Renal type I inositol 1,4,5-trisphosphate receptor is reduced in streptozotocin-induced diabetic rats and mice

Intracellular Calcium Homeostasis and Kidney Disease

Kidney disease is a serious health problem that burdens our healthcare system. It is crucial to find the accurate pathogenesis of various types of kidney disease to provide guidance for precise therapies for patients suffering from these diseases. However, the exact molecular mechanisms underlying these diseases have not been fully understood. Disturbance of calcium homeostasis in renal cells plays a fundamental role in the development of various types of kidney disease, such as primary glomerular disease, diabetic nephropathy, acute kidney injury and polycystic kidney disease, through promoting cell proliferation, stimulating extracellular matrix accumulation, aggravating podocyte injury, disrupting cellular energetics as well as dysregulating cell survival and death dynamics. As a result, preventing the disturbance of calcium homeostasis in specific renal cells (such as tubular cells, podocytes and mesangial cells) is becoming one of the most promising therapeutic strategies in the treatment of kidney disease. The endoplasmic reticulum and mitochondria are two vital organelles in this process. Calcium ions cycle between the endoplasmic reticulum and mitochondria at the conjugation of these two organelles known as the mitochondria-associated endoplasmic reticulum membrane, maintaining calcium homeostasis. The pharmacologic modulation of cellular calcium homeostasis can be viewed as a novel therapeutic method for renal diseases. Here, we will introduce calcium homeostasis under physiological conditions and the disturbance of calcium homeostasis in kidney diseases. We will focus on the calcium homeostasis regulation in renal cells (including tubular cells, podocytes and mesangial cells), especially in the mitochondria- associated endoplasmic reticulum membranes of these renal cells.

A review of the role of inositols in conditions of insulin dysregulation and in uncomplicated and pathological pregnancy

Inositols, a group of 6-carbon polyols, are highly bioactive molecules derived from diet and endogenous synthesis. Inositols and their derivatives are involved in glucose and lipid metabolism and participate in insulin-signaling, with perturbations in inositol processing being associated with conditions involving insulin resistance, dysglycemia and dyslipidemia such as polycystic ovary syndrome and diabetes. Pregnancy is similarly characterized by substantial and complex changes in glycemic and lipidomic regulation as part of maternal adaptation and is also associated with physiological alterations in inositol processing. Disruptions in maternal adaptation are postulated to have a critical pathophysiological role in pregnancy complications such as gestational diabetes and pre-eclampsia. Inositol supplementation has shown promise as an intervention for the alleviation of symptoms in conditions of insulin resistance and for gestational diabetes prevention. However, the mechanisms behind these affects are not fully understood. In this review, we explore the role of inositols in conditions of insulin dysregulation and in pregnancy, and identify priority areas for research. We particularly examine the role and function of inositols within the maternal-placental-fetal axis in both uncomplicated and pathological pregnancies. We also discuss how inositols may mediate maternal-placental-fetal cross-talk, and regulate fetal growth and development, and suggest that inositols play a vital role in promoting healthy pregnancy.

Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles

Vascular tone of resistance arteries and arterioles determines peripheral vascular resistance, contributing to the regulation of blood pressure and blood flow to, and within the body's tissues and organs. Ion channels in the plasma membrane and endoplasmic reticulum of vascular smooth muscle cells (SMCs) in these blood vessels importantly contribute to the regulation of intracellular Ca2+ concentration, the primary determinant of SMC contractile activity and vascular tone. Ion channels provide the main source of activator Ca2+ that determines vascular tone, and strongly contribute to setting and regulating membrane potential, which, in turn, regulates the open-state-probability of voltage gated Ca2+ channels (VGCCs), the primary source of Ca2+ in resistance artery and arteriolar SMCs. Ion channel function is also modulated by vasoconstrictors and vasodilators, contributing to all aspects of the regulation of vascular tone. This review will focus on the physiology of VGCCs, voltage-gated K+ (KV) channels, large-conductance Ca2+-activated K+ (BKCa) channels, strong-inward-rectifier K+ (KIR) channels, ATP-sensitive K+ (KATP) channels, ryanodine receptors (RyRs), inositol 1,4,5-trisphosphate receptors (IP3Rs), and a variety of transient receptor potential (TRP) channels that contribute to pressure-induced myogenic tone in resistance arteries and arterioles, the modulation of the function of these ion channels by vasoconstrictors and vasodilators, their role in the functional regulation of tissue blood flow and their dysfunction in diseases such as hypertension, obesity, and diabetes. © 2017 American Physiological Society. Compr Physiol 7:485-581, 2017.

