Involvement of Transglutaminase-2 in Pathological Changes in Renal Disease

The effect of TG2-inhibitory monoclonal antibody zampilimab on tissue fibrosis in human in vitro and primate in vivo models of chronic kidney disease

Fibrotic remodeling is the primary driver of functional loss in chronic kidney disease, with no specific anti-fibrotic agent available for clinical use. Transglutaminase 2 (TG2), a wound response enzyme that irreversibly crosslinks extracellular matrix proteins causing dysregulation of extracellular matrix turnover, is a well-characterized anti-fibrotic target in the kidney. We describe the humanization and characterization of two anti-TG2 monoclonal antibodies (zampilimab [hDC1/UCB7858] and BB7) that inhibit crosslinking by TG2 in human in vitro and rabbit/cynomolgus monkey in vivo models of chronic kidney disease. Determination of zampilimab half-maximal inhibitory concentration (IC50) against recombinant human TG2 was undertaken using the KxD assay and determination of dissociation constant (Kd) by surface plasmon resonance. Efficacy in vitro was established using a primary human renal epithelial cell model of tubulointerstitial fibrosis, to assess mature deposited extracellular matrix proteins. Proof of concept in vivo used a cynomolgus monkey unilateral ureteral obstruction model of chronic kidney disease. Zampilimab inhibited TG2 crosslinking transamidation activity with an IC50 of 0.25 nM and Kd of <50 pM. In cell culture, zampilimab inhibited extracellular TG2 activity (IC50 119 nM) and dramatically reduced transforming growth factor-β1-driven accumulation of multiple extracellular matrix proteins including collagens I, III, IV, V, and fibronectin. Intravenous administration of BB7 in rabbits resulted in a 68% reduction in fibrotic index at Day 25 post-unilateral ureteral obstruction. Weekly intravenous administration of zampilimab in cynomolgus monkeys with unilateral ureteral obstruction reduced fibrosis at 4 weeks by >50%, with no safety signals. Our data support the clinical investigation of zampilimab for the treatment of kidney fibrosis.

Decreased circulating transforming growth factor-beta (TGF-β) and kidney TGF-β immunoreactivity predict renal disease in cats with naturally occurring chronic kidney disease

OBJECTIVES

The aim of the present study was to compare the circulating transforming growth factor-beta (TGF-β) of clinically normal age-matched and naturally occurring chronic kidney disease (CKD) cats and to determine the correlation between the TGF-β expression and histopathological changes in cats with CKD.

METHODS

A total of 11 clinically normal age-matched and 27 cats with naturally occurring CKD were included in this study. Circulating TGF-β was quantified by immunoassays. Kaplan-Meier analysis was used to calculate the association between survival time and the concentration of circulating TGF-β. A general linear model was used to compare the circulating TGF-β between groups. Immunohistochemical analyses revealed TGF-β expression in renal tissues from cats with CKD that died during the study (n = 7) and in available archived renal tissue specimens taken at necropsy from cats that had previous CKD with renal lesions (n = 10). Correlations of the TGF-β expression and clinical parameters (n = 7) and histopathological changes (n = 17) were analysed using Spearman's rank correlation.

RESULTS

The median survival time of cats with a lower concentration of circulating TGF-β was shorter than that of cats with a higher concentration. The area under the curve of circulating TGF-β for predicting CKD was 0.781, indicating good differentiation. The study indicated a significant difference in circulating TGF-β concentrations between clinically normal cats and those with CKD and demonstrated that TGF-β expression is correlated with tubular atrophy.

CONCLUSIONS AND RELEVANCE

The study findings suggest that decreased serum TGF-β and tubular atrophy with TGF-β immunoreactivity may be significant in cats with CKD.

