Intracellular free calcium abnormalities in fibroblasts from non-insulin-dependent diabetic patients with and without arterial hypertension

Intranasal Insulin Improves Age-Related Cognitive Deficits and Reverses Electrophysiological Correlates of Brain Aging

Peripheral insulin resistance is a key component of metabolic syndrome associated with obesity, dyslipidemia, hypertension, and type 2 diabetes. While the impact of insulin resistance is well recognized in the periphery, it is also becoming apparent in the brain. Recent studies suggest that insulin resistance may be a factor in brain aging and Alzheimer's disease (AD) whereby intranasal insulin therapy, which delivers insulin to the brain, improves cognition and memory in AD patients. Here, we tested a clinically relevant delivery method to determine the impact of two forms of insulin, short-acting insulin lispro (Humalog) or long-acting insulin detemir (Levemir), on cognitive functions in aged F344 rats. We also explored insulin effects on the Ca(2+)-dependent hippocampal afterhyperpolarization (AHP), a well-characterized neurophysiological marker of aging which is increased in the aged, memory impaired animal. Low-dose intranasal insulin improved memory recall in aged animals such that their performance was similar to that seen in younger animals. Further, because ex vivo insulin also reduced the AHP, our results suggest that the AHP may be a novel cellular target of insulin in the brain, and improved cognitive performance following intranasal insulin therapy may be the result of insulin actions on the AHP.

A novel signaling pathway: fibroblast nicotinic receptor alpha1 binds urokinase and promotes renal fibrosis

The nicotinic acetylcholine receptor alpha1 (nAChRalpha1) was investigated as a potential fibrogenic molecule in the kidney, given reports that it may be an alternative urokinase (urokinase plasminogen activator; uPA) receptor in addition to the classical receptor uPAR. In a mouse obstructive uropathy model of chronic kidney disease, interstitial fibroblasts were identified as the primary cell type that bears nAChRalpha1 during fibrogenesis. Silencing of the nAChRalpha1 gene led to significantly fewer interstitial alphaSMA(+) myofibroblasts (2.8 times decreased), reduced interstitial cell proliferation (2.6 times decreased), better tubular cell preservation (E-cadherin 14 times increased), and reduced fibrosis severity (24% decrease in total collagen). The myofibroblast-inhibiting effect of nAChRalpha1 silencing in uPA-sufficient mice disappeared in uPA-null mice, suggesting that a uPA-dependent fibroblastic nAChRalpha1 pathway promotes renal fibrosis. To further establish this possible ligand-receptor relationship and to identify downstream signaling pathways, in vitro studies were performed using primary cultures of renal fibroblasts. (35)S-Labeled uPA bound to nAChRalpha1 with a K(d) of 1.6 x 10(-8) m, which was displaced by the specific nAChRalpha1 inhibitor d-tubocurarine in a dose-dependent manner. Pre-exposure of uPA to the fibroblasts inhibited [(3)H]nicotine binding. The uPA binding induced a cellular calcium influx and an inward membrane current that was entirely prevented by d-tubocurarine preincubation or nAChRalpha1 silencing. By mass spectrometry phosphoproteome analyses, uPA stimulation phosphorylated nAChRalpha1 and a complex of signaling proteins, including calcium-binding proteins, cytoskeletal proteins, and a nucleoprotein. This signaling pathway appears to regulate the expression of a group of genes that transform renal fibroblasts into more active myofibroblasts characterized by enhanced proliferation and contractility. This new fibrosis-promoting pathway may also be relevant to disorders that extend beyond chronic kidney disease.

P2X(7) Receptors as a Transducer in the Co-Occurrence of Neurological/Psychiatric and Cardiovascular Disorders: A Hypothesis

Background. Over-stimulation of the purinergic P2X₇ receptor may bring about cellular dysfunction and injury in settings of neurodegeneration, chronic inflammation, as well as in psychiatric and cardiovascular diseases. Here we speculate how P2X₇ receptor over-activation may lead to the co-occurrence of neurological and psychiatric disorders with cardiovascular disorders. Presentation. We hypothesize that proinflammatory cytokines, in particular interleukin-1β, are key players in the pathophysiology of neurological, psychiatric, and cardiovascular diseases. Critically, this premise is based on a role for the P2X₇ receptor in triggering a rise in these cytokines. Given the broad distribution of P2X₇ receptors in nervous, immune, and vascular tissue cells, this receptor is proposed as central in linking the nervous, immune, and cardiovascular systems. Testing. Investigate, retrospectively, whether a bidirectional link can be established between illnesses with a proinflammatory component (e.g., inflammatory and chronic neuropathic pain) and cardiovascular disease, for example, hypertension, and whether patients treated with anti-inflammatory drugs have a lower incidence of disease complications. Positive outcome would indicate a prospective study to evaluate therapeutic efficacy of P2X₇ receptor antagonists. Implications. It should be stressed that sufficient direct evidence does not exist at present supporting our hypothesis. However, a positive outcome would encourage the further development of P2X₇ receptor antagonists and their application to limit the co-occurrence of neurological, psychiatric, and cardiovascular disorders.