PKCα signaling pathway involves in TNF-α-induced IP3R1 expression in human mesangial cells

BACKGROUND

This study aimed to explore the effects of TNF-α on the expression of IP3R1 mRNA and protein in human mesangial cells (HMCs), and to elucidate the mechanism of TNF-α relating to IP3R1 expression in the occurrence of hepatorenal syndrome (HRS).

METHODS

HMCs were stimulated by tumor (TNF-α) with 100 ng/mL for different hours (2, 4, 8, and 24 hours). The expression changes of IP3R1 mRNA and protein were detected by quantitative real-time polymerase chain reaction and immunoblotting. Several inhibitors including D609, U73122, PP1, safingol, rottlerin and non-radioactive protein kinase C (PKC) were used to examine the mechanism of signal transduction of TNF-α-regulated IP3R1 in HMCs.

RESULTS

The levels of IP3R1 mRNA at 2 hours after TNF-α exposure were significantly enhanced and peaked at 8 hours in HMCs (P<0.01), then descended at 24 hours (P<0.01). The levels of IP3R1 protein at 4 hours after TNF-α exposure were obviously increased and peaked at 24 hours after TNF-α exposure (P<0.01). Compared to the control group, safingol (PKCα inhibitor) and D609 (phosphatidylcholine-specific phospholipase C inhibitor) significantly blocked the TNF-αinduced expression of IP3R1 mRNA (3.30±0.81 vs. 1.95±0.13, P<0.05; 2.10±0.49, P<0.01) and IP3R1 protein (3.09±0.13 vs. 1.86+0.39, P<0.01; 1.98±0.02, P<0.01). TNF-α promoted PKCα activation with maximal PKCα phosphorylation that occurred 8 hours after stimulation measured by non-radioactive PKC assay, and the effect was markedly attenuated by pretreatment with D609 or safingol.

CONCLUSION

TNF-α increased the expression of IP3R1 and this was mediated, at least in part, through the PC-PLC/PKCα signaling pathways in HMCs.

Calcium homeostasis in vascular smooth muscle cells is altered in type 2 diabetes by Bcl-2 protein modulation of InsP3R calcium release channels

This study examines the extent to which the antiapoptotic Bcl-2 proteins Bcl-2 and Bcl-x(L) contribute to diabetic Ca(2+) dysregulation and vessel contractility in vascular smooth muscle cells (VSMCs) through their interaction with inositol 1,4,5-trisphosphate receptor (InsP(3)R) intracellular Ca(2+) release channels. Measurements of intracellular ([Ca(2+)](i)) and sarcoplasmic reticulum ([Ca(2+)](SR)) calcium concentrations were made in primary cells isolated from diabetic (db/db) and nondiabetic (db/m) mice. In addition, [Ca(2+)](i) and constriction were recorded simultaneously in isolated intact arteries. Protein expression levels of Bcl-x(L) but not Bcl-2 were elevated in VSMCs isolated from db/db compared with db/m age-matched controls. In single cells, InsP(3)-evoked [Ca(2+)](i) signaling was enhanced in VSMCs from db/db mice compared with db/m. This was attributed to alterations in the intrinsic properties of the InsP(3)R itself because there were no differences between db/db and db/m in the steady-state [Ca(2+)](SR) or InsP(3)R expression levels. Moreover, in permeabilized cells the rate of InsP(3)R-dependent SR Ca(2+) release was increased in db/db compared with db/m VSMCs. The enhanced InsP(3)-dependent SR Ca(2+) release was attenuated by the Bcl-2 protein inhibitor ABT-737 only in diabetic cells. Application of ABT-737 similarly attenuated enhanced agonist-induced [Ca(2+)](i) signaling only in intact aortic and mesenteric db/db vessels. In contrast, ABT-737 had no effect on agonist-evoked contractility in either db/db or db/m vessels. Taken together, the data suggest that in type 2 diabetes the mechanism for [Ca(2+)](i) dysregulation in VSMCs involves Bcl-2 protein-dependent increases in InsP(3)R excitability and that dysregulated [Ca(2+)](i) signaling does not appear to contribute to increased vessel reactivity.

