led to approximately six- and threefold activation of chromatin cleavage, respectively, that was also blocked by forskolin. In VSMC-E1A, inhibition of apoptosis was observed with other activators of cAMP signaling (cholera toxin, isoproterenol, adenosine, 8-Br-cAMP), whereas 6 h incubation with modulators of cGMP signaling (8-Br-cGMP, nitroprusside, atrial natriuretic peptide, L-NAME) did not affect the development of apoptotic machinery. The antiapoptotic effect of forskolin was abolished in 24 h of serum deprivation that was accompanied by normalization of intracellular cAMP content and protein kinase A (PKA) activity. Protection of VSMC-E1A from apoptosis by forskolin was blunted by PKA inhibitors (H-89 and KT5720), whereas transfection of cells with PKA catalytic subunit attenuated apoptosis triggered by serum withdrawal. The protection of VSMC-E1A by forskolin from apoptosis was insensitive to modulators of cytoskeleton assembly (cytochalasin B, colchicine). Neither acute (30 min) nor chronic (24 h) exposure of VSMC to forskolin modified basal and serum-induced phosphorylation of the MAP kinase ERK1/2. Thus, our results show that activation of cAMP signaling delays the development of apoptosis in serum-deprived VSMC at a site upstream of caspase-3 via activation of PKA and independently of cAMP-induced reorganization of the cytoskeleton network and the ERK1/2-terminated MAPK signaling cascade

Na+/K+ pump and endothelial cell survival: [Na+]i/[K+]i-independent necrosis triggered by ouabain, and protection against apoptosis mediated by elevation of [Na+]i

Recent studies have demonstrated the tissue-specific effect of Na+/K+ pump inhibition by ouabain and other cardiac glycosides on cell viability. The vascular endothelium is an initial target of cardiac glycosides employed for the management of congestive heart failure as well as circulating endogenous ouabain-like substances (EOLS), the production of which is augmented in volume-expanded hypertension. This study examined the role of the Na+/K+ pump in the survival of cultured porcine aortic endothelial cells (PAEC). Complete Na+/K+ pump inhibition with ouabain led to PAEC death, indicated by cell detachment and decreased staining with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). Based on cell swelling and resistance to benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (z-VAD.fmk) a pan-caspase inhibitor, this type of cell death was classified as necrosis. In contrast to ouabain, Na+/K+ pump inhibition in K+-free medium did not affect PAEC viability and sharply attenuated apoptosis triggered by 3H decay-induced DNA damage. Necrosis evoked by ouabain was preserved after dissipation of the transmembrane gradient of K+ and Na+, whereas dissipation of the Na+ gradient abolished the antiapoptotic action of K+-free medium. Comparative analysis of these results and modulation of intracellular Na+ and K+ content by the above-listed stimuli showed that interaction of ouabain with Na+/K+-ATPase triggered necrosis independently of inhibition of Na+/K+ pump-mediated ion fluxes and inversion of the [Na+]i/[K+]i ratio, whereas protection against apoptosis under Na+/K+ pump inhibition in K+-depleted medium was mediated by [Na+]i elevation. The role of Na+/K+ pump-mediated regulation of endothelial cell survival and vascular remodelling seen in hypertension should be investigated further in context of EOLS and chronic treatment with digitalis

Catechin treatment improves cerebrovascular flow-mediated dilation and learning abilities in atherosclerotic mice

Severe dyslipidemia and the associated oxidative stress could accelerate the age-related decline in cerebrovascular endothelial function and cerebral blood flow (CBF), leading to neuronal loss and impaired learning abilities. We hypothesized that a chronic treatment with the polyphenol catechin would prevent endothelial dysfunction, maintain CBF responses, and protect learning abilities in atherosclerotic (ATX) mice. We treated ATX (C57Bl/6-LDLR(−/−) hApoB(+/+); 3 mo old) mice with catechin (30 mg·kg(−1)·day(−1)) for 3 mo, and C57Bl/6 [wild type (WT), 3 and 6 mo old] mice were used as controls. ACh- and flow-mediated dilations (FMD) were recorded in pressurized cerebral arteries. Basal CBF and increases in CBF induced by whisker stimulation were measured by optical coherence tomography and Doppler, respectively. Learning capacities were evaluated with the Morris water maze test. Compared with 6-mo-old WT mice, cerebral arteries from 6-mo-old ATX mice displayed a higher myogenic tone, lower responses to ACh and FMD, and were insensitive to NOS inhibition (P < 0.05), suggesting endothelial dysfunction. Basal and increases in CBF were lower in 6-mo-old ATX than WT mice (P < 0.05). A decline in the learning capabilities was also observed in ATX mice (P < 0.05). Catechin 1) reduced cerebral superoxide staining (P < 0.05) in ATX mice, 2) restored endothelial function by reducing myogenic tone, improving ACh- and FMD and restoring the sensitivity to nitric oxide synthase inhibition (P < 0.05), 3) increased the changes in CBF during stimulation but not basal CBF, and 4) prevented the decline in learning abilities (P < 0.05). In conclusion, catechin treatment of ATX mice prevents cerebrovascular dysfunctions and the associated decline in learning capacities

