Effect of hyperglycemia on the basal cytosolic free calcium level, calcium signal and tyrosine-phosphorylation in human T-cells

TRPA1 Covalent Ligand JT010 Modifies T Lymphocyte Activation

Transient Receptor Potential Ankyrin 1 (TRPA1) is a non-selective cation channel involved in sensitivity to a plethora of irritating agents and endogenous mediators of oxidative stress. TRPA1 influences neuroinflammation and macrophage and lymphocyte functions, but its role is controversial in immune cells. We reported earlier a detectable, but orders-of-magnitude-lower level of Trpa1 mRNA in monocytes and lymphocytes than in sensory neurons by qRT-PCR analyses of cells from lymphoid organs of mice. Our present goals were to (a) further elucidate the expression of Trpa1 mRNA in immune cells by RNAscope in situ hybridization (ISH) and (b) test the role of TRPA1 in lymphocyte activation. RNAscope ISH confirmed that Trpa1 transcripts were detectable in CD14+ and CD4+ cells from the peritoneal cavity of mice. A selective TRPA1 agonist JT010 elevated Ca2+ levels in these cells only at high concentrations. However, a concentration-dependent inhibitory effect of JT010 was observed on T-cell receptor (TcR)-induced Ca2+ signals in CD4+ T lymphocytes, while JT010 neither modified B cell activation nor ionomycin-stimulated Ca2+ level. Based on our present and past findings, TRPA1 activation negatively modulates T lymphocyte activation, but it does not appear to be a key regulator of TcR-stimulated calcium signaling.

Toward Development of a Diabetic Synovium Culture Model

Osteoarthritis (OA) is a degenerative joint disease characterized by articular cartilage degradation and inflammation of synovium, the specialized connective tissue that envelops the diarthrodial joint. Type 2 diabetes mellitus (DM) is often found in OA patients, with nearly double the incidence of arthritis reported in patients with diabetes (52%) than those without it (27%). The correlation between OA and DM has been attributed to similar risk factors, namely increasing age and joint loading due to obesity. However, a potential causative link is not well understood due to comorbidities involved with treating diabetic patients, such as high infection rates and poor healing response caused by hyperglycemia and insulin resistance. The purpose of this study was to investigate the effect of hyperglycemic and insulin culture conditions on synovium properties. It was hypothesized that modeling hyperglycemia-induced insulin resistance in synovium would provide novel insights of OA pathogenesis in DM patients. To simulate DM in the synovial joint, healthy synovium was preconditioned in either euglycemic (EG) or hyperglycemic (HG) glucose concentrations with insulin in order to induce the biological response of the diseased phenotype. Synovium biochemical composition was evaluated to determine ECM remodeling under hyperglycemic culture conditions. Concurrent changes in AKT phosphorylation, a signaling pathway implicated in insulin resistance, were measured along with gene expression data for insulin receptors, glucose transporters, and specific glycolysis markers involved in glucose regulation. Since fluid shear stress arising during joint articulation is a relevant upstream stimulus for fibroblast-like synoviocytes (FLS), the predominant cell type in synovium, FLS mechanotransduction was evaluated via intracellular calcium ([Ca²⁺]_i). Incidence and length of primary cilia, a critical effector of cell mechanosensing, were measured as potential mechanisms to support differences in [Ca²⁺]_i responses. Hyperglycemic culture conditions decreased collagen and GAG content compared to EG groups, while insulin recovered ECM constituents. FLS mechanosensitivity was significantly greater in EG and insulin conditions compared to HG and non-insulin treated groups. Hyperglycemic treatment led to decreased incidence and length of primary cilia and decreased AKT phosphorylation, providing possible links to the mechanosensing response and suggesting a potential correlation between glycemic culture conditions, diabetic insulin resistance, and OA development.