Endoplasmic-reticulum calcium depletion and disease

The endoplasmic reticulum (ER) as an intracellular Ca(2+) store not only sets up cytosolic Ca(2+) signals, but, among other functions, also assembles and folds newly synthesized proteins. Alterations in ER homeostasis, including severe Ca(2+) depletion, are an upstream event in the pathophysiology of many diseases. On the one hand, insufficient release of activator Ca(2+) may no longer sustain essential cell functions. On the other hand, loss of luminal Ca(2+) causes ER stress and activates an unfolded protein response, which, depending on the duration and severity of the stress, can reestablish normal ER function or lead to cell death. We will review these various diseases by mainly focusing on the mechanisms that cause ER Ca(2+) depletion.

Isoform-specific regulation of the inositol 1,4,5-trisphosphate receptor by O-linked glycosylation

The inositol 1,4,5-trisphosphate receptor (InsP(3)R), an intracellular calcium channel, has three isoforms with >65% sequence homology, yet the isoforms differ in their function and regulation by post-translational modifications. We showed previously that InsP(3)R-1 is functionally modified by O-linked β-N-acetylglucosamine glycosylation (O-GlcNAcylation) (Rengifo, J., Gibson, C. J., Winkler, E., Collin, T., and Ehrlich, B. E. (2007) J. Neurosci. 27, 13813-13821). We now report the effect of O-GlcNAcylation on InsP(3)R-2 and InsP(3)R-3. Analysis of AR4-2J cells, a rat pancreatoma cell line expressing predominantly InsP(3)R-2, showed no detectable O-GlcNAcylation of InsP(3)R-2 and no significant functional changes despite the presence of the enzymes for addition (O-β-N-acetylglucosaminyltransferase) and removal (O-β-N-acetylglucosaminidase) of the monosaccharide. In contrast, InsP(3)R-3 in Mz-ChA-1 cells, a human cholangiocarcinoma cell line expressing predominantly InsP(3)R-3, was functionally modified by O-GlcNAcylation. Interestingly, the functional impact of O-GlcNAcylation on the InsP(3)R-3 channel was opposite the effect measured with InsP(3)R-1. Addition of O-GlcNAc by O-β-N-acetylglucosaminyltransferase increased InsP(3)R-3 single channel open probability. Incubation of Mz-ChA-1 cells in hyperglycemic medium caused an increase in the InsP(3)-dependent calcium release from the endoplasmic reticulum. The dynamic and inducible nature of O-GlcNAcylation and the InsP(3)R isoform specificity suggest that this form of modification of InsP(3)R and subsequent changes in intracellular calcium transients are important in physiological and pathophysiological processes.

TNFα-induced IP3R1 expression through TNFR1/PC-PLC/PKCα and TNFR2 signalling pathways in human mesangial cell

BACKGROUND

Little information is available regarding the mechanisms involved in cytokine-induced type 1 inositol 1,4,5-trisphosphate receptor (IP(3)R1) expression in human mesangial cells (HMCs) in the occurrence of hepatorenal syndrome (HRS). Over-expression of IP(3)R1 would enhance both IP(3)-binding activity and sensitivity. We hypothesize that it is possible that increased IP(3)R1, induced by TNFα, would lead to increased IP(3) sensitivity in response to a variety of vasoconstrictors, and promote HMC contraction and thus lead to reduced GFP, promoting HRS occurrence and development.

METHODS

Quantitative real-time polymerase chain reaction and immunoblot assay were used to examine the effects of TNFα on IP(3)R1 mRNA and protein expression. Several inhibitors of kinases, depletion PKC, over-expression of dominant-negative mutant of PKC and non-radioactive PKC assay were used to examine the mechanism of signal transduction of TNFα-regulated IP(3)R1 in HMCs.

RESULTS

TNFα increased IP(3)R1 mRNA and protein expression in HMCs, an effect that was blocked by prolonged incubated chronic PMA, D609, safingol and also by transfection with domain-negative PKCα construct. TNFα activated and promoted autophosphorylation of the PKCα. In addition, both anti-TNFR1 and anti-TNFR2 antibodies blocked TNFα-induced IP(3)R1 protein expression, while only anti-TNFR1 antibodies but not anti-TNFR2 antibodies attenuated TNFα-induced PKCα activity.

CONCLUSIONS

TNFα increased the expression of IP(3)R1, and this was mediated, at least in part, through the TNFR1/PC-PLC/PKCα and TNFR2 signalling pathways in HMCs.

Roles of IP3R and RyR Ca2+ channels in endoplasmic reticulum stress and beta-cell death

OBJECTIVE

Endoplasmic reticulum (ER) stress has been implicated in the pathogenesis of diabetes, but the roles of specific ER Ca(2+) release channels in the ER stress-associated apoptosis pathway remain unknown. Here, we examined the effects of stimulating or inhibiting the ER-resident inositol trisphosphate receptors (IP(3)Rs) and the ryanodine receptors (RyRs) on the induction of beta-cell ER stress and apoptosis.