IgA nephropathy

IgA nephropathy (IgAN), the most prevalent primary glomerulonephritis worldwide, carries a considerable lifetime risk of kidney failure. Clinical manifestations of IgAN vary from asymptomatic with microscopic or intermittent macroscopic haematuria and stable kidney function to rapidly progressive glomerulonephritis. IgAN has been proposed to develop through a 'four-hit' process, commencing with overproduction and increased systemic presence of poorly O-glycosylated galactose-deficient IgA1 (Gd-IgA1), followed by recognition of Gd-IgA1 by antiglycan autoantibodies, aggregation of Gd-IgA1 and formation of polymeric IgA1 immune complexes and, lastly, deposition of these immune complexes in the glomerular mesangium, leading to kidney inflammation and scarring. IgAN can only be diagnosed by kidney biopsy. Extensive, optimized supportive care is the mainstay of therapy for patients with IgAN. For those at high risk of disease progression, the 2021 KDIGO Clinical Practice Guideline suggests considering a 6-month course of systemic corticosteroid therapy; however, the efficacy of systemic steroid treatment is under debate and serious adverse effects are common. Advances in understanding the pathophysiology of IgAN have led to clinical trials of novel targeted therapies with acceptable safety profiles, including SGLT2 inhibitors, endothelin receptor blockers, targeted-release budesonide, B cell proliferation and differentiation inhibitors, as well as blockade of complement components.

RhoA vesicle trafficking-mediated transglutaminase 2 membrane translocation promotes IgA1 mesangial deposition in IgA nephropathy

Transglutaminase 2 (TGase2) has been shown to contribute to the mesangial IgA1 deposition in a humanized mouse model of IgA nephropathy (IgAN), but the mechanism is not fully understood. In this study, we found that inhibition of TGase2 activity could dramatically decrease the amount of polymeric IgA1 (pIgA1) isolated from patients with IgAN that interacts with human mesangial cells (HMC). TGase2 was expressed both in the cytosol and on the membrane of HMC. Upon treatment with pIgA1, there were more TGase2 recruited to the membrane. Using a cell model of mesangial deposition of pIgA1, we identified 253 potential TGase2-associated proteins in the cytosolic fraction and observed a higher concentration of cellular vesicles and increased expression of Ras homolog family member A (RhoA) in HMC after pIgA1 stimulation. Both the amount of pIgA1 deposited on HMC and membrane TGase2 level were decreased by inhibition of the vesicle trafficking pathway. Mechanistically, TGase2 was found to be coprecipitated with RhoA in the cellular vesicles. Membrane TGase2 expression was greatly increased by overexpression of RhoA, while it was reduced by knockdown of RhoA. Our in vitro approach demonstrated that TGase2 was transported from the cytosol to the membrane through a RhoA-mediated vesicle-trafficking pathway that can facilitate pIgA1 interaction with mesangium in IgAN.

Current understanding of IgA antibodies in the pathogenesis of IgA nephropathy

Immunoglobulin A (IgA) is the most abundant isotype of antibodies, provides a first line of defense at mucosal surfaces against pathogens, and thereby contributes to mucosal homeostasis. IgA is generally considered as a non-inflammatory antibody because of its main function, neutralizing pathogenic virus or bacteria. Meanwhile, IgA can induce IgA-mediated diseases, such as IgA nephropathy (IgAN) and IgA vasculitis. IgAN is characterized by the deposition of IgA and complement C3, often with IgG and/or IgM, in the glomerular mesangial region, followed by mesangial cell proliferation and excessive synthesis of extracellular matrix in glomeruli. Almost half a century has passed since the first report of patients with IgAN; it remains debatable about the mechanism how IgA antibodies selectively bind to mesangial region-a hallmark of IgAN-and cause glomerular injuries in IgAN. Previous lectin- and mass-spectrometry-based analysis have revealed that IgAN patients showed elevated serum level of undergalactosylated IgA1 in O-linked glycans of its hinge region, called galactose-deficient IgA1 (Gd-IgA1). Thereafter, numerous studies have confirmed that the glomerular IgA from IgAN patients are enriched with Gd-IgA1; thus, the first hit of the current pathogenesis of IgAN has been considered to increase circulating levels of Gd-IgA1. Recent studies, however, demonstrated that this aberrant glycosylation alone is not sufficient to disease onset and progression, suggesting that several additional factors are required for the selective deposition of IgA in the mesangial region and induce nephritis. Herein, we discuss the current understanding of the characteristics of pathogenic IgA and its mechanism of inducing inflammation in IgAN.