Presence of TRPA1 Modifies CD4+/CD8+ T Lymphocyte Ratio and Activation

Transient Receptor Potential Ankyrin 1 (TRPA1) has been reported to influence neuroinflammation and lymphocyte function. We analysed the immune phenotype and activation characteristics of TRPA1-deficient mice (knockout—KO) generated by targeted deletion of the pore-loop domain of the ion channel. We compared TRPA1 mRNA and protein expression in monocyte and lymphocyte subpopulations isolated from primary and secondary lymphatic organs of wild type (WT) and KO mice. qRT-PCR and flow cytometric studies indicated a higher level of TRPA1 in monocytes than in lymphocytes, but both were orders of magnitude lower than in sensory neurons. We found lower CD4+/CD8+ thymocyte ratios, diminished CD4/CD8 rates, and B cell numbers in the KO mice. Early activation marker CD69 was lower in CD4+ T cells of KO, while the level of CD8+/CD25+ cells was higher. In vitro TcR-mediated activation did not result in significant differences in CD69 level between WT and KO splenocytes, but lower cytokine (IL-1β, IL-6, TNF-α, IL-17A, IL-22, and RANTES) secretion was observed in KO splenocytes. Basal intracellular Ca²⁺ level and TcR-induced Ca²⁺ signal in T lymphocytes did not differ significantly, but interestingly, imiquimod-induced Ca²⁺ level in KO thymocytes was higher. Our results support the role of TRPA1 in the regulation of activation, cytokine production, and T and B lymphocytes composition in mice.

Chronic Hyperglycemia Drives Functional Impairment of Lymphocytes in Diabetic INSC94Y Transgenic Pigs

People with diabetes mellitus have an increased risk for infections, however, there is still a critical gap in precise knowledge about altered immune mechanisms in this disease. Since diabetic INSC94Y transgenic pigs exhibit elevated blood glucose and a stable diabetic phenotype soon after birth, they provide a favorable model to explore functional alterations of immune cells in an early stage of diabetes mellitus in vivo. Hence, we investigated peripheral blood mononuclear cells (PBMC) of these diabetic pigs compared to non-diabetic wild-type littermates. We found a 5-fold decreased proliferative response of T cells in INSC94Y tg pigs to polyclonal T cell mitogen phytohemagglutinin (PHA). Using label-free LC-MS/MS, a total of 3,487 proteins were quantified, and distinct changes in protein abundances in CD4+ T cells of early-stage diabetic pigs were detectable. Additionally, we found significant increases in mitochondrial oxygen consumption rate (OCR) and higher basal glycolytic activity in PBMC of diabetic INSC94Y tg pigs, indicating an altered metabolic immune cell phenotype. Thus, our study provides new insights into molecular mechanisms of dysregulated immune cells triggered by permanent hyperglycemia.

Is type 2 diabetes mellitus an inverse risk factor for the development of rheumatoid arthritis?

Type 2 diabetes mellitus (T2DM) and rheumatoid arthritis (RA) are both chronic diseases. Although the link between metabolic abnormalities and dysregulated inflammation has received much attention, it is not known whether T2DM can be a risk for the development of RA. Also, observational studies have the disadvantage that the possibility of confounding factors, such as environmental factors, cannot be ruled out. Therefore, the current study performed the mendelian randomization (MR) analysis using recent large-scale genome-wide association studies datasets of T2DM and RA separately European and Asian ancestries. As a result, T2DM had an inverse causal effect on the risk of RA. This study proposed a novel hypothesis that a protective effect of T2DM for the risk of RA.

Ameliorated Autoimmune Arthritis and Impaired B Cell Receptor-Mediated Ca2+ Influx in Nkx2-3 Knock-out Mice

B cells play a crucial role in the pathogenesis of rheumatoid arthritis. In Nkx2-3-deficient mice (Nkx2-3^−/−) the spleen’s histological structure is fundamentally changed; therefore, B cell homeostasis is seriously disturbed. Based on this, we were curious, whether autoimmune arthritis could be induced in Nkx2-3^−/− mice and how B cell activation and function were affected. We induced arthritis with immunization of recombinant human proteoglycan aggrecan G1 domain in Nkx2-3^−/− and control BALB/c mice. We followed the clinical picture, characterized the radiological changes, the immune response, and intracellular Ca²⁺ signaling of B cells. Incidence of the autoimmune arthritis was lower, and the disease severity was milder in Nkx2-3^−/− mice than in control BALB/c mice. The radiological changes were in line with the clinical picture. In Nkx2-3^−/− mice, we measured decreased antigen-induced proliferation and cytokine production in spleen cell cultures; in the sera, we found less anti-CCP-IgG2a, IL-17 and IFNγ, but more IL-1β, IL-4 and IL-6. B cells isolated from the lymph nodes of Nkx2-3^−/− mice showed decreased intracellular Ca²⁺ signaling compared to those isolated from BALB/c mice. Our findings show that the transcription factor Nkx2-3 might regulate the development of autoimmune arthritis most likely through modifying B cell activation.