Increased store-operated and 1-oleoyl-2-acetyl-sn-glycerol-induced calcium influx in monocytes is mediated by transient receptor potential canonical channels in human essential hypertension

OBJECTIVE

Activation of nonselective cation channels of the transient receptor potential canonical (TRPC) family has been associated with hypertension. Whether store-operated channels, which are activated after depletion of intracellular stores, or second-messenger-operated channels, which are activated by 1-oleoyl-2-acetyl-sn-glycerol, are affected in essential hypertension is presently unknown.

METHODS

Using a polymerase chain reaction, an in-cell western assay and the fluorescent dye technique we studied TRPC3, TRPC5, and TRPC6 expression and store-operated and 1-oleoyl-2-acetyl-sn-glycerol-induced calcium influx into human monocytes in 19 patients with essential hypertension and in 17 age-matched and sex-matched normotensive control individuals.

RESULTS

We observed a significantly increased expression of TRPC3 and TRPC5, but not TRPC6, in essential hypertension. Store-operated calcium influx was significantly elevated in essential hypertension. Store-operated calcium influx was reduced by the inhibitor 2-aminoethoxydiphenylborane, specific TRPC3 and TRPC5 knockdown, but not TRPC6 knockdown using gene silencing by RNA interference. 1-Oleoyl-2-acetyl-sn-glycerol-induced calcium influx and barium influx were also significantly elevated in essential hypertension. The 1-oleoyl-2-acetyl-sn-glycerol-induced cation influx was reduced by TRPC3 and TRPC5 knockdown.

CONCLUSION

We demonstrated an increased TRPC3 and TRPC5 expression and a subsequently increased store-operated calcium influx and increased 1-oleoyl-2-acetyl-sn-glycerol-induced cation influx in monocytes of patients with essential hypertension. This increased activation of monocytes through TRPC channels in patients with essential hypertension may promote vascular disease in these patients.

Intracellular calcium and sodium-lithium countertransport in type 2 diabetic patients with and without albuminuria

Increased intracellular calcium concentrations ([Ca(2+)](i)) and enhanced sodium-lithium countertransport (Na/Li CT) activities may play a role in the development of diabetic complications such as diabetic nephropathy. The present study was designed to test the hypothesis that albuminuria in patients with type 2 diabetes is associated with increased [Ca(2+)](i) in response to stimulation with platelet-activating factor (PAF) or with enhanced Na/Li CT activities. The study population comprised 203 type 2 diabetic patients. Albuminuria was defined as an albumin excretion rate exceeding 30 mg/d (117 cases). PAF-evoked rises in [Ca(2+)](i) and Na/Li CT activities were determined in Epstein-Barr-virus-immortalized lymphoblasts. Albuminuria was related to high stimulated [Ca(2+)](i) but not to high basal [Ca(2+)](i). The association was independent of age, sex and several non-diabetes related confounders, but depended on diabetes-related factors, such as the duration of diabetes. The risk of albuminuria was highest in subjects with high [Ca(2+)](i) who reported a diabetes duration of < or =10 years. There was no association between Na/Li CT activities and albuminuria. The present results support the hypothesis that albuminuria in type 2 diabetic patients is associated with a primary defect in intracellular calcium homeostasis. The association between stimulated [Ca(2+)](i) and albuminuria is most prominent in early diabetes.

Hydrogen peroxide is an endothelium-derived hyperpolarizing factor in animals and humans

Vascular endothelium plays an important role in maintaining vascular homeostasis by synthesizing and releasing several vasodilating factors, such as prostacyclin, nitric oxide (NO), and a yet unidentified endothelium-derived hyperpolarizing factor (EDHF). Possible candidates for EDHF include epoxyeicosatrienoic acids, endothelium-derived K(+) ions, and as we have recently identified, hydrogen peroxide (H(2)O(2)). Electrical communication between endothelial and smooth muscle cells through gap junctions has also been suggested to be involved in endothelium-dependent hyperpolarization. Among the above candidates, the H(2)O(2) hypothesis well explains the pathophysiological interactions between NO and EDHF and re-highlights the physiological roles of the reactive oxygen species in endothelium-dependent vascular responses. This brief review summarizes our current knowledge about H(2)O(2) as an EDHF, with special reference to its production by the endothelium, its action on membrane potentials and its pathophysiological roles.