RESEARCH DESIGN AND METHODS

Kinetics of beta-cell death were tracked by imaging propidium iodide incorporation and caspase-3 activity in real time. ER stress and apoptosis were assessed by Western blot. Mitochondrial membrane potential was monitored by flow cytometry. Cytosolic Ca(2+) was imaged using fura-2, and genetically encoded fluorescence resonance energy transfer (FRET)-based probes were used to measure Ca(2+) in ER and mitochondria.

RESULTS

Neither RyR nor IP(3)R inhibition, alone or in combination, caused robust death within 24 h. In contrast, blocking sarco/endoplasmic reticulum ATPase (SERCA) pumps depleted ER Ca(2+) and induced marked phosphorylation of PKR-like ER kinase (PERK) and eukaryotic initiation factor-2alpha (eIF2alpha), C/EBP homologous protein (CHOP)-associated ER stress, caspase-3 activation, and death. Notably, ER stress following SERCA inhibition was attenuated by blocking IP(3)Rs and RyRs. Conversely, stimulation of ER Ca(2+) release channels accelerated thapsigargin-induced ER depletion and apoptosis. SERCA block also activated caspase-9 and induced perturbations of the mitochondrial membrane potential, resulting eventually in the loss of mitochondrial polarization.

CONCLUSIONS

This study demonstrates that the activity of ER Ca(2+) channels regulates the susceptibility of beta-cells to ER stress resulting from impaired SERCA function. Our results also suggest the involvement of mitochondria in beta-cell apoptosis associated with dysfunctional beta-cell ER Ca(2+) homeostasis and ER stress.

Uncoupling of ER-mitochondrial calcium communication by transforming growth factor-beta

Transforming growth factor-beta (TGF-beta) has been implicated as a key factor in mediating many cellular processes germane to disease pathogenesis, including diabetic vascular complications. TGF-beta alters cytosolic [Ca2+] ([Ca2+]c) signals, which in some cases may result from the downregulation of the IP3 receptor Ca2+ channels (IP3R). Ca2+ released by IP3Rs is effectively transferred from endoplasmic reticulum (ER) to the mitochondria to stimulate ATP production and to allow feedback control of the Ca2+ mobilization. To assess the effect of TGF-beta on the ER-mitochondrial Ca2+ transfer, we first studied the [Ca2+]c and mitochondrial matrix Ca2+ ([Ca2+]m) signals in single preglomerular afferent arteriolar smooth muscle cells (PGASMC). TGF-beta pretreatment (24 h) decreased both the [Ca2+]c and [Ca2+]m responses evoked by angiotensin II or endothelin. Strikingly, the [Ca2+]m signal was more depressed than the [Ca2+]c signal and was delayed. In permeabilized cells, TGF-beta pretreatment attenuated the rate but not the magnitude of the IP(3)-induced [Ca2+]c rise, yet caused massive depression of the [Ca2+]m responses. ER Ca2+ storage and mitochondrial uptake of added Ca2+ were not affected by TGF-beta. Also, TGF-beta had no effect on mitochondrial distribution and on the ER-mitochondrial contacts assessed by two-photon NAD(P)H imaging and electron microscopy. Downregulation of both IP3R1 and IP3R3 was found in TGF-beta-treated PGASMC. Thus, TGF-beta causes uncoupling of mitochondria from the ER Ca2+ release. The sole source of this would be suppression of the IP3R-mediated Ca2+ efflux, indicating that the ER-mitochondrial Ca2+ transfer depends on the maximal rate of Ca2+ release. The impaired ER-mitochondrial coupling may contribute to the vascular pathophysiology associated with TGF-beta production.

Thrombospondin-1 is an endogenous activator of TGF-beta in experimental diabetic nephropathy in vivo

OBJECTIVE

Transforming growth factor-beta (TGF-beta), the central cytokine responsible for the development of diabetic nephropathy, is usually secreted as a latent procytokine complex that has to be activated before it can bind to its receptors. Recent studies by our group demonstrated that thrombospondin-1 (TSP-1) is the major activator of latent TGF-beta in experimental glomerulonephritis in the rat, but its role in diabetic nephropathy in vivo is unknown.