Putting Together the Pieces: A Metabolic Model of Viral Infection and the Subsequent Development of Asthma

While the prevalence of asthma and atopic disease continues to rise over the past half a century, the exact mechanism behind this remains elusive. Of late, the role of metabolic dysfunction in disease is becoming more clearly classified. The part of metabolic dysfunction in respiratory viral infections is studied, which reopens the debate in the role of infection on asthma development in childhood. During infection, there is a rapid shift in nutrients available for immune cells to metabolize. Exploring these metabolic changes and the resulting immune cell function, a striking pattern emerges. In asthma development following viral infection, it is proposed there is a transient state of impaired glucose tolerance resulting in a sudden increase in glucose for lymphocytes to metabolize, triggering them to enter a state of increased aerobic glycolysis. Reviewing this outcome, along with previous work, a new working metabolic model of asthma development is proposed by suggesting a new step between a healthy immune system and asthma.

Hyperglycemic condition influence on mineral trioxide aggregate biocompatibility and biomineralization

This study aimed to investigate in vitro and in vivo the influence of hyperglycemic condition on biocompatibility and biomineralization of gray mineral trioxide aggregate (GMTA) and white mineral trioxide aggregate (WMTA). For the in vitro study, fibroblast-like cells L929 were cultured under high or normal glucose concentration to investigate the effects of both MTA's on cell proliferation and inflammatory cytokines production IL-1β, IL-6, and TNF-α. For the in vivo study, polyethylene tubes containing MTA materials and empty tubes were implanted into dorsal connective tissues of Wistar rats previously assigned normal and hyperglycemic. After 7 and 30 days, the tubes with surrounding tissues were removed and subjected to histological, fluorescence and immunohistochemical analyzes of IL-1β, IL-6, and TNF-α. In vitro study showed that, under high glucose condition, GMTA reduced cell proliferation and IL-6 production compared with WMTA. Moreover, in vivo study revealed that hyperglycemic condition did not modify the inflammatory response and cytokines production in the tissue close to both materials. Independently of hyperglycemic status, mineralized areas were observed with both materials, but the fluorescence intensity of WMTA was diminished on 14 days in hyperglycemic animals. It is possible to conclude that GMTA was able to inhibit the proliferation rate and IL-6 production under high glucose concentration in vitro. Furthermore, cytokines production and inflammatory response were not upregulated in hyperglycemic animals; however, a decrease in the calcium deposition was observed in presence of WMTA, suggesting a delay in the mineralization process.

Hyperglycemia Induces Osteoclastogenesis and Bone Destruction Through the Activation of Ca2+/Calmodulin-Dependent Protein Kinase II

Hyperglycemia induces osteoclastogenesis and bone resorption through complicated, undefined mechanisms. Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) promotes osteoclastogenesis, and could be activated by hyperglycemia. Here, we investigated whether CaMKII is involved in hyperglycemia-induced osteoclastogenesis and subsequent bone resorption. Osteoclast formation, bone resorption, CaMKII expression and phosphorylation were measured under high glucose in vitro and in streptozotocin-induced hyperglycemia rats with or without CaMKII inhibitor KN93. The results showed that 25 mmol/L high glucose in vitro promoted cathepsin K and tartrate-resistant acid phosphatase expression (p < 0.05) and osteoclast formation (p < 0.01) associated with enhancing β isoform expression (p < 0.05) and CaMKII phosphorylation (p < 0.001). Hyperglycemia promoted the formation of osteoclasts and resorption of trabecular and alveolar bone, and inhibited sizes of femur and mandible associated with enhanced CaMKII phosphorylation (p < 0.001) in rats. All these changes could be alleviated by KN93. These findings imply that CaMKII participates not only in hyperglycemia-induced osteoclastogenesis and subsequent bone resorption, but also in the hyperglycemia-induced developmental inhibition of bone.

