Ana M. Rodríguez-López

Nitric oxide is involved in apoptosis induced by thapsigargin in rat mesangial cells.

The purpose of this study was to examine the mechanisms of thapsigargin-induced apoptosis in rat glomerular mesangial cells and the possible involvement of nitric oxide (NO) in this process. In mesangial cell monolayers incubated for 12 h in a medium without growth factors and with 10–6 M thapsigargin, a known specific inhibitor of endoplasmic reticulum Ca2+-ATPase, a high percentage of cells showed typical nuclear features of apoptosis, assessed either by staining with propidium iodide (23 vs. 9% in control conditions) or by terminal desoxynucleotidyl transferase-mediated dUTP biotin nick end labelling (TUNEL; 17 vs. 5% in control conditions). When cells were maintained in a medium containing 10% fetal calf serum (FCS) or in a free-calcium medium, the thapsigargin-induced apoptosis rate was very low. In rat mesangial cells treatment with thapsigargin decreased the expression of BCL-2 protein and bcl-2 mRNA, whereas it did not alter the levels of BAX protein or bax mRNA. When mesangial cells were incubated with thapsigargin in the absence of FCS, we detected a significant increase in nitrite production (3.78 ± 0.96 vs. 1.76 ± 0.44 μmol/well). Furthermore, the treatment with the NO synthesis inhibitor L-NAME (10–4 M) induced a significant decrease in the number of apoptotic cells (9%), whereas incubation with the NO donor SIN-1 (10–5 M) induced a marked increase in the rate of apoptosis (29%). Western and Northern blot analysis of macrophage-type inducible NO synthase (iNOS) demonstrated that thapsigargin treatment induces the expression of the iNOS protein and iNOS mRNA. Treatment with L-NAME prevented the thapsigargin-induced BCL-2 decrease, whereas incubation with SIN-1 potentiated the effect of thapsigargin on BCL-2. Double labelling by immunohistochemistry for iNOS and TUNEL revealed that the same cells that suffered apoptosis were positive for iNOS. In summary, our results indicate that thapsigargin is able to enhance the apoptosis rate of rat mesangial cells by a mechanism that is mediated by an increase in cytosolic free calcium. Increased iNOS expression, and hence increased NO production, seems to be involved in this effect.

Effects of captopril, losartan, and nifedipine on cell hypertrophy of cultured vascular smooth muscle from hypertensive Ren-2 transgenic rats

We hypothesized that tissular renin‐angotensin system (RAS) induces vascular hypertrophy in hypertensive Ren‐2 transgenic rats (TGR; strain name TGR(mRen2)L27). This assumption was tested in cell cultures of vascular smooth muscle (VSMC) from both hypertensive TGR and control normotensive Sprague‐Dawley (SD) rats. Planar cell surface area, protein synthesis, and protein content per cell were studied, the role for locally produced angiotensin II (AII) was evaluated and the possible pharmacological interference by different drugs was analysed. By use of radioimmunoassay techniques, AII could be determined in TGR cultures (10.25±0.12 pg per 107 cells) while it could not be detected in SD ones. Under serum‐free conditions, VSMC from hypertensive TGR were hypertrophic when compared to SD VSMC, as they presented a higher protein content per cell (335±18 and 288±7 pg per cell respectively; P<0.05) and increased mean planar cell surface area, as determined by image analysis (4,074±238 and 4,764±204 μm2, respectively; P<0.05). When exogenously added to cultured SD and TGR VSMC, AII (100 pM to 1 μM) promoted protein synthesis and protein content in a concentration‐dependent manner without affecting DNA synthesis. Maximal effects were observed at 100 nM. At this concentration, AII effectively increased planar cell surface area in both SD and TGR cultures by ∼20%. Treatment of TGR cultures, in the absence of exogenous AII, with the angiotensin‐converting enzyme inhibitor captopril or the angiotensin AT1 receptors antagonist losartan (100 nM to 10 μM) reduced planar cell surface area in a concentration‐dependent manner. In addition, both captopril and losartan (10 μM), decreased protein synthesis by ∼15%. Treatment of SD VSMC, in the absence of exogenous AII, with both captopril and losartan had no effect either on planar cell surface area or protein synthesis. Treatment with the Ca2+ antagonist nifedipine (100 nM to 10 μM) reduced cell size in both SD and TGR cultures. Maximal cell reduction reached by nifedipine averaged 906±58 and 1,292±57 μm2, in SD and TGR, respectively (P<0.05). In addition, nifedipine, nitrendipine and nisoldipine (all at 10 μM) decreased protein synthesis in both cell types by 15–25%. We concluded that cultured VSMC from TGR are hypertrophic in comparison with those from SD. This cell hypertrophy can be the consequence of the expression of the transgene Ren‐2 that activates a tissular RAS and locally produces AII, which acts in a paracrine, autocrine, or intracrine manner. Cell hypertrophy in TGR cultures could be selectively reduced by RAS blockade, while nifedipine decreased cell size and protein synthesis in both hypertrophic and non hypertrophic cells.