RESEARCH DESIGN AND METHODS

Type 1 diabetes was induced in wild-type (n = 27) and TSP-1-deficient mice (n = 36) via streptozotocin injection, and diabetic nephropathy was investigated after 7, 9.5, and 20 weeks. Renal histology, TGF-beta activation, matrix accumulation, and inflammation were assessed by immunohistology. Expression of fibronectin and TGF-beta was evaluated using real-time PCR. Furthermore, functional parameters were examined.

RESULTS

In TSP-1-deficient compared with wild-type mice, the amount of active TGF-beta within glomeruli was significantly lower, as indicated by staining with specific antibodies against active TGF-beta or the TGF-beta signaling molecule phospho-smad2/3 or the typical TGF-beta target gene product plasminogen activator inhibitor-1. In contrast, the amount of glomerular total TGF-beta remained unchanged. The development of diabetic nephropathy was attenuated in TSP-1-deficient mice as demonstrated by a significant reduction of glomerulosclerosis, glomerular matrix accumulation, podocyte injury, renal infiltration with inflammatory cells, and renal functional parameters.

CONCLUSIONS

We conclude that TSP-1 is an important activator of TGF-beta in diabetic nephropathy in vivo. TSP-1-blocking therapies may be considered a promising future treatment option for diabetic nephropathy.

Role of fibrillin-1 in hypertensive and diabetic glomerular disease

The microfibrillar protein fibrillin-1 is a component of the mesangial matrix. Defects in fibrillin-1 predisposes individuals to vascular damage in Marfan syndrome, but the role of fibrillin-1 in kidney disease is unknown. We hypothesized that fibrillin-1 is involved in hypertensive or diabetic glomerular disease. DOCA-salt hypertension or streptozotocin (STZ) diabetes led to a significant increase in glomerular fibrillin-1 deposition. To test the functional role of fibrillin-1, DOCA hypertension and STZ diabetes were induced in mice homozygous for a mutation leading to a fivefold lower expression of fibrillin-1 (mgR/mgR). Untreated male mgR/mgR mice usually die from aortic dissection during the first 4 mo of life. All DOCA-treated mgR/mgR mice died within 2 wk after onset of DOCA treatment. DOCA-treated heterozygous (mgR/+) and their wild-type littermates displayed similar blood pressure levels, but albuminuria was significantly lower in mgR/+ than in wild-type mice after DOCA treatment. Similarly, STZ diabetic mgR/mgR and mgR/+ developed lower albuminuria than wild-type mice despite higher blood glucose levels in mgR/mgR and mgR/+ compared with wild-type mice. Blood pressure, blood glucose, and albuminuria did not differ among untreated mgR/mgR, mgR/+, and wild-type mice, respectively. In diabetic mgR/+ and mgR/mgR, but not in wild-type mice, an induction of glomerular decorin expression was observed. Thus underexpression of fibrillin-1 predisposes individuals to lethal aortic dissection in the presence of hypertension. On the other hand, albuminuria as a parameter of microvascular damage in hypertension and diabetes was ameliorated in fibrillin-1-underexpressing mice, possibly due to a compensatory upregulation of decorin. We conclude that fibrillin-1 may contribute to glomerular damage in hypertensive and diabetic kidney disease.

Involvement of transforming growth factor-beta in regulation of calcium transients in diabetic vascular smooth muscle cells

Altered calcium [Ca2+] transients of vascular smooth muscle cells to vasoconstrictors may contribute to altered regulation of blood flow in diabetes. We postulated that diabetes-induced transforming growth factor (TGF)-beta production contributes to impaired ANG II response of vascular smooth muscle cells in macrovessels and microvessels. Aortic vascular smooth muscle cells isolated from diabetic rats exhibited markedly impaired ANG II-induced cytosolic calcium [Ca2+] signal that was completely restored by pretreatment with anti-TGF-beta antibodies. Similar findings were noted in microvascular smooth muscle cells isolated from preglomerular vessels and cultured in high glucose. The impact of diabetes on [Ca2+] transients was replicated by addition of TGF-beta1 and -beta2 isoforms to aortic smooth muscle cells in culture and diabetic cells had enhanced production of TGF-beta2. In the in vivo condition, TGF-beta1 was increased in diabetic glomeruli, whereas TGF-beta2 was increased in diabetic aorta. The characteristic increase in glomerular filtration surface area found in diabetic rats was prevented by treatment with anti-TGF-beta antibodies, and impaired ANG II-induced aortic ring contraction in diabetic rats was completely restored by anti-TGF-beta antibodies. Impaired vascular dysfunction may be partly due to decreased inositol 1,4,5-trisphosphate receptor (IP3R), as reduced type I IP3R expression was found in diabetic aorta and restored by anti-TGF-beta antibodies. We conclude that TGF-beta plays an important role in the vascular dysfunction of early diabetes by inhibiting calcium transients in vascular smooth muscle cells.