T cell activation and cardiovascular risk in type 2 diabetes mellitus: a protocol for a systematic review and meta-analysis

INTRODUCTION

The burden of non-communicable diseases such as type 2 diabetes mellitus (T2DM) and cardiovascular diseases (CVDs) has drastically increased in developing countries over the years. Although recent evidence points to chronic immune activation to be a significant aspect in the pathogenesis and development of T2DM and CVDs, the exact role of T cells is not fully understood. Therefore, we aim to investigate T cell function and cardio vascular risk in T2DM. In addition, the therapeutic effect of blood glucose-lowering drugs to reverse hyperglycaemia induced T cell dysfunction and myocardial infarction will be reviewed.

METHODS

This will be a systematic review and meta-analysis of published studies assessing T cell activation and cardiovascular risk in adults with T2DM. The search strategy will include medical subject headings (MeSH) words for PubMed/MEDLINE database. The search terms will also be adapted to grey literature, Embase and Cochrane Central Register of Controlled Trials electronic databases. Studies will be independently screened by two reviewers using predefined criteria. Relevant eligible full texts will be screened and data will be extracted. Data extraction will be performed using a pre-piloted structured form. To assess the quality and strengths of evidence across selected studies, the Grading of Recommendations Assessment Development and Evaluation approach will be used. The Cochran's Q statistic and the I2 statistics will be used to analyse statistical heterogeneity between studies. If included studies show substantial level of statistical heterogeneity, a random-effects meta-analysis will be performed using R statistical software.

DISCUSSIONS

This review will not require ethical approval, and the findings will be disseminated through peer-reviewed publication and conferences. Although other previous studies have reported deregulated T cell function in hyperglycaemia, the underlying mechanisms remain controversial. However, evidence suggests that T cells may be a key component in the development of T2DM and CVDs as its complication. Furthermore, they are a potential diagnostic and therapeutic target in the management of the disease.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42018099745.

Immunomodulation at epithelial sites by obesity and metabolic disease

Obesity and related type 2 diabetes are increasing at epidemic proportions globally. It is now recognized that inflammatory responses mediated within the adipose tissue in obesity are central to the development of disease. Once initiated, chronic inflammation associated with obesity leads to the modulation of immune cell function. This review will focus specifically on the impact of obesity on γδ T cells, a T-cell subset that is found in high concentrations in epithelial tissues such as the skin, intestine, and lung. Epithelial γδ T cell function is of particular concern in obesity as they are the guardians of the epithelial barrier and mediate repair. A breakdown in their function, and subsequently the deterioration of the epithelium can result in dire consequences for the host. Obese patients are more prone to non-healing injuries, infection, and disease. The resulting inflammation from these pathologies further perpetuates the disease condition already present in obese hosts. Here we will provide insight into the immunomodulation of γδ T cells that occurs in the epithelial barrier during obesity and discuss current therapeutic options.

Fine-tuning of proximal TCR signaling by ZAP-70 tyrosine residues in Jurkat cells

Zeta-chain-associated protein kinase of 70kDa (ZAP-70) kinase is a key regulator in the early steps of TCR signaling but some aspects of its fine regulation are still unclear. From its 31 tyrosine (Y) residues, 11 phosphorylation sites have been identified, some with activator (Y315 and Y493) or inhibitory (Y292 and Y492) and others with unknown function (Y069, Y126 and Y178). In our present work, we aimed to elucidate the role of different Y residues of ZAP-70, especially those with unknown function, in calcium signaling and the autoregulation of the kinase. ZAP-70-deficient Jurkat cells (P116) were stably reconstituted with point-mutated ZAP-70 constructs where tyrosine residues 069, 126, 178, 238, 292, 315, 492 or 493 were replaced with phenylalanine (F). The anti-CD3-elicited calcium signal increased in F069-, F292- and F492-ZAP-70-expressing cell lines but decreased in the F126-, F315- and F493-ZAP-70-expressing cell lines. ZAP-70 point mutations led to phosphorylation changes predominantly in SH2 domain containing leukocyte protein of 76kDa (SLP-76) but not linker of activated T cells (LAT) during CD3-activation; moreover, we detected basal hyperphosphorylation of SLP-76 Y128 in the F126-, F178- and F492-ZAP-70-expressing cell lines. In summary, Y069, Y178, Y292 and Y492 have inhibitory, while Y126, Y315 and Y493 activator role in anti-CD3-induced T-cell activation. Phosphorylation changes in LAT and SLP-76 suggest that fine regulation of ZAP-70 on calcium signaling is rather transmitted through SLP-76 not LAT. Additionally, negative or positive autoregulatory function of Y292 and Y493 or Y315, respectively, was revealed in ZAP-70. These data indicate that previously not characterized Y069, Y126 and Y178 in ZAP-70 participate in the fine regulation of TCR signaling.