Low Ca(2+) pump activity in diabetic nephropathy

Elevated cell Na(+)-H(+) exchange (NHE) activity characterizes diabetic nephropathy (DN), but the mechanisms of this abnormality are unclear. Recent evidence suggests that NHE and the Ca(2+) pump share similar regulatory pathways, but whether abnormalities in Ca(2+) metabolism characterize DN is not known. We investigated Ca(2+) efflux rates, NHE activity, cytosolic Ca(2+) ([Ca(2+)](i)) concentrations, and intracellular pH (pH(i)) in human skin fibroblasts from 20 patients with type 1 (insulin-dependent) diabetes and nephropathy; 20 patients with diabetes with normoalbuminuria matched for age, sex, and duration of diabetes; and 10 individuals without diabetes. Ca(2+) pump-mediated Ca(2+) efflux was significantly lower in patients with nephropathy than in patients with normoalbuminuria and individuals without diabetes (0.074 +/- 0.01 versus 0.115 +/- 0.01 versus 0.131 +/- 0.02 nmol.mg(protein)(-1).min(-1); analysis of variance [ANOVA], P = 0.015). Elevated maximal velocity of the Na(+)-H(+) exchanger was confirmed in fibroblasts from patients with nephropathy (14.4 +/- 1.2 versus 7.1 +/- 0.7 versus 8.0 +/- 1.2 mmol H(+).l cell(-1).min(-1); ANOVA, P < 0.0001). A reverse correlation between Ca(2+) pump activity and NHE rates could be shown. Adjustment for glycated hemoglobin and plasma lipid levels did not affect these findings. Finally, [Ca(2+)](i) concentrations and pH(i) were normal in all patients. Low Ca(2+) pump activity is a concomitant event of elevated NHE rates in DN; the molecular dysfunction(s) underlying these abnormalities remains to be established.

G protein beta 3 subunit 825T allele, hypertension, obesity, and diabetic nephropathy

The 825T allele of the gene GNB3 which encodes the beta 3 subunit of heterotrimeric G proteins is associated with enhanced signal transduction via G proteins through the generation of a splice variant termed Gbeta3s. It was detected following a classical candidate gene approach using cell lines from patients with enhanced signal transduction and essential hypertension. The high frequency of the 825T allele in 'old' ethnicities, e.g. bushmen and Australian aborigines as well as in black populations, together with its strong association with obesity suggests that the 825T allele is a true 'thrifty genotype'. Development of obesity associated with the 825T allele is strongly influenced by lifestyle, e.g. physical activity, and other exogenous influences like pregnancy. In hypertension the 825T allele is associated with low renin activity and appears to strongly predict the development of left ventricular hypertrophy. In type 2 diabetes the 825T allele was reported to be predispose for end-stage renal disease, whereas this effect has not yet been confirmed for patients with type 1 diabetes.

Modulatory effect of insulin on release of calcium from human fibroblasts by angiotensin II

BACKGROUND

Angiotensin II stimulates synthesis and deposition of collagen and might contribute to the vascular and cardiac dysfunction associated with arterial hypertension. Insulin attenuates angiotensin II-induced responses of intracellular Ca2+ concentration ([Ca2+]) in many cell types but this effect is less in insulin-resistant states. The mechanisms of the interaction between insulin and angiotensin II are still not known.

OBJECTIVE

To characterize the effects of angiotensin II on intracellular [Ca2+] and the effects of insulin on the angiotensin II-induced response of intracellular [Ca2+] in human skin fibroblasts.

METHODS

Spectrofluorophotometric measurements of intracellular [Ca2+] in monolayers of cultured human skin fibroblasts from 15 normotensive patients were performed using Fura-2 at 510 nm emission with excitation wavelengths of 340 and 380 nm.

RESULTS

Basal intracellular [Ca2+] in quiescent (24 h serum-deprived) human fibroblasts was 75 +/- 3 nmol/l (n = 20). Administration of angiotensin II elevated intracellular [Ca2+] dose-dependently with a concentration for half-maximal effect of 20 nmol/l. Administration of 100 nmol/l angiotensin II stimulated a rapid and transient increase in intracellular [Ca2+] (from 75 +/- 3 to 130 +/- 2 nmol/l, n = 20). Removal of extracellular calcium did not change peak intracellular [Ca2+], but it did reduce the time to recovery of [Ca2+] (from 64 +/- 4 to 48 +/- 2 s, n = 10, P < 0.01), suggesting that an angiotensin II-induced transmembrane calcium influx had occurred. This hypothesis was confirmed by quenching studies with manganese. The angiotensin II-induced changes in intracellular [Ca2+] were completely blocked by administration of 100 nmol/l of the angiotensin II type 1 receptor inhibitor losartan but not by administration of 100 nmol/l of the angiotensin II type 2 receptor blocker CGP42112A. Acute (20 min) exposure to 100 nmol/l insulin did not alter basal intracellular [Ca2+] in quiescent fibroblasts, but significantly blunted angiotensin II-stimulated peak of [Ca2+] (to 101 +/- 3 nmol/l, P < 0.01, n = 18) and delayed recovery of [Ca2+] (to 99 +/- 5 s, P < 0.01). The inhibitory effect of insulin was observed both with and without extracellular Ca2+.

CONCLUSIONS

Our results demonstrate that administration of angiotensin II increases intracellular [Ca2+] in human skin fibroblasts by release of Ca2+ from intracellular Ca2+ stores and by influx of Ca2+ and that administration of insulin attenuates the response of [Ca2+] to angiotensin II but prolongs the time to recovery of [Ca2+].