TGF-beta-induced Ca(2+) influx involves the type III IP(3) receptor and regulates actin cytoskeleton

Ca(2+) influx has been postulated to modulate the signaling pathway of transforming growth factor-beta (TGF-beta); however, the underlying mechanism and functional significance of TGF-beta-induced stimulation of Ca(2+) influx are unclear. We show here that TGF-beta stimulates Ca(2+) influx in mesangial cells without Ca(2+) release. The influx of Ca(2+) is prevented by pharmacological inhibitors of inositol 1,4,5-trisphosphate receptors (IP(3)R) as well as specific antibodies to type III IP(3)R (IP(3)RIII) but not to type I IP(3)R (IP(3)RI). TGF-beta enhances plasma membrane localization of IP(3)RIII, whereas the sarcoplasmic-endoplasmic reticulum Ca(2+)-ATPase (SERCA) preferentially translocates to the nucleus. Untreated mesangial cells exhibit actin filamentous protrusions on the cell surface, and treatment with TGF-beta dramatically reduces this pattern. The alterations in the actin cytoskeleton by TGF-beta are dependent on TGF-beta-induced Ca(2+) influx. These studies identify a novel pathway by which TGF-beta regulates Ca(2+) influx and induces cytoskeletal alterations.

Endothelial-derived nitric oxide and angiotensinogen: blood pressure and metabolism during mouse pregnancy

The regulation of blood pressure during pregnancy involves several biological pathways. Candidate genes implicated in hypertensive diseases during pregnancy include those of the renin-angiotensin system and nitric oxide synthase (NOS). We evaluated blood pressure and metabolic characteristics during pregnancy in mutant mice. These included mice with a null mutation in the endothelial NOS (eNOS) gene (Nos3(-/-)), four copies of the angiotensinogen gene (Agt(2/2)), and mutations in both genes [four copies of Agt and heterozygous deficient for eNOS (Agt(2/2)Nos3(+/-)), four copies of Agt and homozygous deficient for eNOS (Agt(2/2)Nos3(-/-))]. Blood pressure measurements of nulliparous females from mutant strains were compared with two common laboratory strains C57Bl6/J and SV129 throughout their first pregnancy. Serum and urine analysis for the evaluation of renal and liver physiology were measured in the prepregnant state and during the third trimester of pregnancy. Throughout pregnancy blood pressures in all mutant strains were higher compared with controls. Agt(2/2)Nos3(-/-) showed the highest blood pressures and C57Bl6/J the lowest. Control mice, but not mutant mice, showed a second trimester decline in blood pressure. No immediate differences were noted regarding behavioral characteristics, renal or liver function parameters. Mice deficient for eNOS, mice with overexpression of Agt, and mice with mutations in both genes demonstrated higher blood pressure throughout pregnancy. There was no evidence of renal dysfunction, liver dysfunction, or hemolysis among any of the strains studied. We conclude that Nos3 and Agt are important genes in the regulation of blood pressure during pregnancy.

TGF-beta in diabetic kidney disease: role of novel signaling pathways

Diabetic nephropathy is the leading cause of end-stage renal disease in the United States and is a major contributing cause of morbidity and mortality in patients with diabetes. Despite conventional therapy to improve glycemic and blood pressure control the incidence of diabetic nephropathy is reaching epidemic proportions worldwide. As the major pathologic feature of diabetic nephropathy is diffuse mesangial matrix expansion, the pro-sclerotic cytokine transforming growth factor-beta, TGF-beta, is a leading candidate to mediate the progression of the disease. Numerous studies have now demonstrated that TGF-beta is a key factor in experimental models of diabetic kidney disease as well as in patients with diabetic nephropathy. Recent studies have begun to explore the mechanisms by which TGF-beta is stimulated by high glucose and how TGF-beta exerts its matrix-stimulating effects on renal cells. TGF-beta may also be involved in mediating the vascular dysfunction of diabetic kidney disease via its effects on the key intracellular calcium channel, the inositol trisphosphate receptor (IP(3)R). As there is substantial evidence for a cause and effect relationship between upregulation of TGF-beta and the progression of diabetic kidney disease, future studies will seek to establish specific targets along these pathways at which to intervene.