Inhibition of intracellular Ca2+ mobilisation by low antiproliferative concentrations of thapsigargin in human vascular smooth-muscle cells

Sorcin is involved during embryo implantation via activating VEGF/PI3K/Akt pathway in mice

Our earlier studies have demonstrated the cyclic variation and also the altered expression of sorcin in endometrium during early-to-mid-secretory phase transition in women with unexplained infertility. The current study was undertaken to establish the functional role of sorcin in endometrial receptivity in mice. Results indicated that sorcin was highly expressed during the window of implantation in mice and functional blockage of sorcin caused significant reduction in number of implanted blastocyst. The receptivity markers (i.e.Integrin β3, HBEGF, IGFBP1, WNT4 and Cyclin E)) were found to be downregulated in sorcin knocked down uterine horn on day 5 as compared to untreated horn. The reduced attachment and expansion of BeWo spheroids on RL95-2 endometrial cells with sorcin knock down, in in vitro model of endometrium-trophoblast interaction further supported these findings. Uterine sorcin expression pattern during estrous cycle and in delayed implantation mice model suggested the upregulation of sorcin by estrogen. The functional blockade of sorcin induced the intracellular Ca⁺² levels in endometrial epithelial cells (EECs), which indicated that altered Ca⁺² homeostasis might be responsible for implantation failure. Sorcin silencing led to significant reduction in the expression of angiogenic factor VEGF and its downstream effector molecules i.e. PI3K, Akt and NOS. The migratory and invasive properties of HUVECs were abrogated by anti-VEGF or by adding culture media from sorcin blocked EECs, which indicated that sorcin might mediate angiogenesis during implantation. Taken together, sorcin is involved in the regulation of Ca⁺²-mediated angiogenesis via VEGF/PI3K/Akt pathway in endometrial cells and plays a crucial role in preparing the endometrium for implantation.

The Chlamydia trachomatis Inclusion Membrane Protein CpoS Counteracts STING-Mediated Cellular Surveillance and Suicide Programs

Evading cell death is critical for Chlamydia to maintain a replicative niche, but the underlying mechanisms are unknown. We screened a library of Chlamydia mutants for modulators of cell death. Inactivation of the inclusion membrane protein CpoS (Chlamydia promoter of survival) induced rapid apoptotic and necrotic death in infected cells. The protection afforded by CpoS is limited to the inclusion in which it resides, indicating that it counteracts a spatially restricted pro-death signal. CpoS-deficient Chlamydia induced an exacerbated type I interferon response that required the host cGAS/STING/TBK1/IRF3 signaling pathway. Disruption of STING, but not cGAS or IRF3, attenuated cell death, suggesting that STING mediates Chlamydia-induced cell death independent of its role in regulating interferon responses. CpoS-deficient strains are attenuated in their ability to propagate in cell culture and are cleared faster from the murine genital tract, highlighting the importance of CpoS for Chlamydia pathogenesis.

Low nanomolar thapsigargin inhibits the replication of vascular smooth muscle cells through reversible endoplasmic reticular stress

Thapsigargin (TG), an inhibitor of Ca(2+) ATPase pumps in the endoplasmic reticulum (ER), inhibits replication of human vascular smooth muscle cell (hVSMC) at low nM concentrations. TG blocks replication of other cell types through promotion of ER stress (ERS). In order to determine whether ERS may mediate the cytostatic effect of TG in hVSMCs, the effect of TG on ERS in hVSMCs was studied by assessing markers of ERS: Immunoglobulin Heavy Chain Binding Protein (BiP), growth inhibitory transcription factor, GADD153, phosphorlylated eukaryotic initiation factor 2α (p-eIF2α) and phosphorlylated protein kinase R (p-PKR). hVSMCs derived from saphenous veins were rendered quiescent with serum-free medium for 96 h incubated with 10 nM TG at 37 °C for 24 h, then washed free of TG and incubated with 10% foetal calf serum (FCS) for a further 24 h. At selected times, BiP, GADD153, p-eIF2α, p-PKR and cyclin D1 expression was assessed. TG promoted a marked increase in BiP and GADD153, but suppressed cyclin D1 mRNA and protein expression. Under serum-free conditions p-eIF2α and p-PKR expression was not enhanced by TG. 15-24 h After removal of TG all these factors returned to levels seen in control cells. These data demonstrate that the inhibitory effect of 10nM TG on hVSMC replication is mediated through induction of ERS and associated factors that cessate replication and is reversible. These observations have implications in the aetiology and treatment of diseases that include atherogenesis, vein graft failure and restenosis.