The involvement of sphingosine kinase 1 in LPS-induced Toll-like receptor 4-mediated accumulation of HIF-1α protein, activation of ASK1 and production of the pro-inflammatory cytokine IL-6

Toll-like receptors (TLRs) lie in the core of resistance to infectious diseases allowing host immune cells to specifically detect pathogens by recognising their specific molecular patterns. Cell membrane-associated TLR4 (recognises lipopolysaccharide (LPS) of Gram-negative bacteria) and endosomal TLR7/8 (recognise viral single-stranded RNA) are known to activate hypoxia inducible factor-1α (HIF-1α) protein (necessary for cellular adaptation to the inflammatory stress) via redox-dependent mechanism. TLR4 triggers the cross talk between HIF-1α and apoptosis signal-regulating kinase 1 (ASK1), whereas TLR7/8 activates HIF-1α in the ASK1-independent manner. Here, we report that in THP-1 and RAW264.7 macrophages, ligand-induced activation of the TLR4 but not TLR7/8 induces activation and transcriptional upregulation of sphingosine kinase 1 (SphK1) in extracellular signal-regulating kinase and phospholipase C-1γ/PI3 kinase-dependent manner. TLR4-mediated SphK1 activation was found to be critical for the redox-dependent activation of HIF-1α and ASK1, as well as for the prevention of LPS-induced activation of caspase 3 and the expression of pro-inflammatory cytokine interleukin-6.

Calcium is required for coelomocyte activation in earthworms

The role of calcium signaling in activation of both innate and adaptive immunity is basically important, however, the evolutionary aspects are not clarified yet. Currently limited data are available about calcium levels of coelomocytes, cellular mediators of earthworm immunity. We aimed to observe basal and induced Ca(2+) levels of coelomocyte subgroups after various stimulations in Eisenia fetida and Allolobophora caliginosa using a Ca(2+)-sensitive dye. E. fetida chloragocytes had the highest basal Ca(2+) levels among subpopulations; however there was no detectable Ca(2+) influx after any stimuli, while coelomocytes showed strong Ca(2+) increase after ionomycin treatment, which could be attenuated using phorbol ester. A. caliginosa coelomocytes showed a weak response to ionophore, while chloragocytes, similar to those in E. fetida, exhibited no changes after this stimulation. Intracellular calcium is mainly stored in the endoplasmic reticulum of coelomocytes as proved by thapsigargin treatments. Among several mitogens only phytohemagglutinin caused increased Ca(2+) level in E. fetida coelomocytes, but not in A. caliginosa coelomocytes. Moreover, the chemoattractant fMLP revealed calcium influx of Eisenia coelomocytes. For the first time we observed various basal Ca(2+) levels and sensibility to Ca(2+) influx inducers (including mitogens and chemoattractant) of coelomocyte subgroups using flow cytometry. These observations suggest that Ca(2+) influx and signal transduction may play crucial roles in the innate immunity of the earthworm.

Gliclazide Attenuates the Intracellular Ca2+Changes InducedIn Vitroby Ischemia in the Retinal Slices of Rats with Streptozotocin-Induced Diabetes

PURPOSE

To investigate the dynamics of the intracellular Ca2+ concentration ([Ca2+]i) during retinal ischemia in rats with streptozotocin (STZ)-induced diabetes and the effect of gliclazide, a sulfonylurea with a potent free-radical scavenging activity on ischemia-induced [Ca2+]i dynamics.