Apoptosis in serum-deprived vascular smooth muscle cells: evidence for cell volume-independent mechanism

Shrinkage is the earliest hallmark of cells undergoing apoptosis. This study examines the role of this phenomenon in the onset of vascular smooth muscle cell (VSMC) apoptosis triggered by growth factor withdrawal. In hyperosmotic media, VSMC showed the same amplitude of shrinkage but were more resistant to apoptosis than endothelial, epithelial and immune system cells. As with growth factor withdrawal, apoptosis in hyperosmotically-shrunken VSMC was sharply potentiated by transfection with E1A-adenoviral protein and was suppressed by activation of cAMP signaling as well as by the pan-caspase inhibitor z-VAD.fmk. Both cell shrinkage and apoptosis in VSMC-E1A treated with hyperosmotic medium were potentiated under sustained Na+, K+ pump inhibition with ouabain that was in contrast to inhibition of apoptosis documented in ouabain-treated, serum-deprived cells. After 1-hr incubation in serum-deprived medium, VSMC-E1A volume declined by approximately 15%. Transfer from hypotonic to control medium decreased VSMC-E1A volume by approximately 25% without any induction of apoptosis. Neither swelling in hyposmotic medium nor dissipation of the transmembrane gradient of K+ and major organic osmolytes protected serum-deprived VSMC-E1A from apoptosis. Thus, our results show that similarly to immune system, endothelial and epithelial cells, extensive VSMC shrinkage in hyperosmotic medium leads to the development of apoptosis. In contrast to hyperosmotic medium, the modest cell volume decrease occurring in serum-deprived VSMC does not contribute to triggering of the apoptotic machinery

Diabetologia

Aims/hypothesis: Tenascin-C (TN-C) is an extracellular matrix glycoprotein highly expressed in inflammatory and cardiovascular (CV) diseases. Serum TN-C has not yet been specifically studied in individuals with type 2 diabetes, a condition associated with chronic low-grade inflammation and increased CV disease risk. In this study, we hypothesised that elevated serum TN-C at enrolment in participants with type 2 diabetes would be associated with increased risk of death and major adverse CV events (MACE) during follow-up. Methods: We used a prospective, monocentric cohort of consecutive type 2 diabetes participants (the SURDIAGENE [SUivi Rénal, DIAbète de type 2 et GENEtique] cohort) with all-cause death as a primary endpoint and MACE (CV death, non-fatal myocardial infarction or stroke) as a secondary endpoint. We used a proportional hazard model after adjustment for traditional risk factors and the relative integrated discrimination improvement (rIDI) to assess the incremental predictive value of TN-C for these risk factors. Results: We monitored 1321 individuals (58% men, mean age 64 ± 11 years) for a median of 89 months. During follow-up, 442 individuals died and 497 had MACE. Multivariate Cox analysis showed that serum TN-C concentrations were associated with an increased risk of death (HR per 1 SD: 1.27 [95% CI 1.17, 1.38]; p < 0.0001) and MACE (HR per 1 SD: 1.23 [95% CI 1.13, 1.34]; p < 0.0001). Using TN-C concentrations on top of traditional risk factors, prediction of the risk of all-cause death (rIDI: 8.2%; p = 0.0006) and MACE (rIDI: 6.7%; p = 0.0014) improved significantly, but modestly. Conclusions/interpretation: In individuals with type 2 diabetes, increased serum TN-C concentrations were independently associated with death and MACE. Therefore, including TN-C as a prognostic biomarker could improve risk stratification in these individuals