A novel imaging-based high-throughput screening approach to anti-angiogenic drug discovery

The successful progression to the clinic of angiogenesis inhibitors for cancer treatment has spurred interest in developing new classes of anti-angiogenic compounds. The resulting surge in available candidate therapeutics highlights the need for robust, high-throughput angiogenesis screening systems that adequately capture the complexity of new vessel formation while providing quantitative evaluation of the potency of these agents. Available in vitro angiogenesis assays are either cumbersome, impeding adaptation to high-throughput screening formats, or inadequately model the complex multistep process of new vessel formation. We therefore developed an organotypic endothelial-mural cell co-culture assay system that reflects several facets of angiogenesis while remaining compatible with high-throughput/high-content image screening. Co-culture of primary human endothelial cells (EC) and vascular smooth muscle cells (vSMC) results in assembly of a network of tubular endothelial structures enveloped with vascular basement membrane proteins, thus, comprising the three main components of blood vessels. Initially, EC are dependent on vSMC-derived VEGF and sensitive to clinical anti-angiogenic therapeutics. A subsequent phenotypic VEGF-switch renders EC networks resistant to anti-VEGF therapeutics, demarcating a mature vascular phenotype. Conversely, mature EC networks remain sensitive to vascular disrupting agents. Therefore, candidate anti-angiogenic compounds can be interrogated for their relative potency on immature and mature networks and classified as either vascular normalizing or vascular disrupting agents. Here, we demonstrate that the EC-vSMC co-culture assay represents a robust high-content imaging high-throughput screening system for identification of novel anti-angiogenic agents. A pilot high-throughput screening campaign was used to define informative imaging parameters and develop a follow-up dose-response scheme for hit characterization. High-throughput screening using the EC-vSMC co-culture assay establishes a new platform to screen for novel anti-angiogenic compounds for cancer therapy.

The pro-apoptotic substance thapsigargin selectively stimulates re-growth of brain capillaries

Thapsigargin is a pro-apoptotic chemical, which has been shown to be useful to study cell death of cholinergic or dopaminergic neurons, or cells, which degenerate in Alzheimer's disease or Parkinson's disease, respectively. The aim of the present work was to study the effects of thapsigargin in the well established organotypic brain co-slice model composed of the basal nucleus of Meynert (nBM), ventral mesencephalon (vMes), dorsal striatum (dStr) and parietal cortex (Ctx). Cholinergic acetyltransferase-positive neurons in the nBM and dStr and dopaminergic tyrosine hydroxylase-positive neurons in the vMes survived, when cultured for 4 weeks with nerve growth factor and glial cell line-derived neurotrophic factor. Nerve fibers of cholinergic nBM neurons grew into the cortex and dopaminergic nerve fibers sprouted into dopamine D2 receptor-positive dStr. The whole co-slice contained a dense laminin-positive capillary network. Treatment of co-cultures with 3 microM thapsigargin for 24 hr significantly decreased the number of cholinergic neurons and dopaminergic neurons. This cell death displayed apoptotic DAPI-positive malformed nuclei and enhanced TUNEL-positive cells. Thapsigargin selectively stimulated the laminin-positive capillary growth between the nBM and Ctx. In conclusion, the induced cell death of cholinergic and dopaminergic neurons may be accompanied by enhanced angiogenic activity.

Bartonella-induced endothelial cell proliferation is mediated by release of calcium from intracellular stores

The facultative intracellular bacterium Bartonella henselae induces unique angiogenic lesions in immunocompromised hosts. To determine the role of intracellular calcium pools in B. henselae-induced endothelial cell proliferation, we generated B. henselae-conditioned medium (BCM) and tested the ability of these cell-free proteins to induce human umbilical vein endothelial cell (HUVEC) proliferation, CXCL8 production, and intracellular Ca2+ signals. HUVECs incubated with BCM for 3 days had higher cell numbers than controls. In addition, HUVECs produced increased amounts of CXCL8 in response to BCM when compared to medium controls. When BCM was added to HUVECs and the intracellular Ca2+ response measured with the calcium-sensitive dye fura-2/AM, a Ca2+ rise was demonstrated. It was determined that this Ca2+ rise originated from intracellular Ca2+ stores through the use of the Ca2+ ATPase inhibitor thapsigargin. Further, it was demonstrated that BCM enhanced CXCL8 production and HUVEC proliferation in a Ca2+-dependent manner. Conditioned medium from B. henselae causes an intracellular Ca2+ rise in HUVECs, which is involved in B. henselae-induced HUVEC proliferation and CXCL8 production. These results implicate intracellular Ca2+ pools in B. henselae-induced angiogenesis and may lead to increased understanding of the mechanisms of pathogen-induced angiogenesis.