METHODS

Rats with STZ (65 mg/kg) induced diabetes were divided into three groups: the untreated diabetic group, the gliclazide-treated group, and the glibenclamide-treated group. An ischemic condition was imposed in vitro on the retinal slices by perfusion with an oxygen/glucose deprived solution. The [Ca2+]i was measured in individual layers of the rat retinal slices loaded with the Ca2+ indicator fluo-3.

RESULTS

As compared to that in the normal rat retina, both the amplitude and the kinetics of the [Ca2+]i increase were suppressed in the intermediate layers of the retinal slices from the diabetic rats under the ischemic condition. These changes were attenuated by the administration of gliclazide but not by that of glibenclamide.

CONCLUSIONS

Hyperglycemia influences ischemia-induced [Ca2+]i dynamics predominantly in the intermediate layers of the retina, and gliclazide, as compared to glibenclamide without a free radical scavenging activity, potently attenuates the ischemia-induced changes in the calcium dynamics.

High glucose initiates calpain-induced necrosis before apoptosis in LLC-PK1 cells

Cells exposed to high ambient glucose concentrations are subject to increases in intracellular calcium ([Ca(2+)](i)). We therefore considered it likely that the calcium-dependent cysteine protease calpain would play a role in the development of high glucose-induced cell injury. After 3 and 24 h, high glucose concentrations (25 mM D-glucose) produced almost identical increases in the degree of necrotic cell death in kidney proximal tubular epithelial cells (LLC-PK(1)) compared to cells treated with control glucose (5 mM D-glucose). Necrotic cell death could be restricted by inhibiting the activity of calpain. High glucose-treated LLC-PK(1) cells were found to have significantly elevated [Ca(2+)](i) concentrations within 1 h, and elevated calpain activity within 2 h compared to control treated cells. The DNA nick sensor poly(ADP-ribose) polymerase (PARP) has previously been shown to be an important driver of high glucose-induced cell death, but here we found that although PARP activity was increased after 24 h, it was unaltered after 3 h. Furthermore, PARP inhibition with PJ-34 did not restrict early high glucose-induced necrosis. Using a gene knockdown strategy with small interference RNA, we found that silencing calpain was effective in reducing the degree of early high glucose-induced necrosis. We conclude that high glucose concentrations evoke an early, calpain-mediated necrosis in cultured proximal tubular cells that is PARP-independent, and precedes the previously recognized activation of apoptosis.

Intermolecular relations between the glucocorticoid receptor, ZAP-70 kinase, and Hsp-90

The glucocorticoid receptor (GR) participates in both genomic and non-genomic glucocorticoid hormone (GC) actions by interacting with other cytoplasmic signalling proteins. Previously, we have shown that high dose Dexamethasone (DX) treatment of Jurkat cells causes tyrosine phosphorylation of ZAP-70 within 5 min in a GR-dependent manner. By using co-immunoprecipitation and confocal microscopy, here we demonstrate that the liganded GR physically associates with ZAP-70, in addition to its phosphorylation changes. The association of the ligand-bound GR and ZAP-70 was also observed in HeLa cells transfected with ZAP-70, suggesting that this co-clustering is independent of lymphocyte specific factors. Furthermore, the ZAP-70 was found to also co-precipitate with Hsp-90 chaperone both in Jurkat and transgenic HeLa cells, independent of the presence of DX. These findings raise the possibility that ZAP-70 may serve as an important link between GC and TcR-induced signaling, thereby transmitting non-genomic GC action in T-cells.