Effect of Hypothalamic-Hypophysary Inhibitory Factor on Mesangial Cell Activation

We examined the effect of a sodium pump inhibitor isolated from bovine hypothalamus and pituitary tissues on contraction, proliferation, and calcium mobilization in primary cultures of rat mesangial cells. Hypothalamic-hypophysary inhibitory factor (HHIF) inhibited rubidium uptake in a concentration-dependent manner (0.2 U/mL: 56.8 +/- 6.3% inhibition). It also induced a concentration- and time-dependent decrease in planar cell surface area. Maximal contraction (25 +/- 5% reduction in cell size) was reached at 60 minutes with a concentration of 0.2 U/mL. This effect was inhibited by both verapamil and TMB-8 (10(-5) mol/L). HHIF was also observed to increase DNA synthesis (0.2 U/mL: 4361 +/- 168 versus 2129 +/- 162 cpm per well under control conditions) and cell proliferation (0.2 U/mL: 52,290 +/- 1931 versus 10,512 +/- 121 cells per well under control conditions). Both effects were also inhibited by verapamil and TMB-8. Moreover, HHIF induced the expression of immediate early genes c-fos and c-jun mRNA. HHIF-induced effects were accompanied by an increase in cytosolic free calcium (203 +/- 58 versus 101 +/- 2 nmol/L under control conditions), which was inhibited by verapamil and TMB-8. In summary, HHIF induces mesangial cell contraction and proliferation; these effects seem to be mediated by an increase in cytosolic free calcium levels.

Effect of Verapamil on Endothelin-1-Induced Proliferation in Cultured Rat Mesangial Cells

The effect of verapamil, a calcium channel blocker, on endothelin-1 (ET-l)-induced mesangial cell proliferation was assayed. Rat mesangial cells (primary cultures) were maintained in 0.5% fetal calf s

Endogenous Angiotensin II and Cell Hypertrophy in Vascular Smooth Muscle Cultures from Hypertensive Ren-2 Transgenic Rats

We investigated the possible role of a tissular renin-angiotensin system in promoting the growth of vascular smooth muscle cells (VSMCs) from hypertensive transgenic rats (TGRs) with the mouse renin gene Ren-2. Mean arterial pressure values were 99.4 ± 2.8 and 186.7 ± 5.0 mm Hg for control Sprague-Dawley rats (SDs) and TGRs, respectively (p < 0.05). The tunica media of femoral arteries obtained from hypertensive TGRs was found to be thickened compared to that of age-matched normotensive SDs. Agiotensin II could be detected by dot blot and immunocytochemistry and quantified by radioimmunoassay in transgenic VSMCs, but not in control SD ones. Under serum-free conditions, VSMCs derived from TGRs showed a higher protein content than those derived from SDs (337 ± 19 vs. 269 ± 14 pg/cell, p < 0.05, n = 3). Under the same basal conditions, the mean planar cell surface area was significantly higher in TGR VSMCs than in SD ones (4,764 ± 204 vs. 4,074 ± 238 µm2, p < 0.05). In addition, TGR VSMCs showed an enhanced [14C]-leucine uptake but SD VSMCs did not (13,188 ± 663 vs. 7,633 ± 713 dpm/well, p < 0.05). VSMCs showed a concentration-dependent proliferative response to fetal calf serum (FCS) that was more marked in TGRs than in SDs. In the absence of FCS, c-fos and c-jun mRNAs were expressed only in transgenic cultures. From the present results, we can hypothesize that cultured TGR VSMCs are able to synthesize angiotensin II that, being almost exclusive into the cells, contributes to produce VSMC growth in the absence of FCS stimulation.

Tubular Cell Apoptosis and Proliferation in the Early Phase of Renal Damage in Uninephrectomized SHR

In the present study, we measured tubular cell apoptosis and proliferation and Bcl-2 expression during the early phase (3 months) of the process of renal fibrosis in the experimental model of uninephrectomized spontaneously hypertensive rats (SHR). Tubulointerstitial fibrosis was evaluated by automated quantitative morphometry using selective staining of the extracellular matrix with sirius red. Apoptosis was quantified by both in situ dUTP biotin nick end-labeling method (TUNEL) and by propidium iodide staining. Proliferation rate was measured by counting cells expressing the proliferating cell nuclear antigen. Bcl-2 expression was assessed by immunohistochemistry. Tubulointerstitial fibrosis increased progressively during the 3 months of follow-up. Proliferation and apoptosis rates in tubular cells increased from the first to the second month after UNX. In the third month after UNX, the proliferating tubular cell number continued to increase, whereas the apoptotic cell number was maintained, coinciding with an increase in the expression of Bcl-2. Our observations demonstrate a different profile of tubular cell proliferation and apoptosis during the genesis of early tubulointerstitial damage in UNX-SHR.

The effect of LU-49938 (nexopamil) on the activation by serotonin of mesangial cells.

Summary— Intraglomerular platelet activation may release vasoactive agents such as serotonin (5‐hydroxytryptamine, 5‐HT) that may affect local hemodynamics and promote mesangial proliferation, eventually leading to glomerular sclerosis. The main purpose of this study is to analyze whether nexopamil, a verapamil derivative, with the property of blocking simultaneously calcium channels and 5‐HT2 receptors, could modify the contractile and mitogenic effects of serotonin on cultured rat mesangial cells. Serotonin caused a concentration‐dependent increase in [3H]thymidine incorporation into DNA, and mesangial cell proliferation. The effects of 5‐HT on thymidine uptake and cell proliferation were blocked by the selective 5‐HT2 receptor blocker ketanserin 10−5 M. Nexopamil abolished in a concentration‐dependent way the serotonin‐induced [3H]thymidine incorporation into DNA, and the serotonin‐induced increase in number of cells. Using 5‐HT 10−4 or 10−5 M, nexopamil had significant effects at concentration above 10−7 M. Serotonin induced a concentration‐ and time‐dependent reduction of planar cell surface area. This effect was also completely blocked by ketanserin. Nexopamil partially blocked the serotonin‐induced mesangial cell contraction, in a dose‐dependent manner. All these data suggest that nexopamil inhibits both 5‐HT‐induced mesangial cell contraction and proliferation by blocking 5‐HT2 receptors and the voltage‐operated Ca2+ channels.