Calcium and the replication of human vascular smooth muscle cells: studies on the activation and translocation of extracellular signal regulated kinase (ERK) and cyclin D1 expression

Since the precise role of sarcoplasmic reticular Ca2+ in mediating vascular smooth muscle cells (VSMC) proliferation is unknown, the effect of pre-incubation with thapsigargin on extracellular signal regulated kinase (ERK) activation, the translocation of activated of ERK 1/2 to the nucleus, cyclin D1 expression, the onset of S phase and cytosolic Ca2+ levels were studied. Human saphenous vein VSMCs (hVSMC) were incubated with 10 nM thapsigargin for 24 h followed by stimulation with fetal calf serum and the activation of ERK1/2 and cyclin D1 assessed by western blotting, the intracellular distribution of ERK1/2 using indirect immunofluorescence, the onset of S-phase with the incorporation of bromodeoxyuridine and sarcoplasmic reticular Ca2+ status using FURA-2. Thapsigargin had a marginal effect on ERK1/2 activation only at 5 min and 10 min after stimulation with fetal calf serum. In contrast, the rapid translocation of ERK1/2 to the nucleus was completely blocked by thapsigargin. S phase was delayed by 8 h by thapsigargin which co-incided with the recovery of cytosolic Ca2+ levels and cyclin D1 expression. It is concluded that the inhibitory effect of thapsigargin (depletion of Ca2+ pools) on hVSMC replication is mediated through the inhibition of translocation of activated ERK1/2 to the nucleus and not to the phosphorylation of ERK, per se, which in turn prevents cyclin D1 expression and thus progression of the cell cycle.

Effect of atorvastatin on intracellular calcium uptake in coronary smooth muscle cells from diabetic pigs fed an atherogenic diet

Intracellular Ca(2+) store loading has been shown to alter proliferation and apoptosis of several cell types. In addition, HMG-CoA reductase inhibitors (i.e. atorvastatin) are effective in treating diabetic dyslipidemic patients. Thus, we hypothesized that chronic atorvastatin treatment would prevent increased Ca(2+) uptake into intracellular Ca(2+) stores in vascular smooth muscle cells from diabetic dyslipidemic pigs. Male Yucatan pigs were divided into four groups for 20 weeks-- (1) low fat fed (control); (2) hyperlipidemic (F); (3) alloxan-induced diabetic dyslipidemic (DF); and (4) diabetic dyslipidemic pigs treated with atorvastatin (DFA). The F, DF, and DFA groups were fed a high fat/cholesterol diet. Cells were isolated from the coronary artery and the myoplasmic Ca(2+) (Ca(m)) response measured using single cell fura-2 imaging. The Ca(m) response to caffeine (5 mM to release Ca(2+) from the sarcoplasmic reticulum, SR) and ionomycin (10 microM; to release the total Ca(2+) store) was determined in either the presence of low Na (19Na; inhibits Na(+)-Ca(2+) exchange), thapsigargin (TSG; inhibits the SR Ca(2+) pump), and a 19Na+TSG solution. Low Na induced the uptake of Ca(2+) into both SR and non-SR Ca(2+) stores in the DF group, but not the DFA group. Furthermore, after depletion of the SR Ca(2+) store with TSG, 19Na evoked Ca(2+) uptake into non-SR Ca(2+) stores in all three groups except in the DFA group. In summary, this study demonstrates that atorvastatin prevents the enhanced uptake of Ca(2+) by SR and non-SR Ca(2+) stores in diabetic dyslipidemic pigs.

Smooth muscle cell response to mechanical injury involves intracellular calcium release and ERK1/ERK2 phosphorylation

We have investigated possible signaling pathways coupled to injury-induced ERK1/2 activation and the subsequent initiation of vascular rat smooth muscle cell migration and proliferation. Aortic smooth muscle cells were cultured to confluency and subjected to in vitro injury under serum-free conditions. In fluo-4-loaded cells, injury induced a rapid wave of intracellular Ca(2+) release that propagated about 200 microm in radius from the injured zone, reached a peak in about 20 s, and subsided to the baseline within 2 min. The wave was abolished by prior treatment with the sarcoplasmic reticulum ATPase inhibitor thapsigargin, but not by omission of extracellular Ca(2+). ERK1/2 activation reached a peak at 10 min after injury and was inhibited by the MEK1 inhibitor PD98059, as well as by thapsigargin, fluphenazine, genistein, and the Src inhibitor PP2. These inhibitors also reduced [(3)H]thymidine incorporation and migration of cells into the injured area determined at 48 h after injury. These results show that mechanical injury to vascular smooth muscle cells induces a Ca(2+) wave which is dependent on intracellular Ca(2+) release. Furthermore, the injury activates ERK1/2 phosphorylation as well as cell migration and replication.