Controlling hyperglycemia as an adjunct to cancer therapy

Hyperglycemia is commonly manifested in cancer patients. Although high intakes of sugar and refined carbohydrates and elevated blood glucose are strongly associated with the risk of cancer, much less is known about their effects on survival after cancer diagnosis. There is evidence that high carbohydrate intake is associated with poorer survival after diagnosis for early breast cancer. We measured glycated hemoglobin in a group of cancer patients (some with active disease and some in remission) and found a statistically significant lower average blood glucose in those in remission. Glycated hemoglobin provides an indication of average blood glucose over 2 to 3 months. The authors discuss lifestyle changes including diet and physical activity that can reduce average blood glucose. Ascorbic acid (AA) supplementation as an adjunct to cancer therapy is also considered. Furthermore, they present a biologically plausible explanation for how hyperglycemia can impair the actions of AA and damage immune effectiveness and hinder cancer survival. One mechanism is likely a reduction in intracellular AA; high intracellular levels of AA are necessary for optimal activity of the hexose monophosphate shunt. This metabolic pathway is important for maintaining proper cellular antioxidant status in immune cells including lymphocytes involved in cell-mediated immunity.

Antagonist of growth hormone-releasing hormone induces apoptosis in LNCaP human prostate cancer cells through a Ca2+-dependent pathway

Antagonists of growth hormone-releasing hormone (GHRH) exert antiproliferative effects directly on cancer cells, which are mediated by the tumoral GHRH receptors. However, the signal transduction pathways involved in antiproliferative effect of GHRH antagonists have not yet been elucidated. We used flow cytometry to investigate whether GHRH antagonist JV-1-38 can induce changes in the cytosolic free Ca2+ concentration leading to apoptosis in LNCaP human prostate cancer cells. JV-1-38 evoked prompt Ca2+ signal in a dose-dependent way (1-10 microM) and induced early stage of apoptosis in LNCaP human prostate cancer cells at a concentration effective in suppression of cell proliferation (10 microM) peaking after 3 h. Unexpectedly, agonist GHRH(1-29)NH2, which elevates cytosolic free Ca2+ concentration in pituitary somatotrophs at nanomolar concentrations, failed to induce Ca2+ signal or apoptosis even at a 10-fold higher concentration (100 microM). However, agonist GHRH(1-29)NH2 inhibited JV-1-38-induced Ca2+ signals in a dose-dependent way without affecting the antagonist-induced apoptosis. Peptides unrelated to GHRH did not induce Ca2+ signals in LNCaP human prostate cancer cells. EDTA (10 mM) or nifedipine (10 microM) significantly reduced the Ca2+ signal and early stage of apoptosis induced by JV-1-38, supporting the view that the increase in intracellular Ca2+ in response to JV-1-38 occurs primarily through extracellular Ca2+ entry through voltage-operated Ca2+ channels. In conclusion, GHRH antagonists activate tumoral GHRH receptors and are able to induce apoptosis in LNCaP human prostate cancer cells through a Ca2+-dependent pathway. Treatment with GHRH antagonists may offer a new approach to the therapy of prostate and other hormone-sensitive cancers.

Elevation of basal intracellular calcium as a central element in the activation of brain macrophages (microglia): suppression of receptor-evoked calcium signaling and control of release function

Microglia-brain macrophages are immune-competent cells of the CNS and respond to pathologic events. Using bacterial lipopolysaccharide (LPS) as a tool to activate cultured mouse microglia, we studied alterations in the intracellular calcium concentration ([Ca 2+]i) and in the receptor-evoked generation of transient calcium signals. LPS treatment led to a chronic elevation of basal [Ca 2+]i along with a suppression of evoked calcium signaling, as indicated by reduced [Ca 2+]i transients during stimulation with UTP and complement factor 5a. Presence of the calcium chelator BAPTA prevented the activation-associated changes in [Ca 2+]i and restored much of the signaling efficacy. We also evaluated downstream consequences of a basal [Ca 2+]i lifting during microglial activation and found BAPTA to strongly attenuate the LPS-induced release of nitric oxide (NO) and certain cytokines and chemokines. Furthermore, microglial treatment with ionomycin, an ionophore elevating basal [Ca 2+]i, mimicked the activation-induced calcium signal suppression but failed to induce release activity on its own. Our findings suggest that chronic elevation of basal [Ca 2+]i attenuates receptor-triggered calcium signaling. Moreover, increased [Ca 2+]i is required, but by itself is not sufficient, for release of NO and certain cytokines and chemokines. Elevation of basal [Ca 2+]i could thus prove a central element in the regulation of executive functions in activated microglia.