Celiac Disease-Type Tissue Transglutaminase Autoantibody Deposits in Kidney Biopsies of Patients with IgA Nephropathy

An association between celiac disease and IgA nephropathy (IgAN) has been suggested. In celiac disease, in addition to circulating in serum, IgA-class tissue transglutaminase (tTG) autoantibodies are deposited in the small bowel mucosa and extraintestinal organs. In this case series of IgAN patients with or without celiac disease, we studied whether celiac disease-type IgA-tTG deposits occur in kidney biopsies. The study included nine IgAN patients, four of them with celiac disease. At the time of the diagnostic kidney biopsy serum tTG autoantibodies were measured and colocalization of IgA and tTG was investigated in the frozen kidney biopsies. Three IgAN patients with celiac disease had IgA-tTG deposits in the kidney even though in two of these the celiac disease diagnosis had been set years later. These deposits were not found in a patient with already diagnosed celiac disease following a gluten-free diet. Of the five non-celiac IgAN patients, three had IgA-tTG deposits in the kidney. We conclude that tTG-targeted IgA deposits can be found in the kidney biopsies of gluten-consuming IgAN patients but their specificity to celiac disease seems limited.

Transglutaminase 2 as a novel target in chronic kidney disease - Methods, mechanisms and pharmacological inhibition

Chronic kidney disease (CKD) is a global health problem with a prevalence of 10-15%. Progressive fibrosis of the renal tissue is a main feature of CKD, but current treatment strategies are relatively unspecific and delay, but do not prevent, CKD. Exploration of novel pharmacological targets to inhibit fibrosis development are therefore important. Transglutaminase 2 (TG2) is known to be central for extracellular collagenous matrix formation, but TG2 is a multifunctional enzyme and novel research has broadened our view on its extra- and intracellular actions. TG2 exists in two conformational states with different catalytic properties as determined by substrate availability and local calcium concentrations. The open conformation of TG2 depends on calcium and has transamidase activity, central for protein modification and cross-linking of extracellular protein components, while the closed conformation is a GTPase involved in transmembrane signaling processes. We first describe different methodologies to assess TG2 activity in renal tissue and cell cultures such as biotin cadaverine incorporation. Then we systematically review animal CKD models and preliminary studies in humans (with diabetic, IgA- and chronic allograft nephropathy) to reveal the role of TG2 in renal fibrosis. Mechanisms behind TG2 activation, TG2 externalization dependent on Syndecan-4 and interactions between TG and profibrotic molecules including transforming growth factor β and the angiotensin II receptor are discussed. Pharmacological TG2 inhibition shows antifibrotic effects in CKD. However, the translation of TG2 inhibition to treat CKD in patients is a challenge as clinical information is limited, and further studies on pharmacokinetics and efficacy of the individual compounds are required.

Aldosterone nongenomically induces angiotensin II receptor dimerization in rat kidney: role of mineralocorticoid receptor and NADPH oxidase

INTRODUCTION

Previous in vitro studies demonstrated that aldosterone nongenomically induces transglutaminase (TG) and reactive oxygen species (ROS), which enhanced angiotensin II receptor (ATR) dimerization. There are no in vivo data in the kidney.

MATERIAL AND METHODS

Male Wistar rats were intraperitoneally injected with normal saline solution, or aldosterone (Aldo: 150 μg/kg BW); or received pretreatment with eplerenone (mineralocorticoid receptor (MR) blocker, Ep. + Aldo), or with apocynin (nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor, Apo. + Aldo) 30 min before aldosterone. Thirty minutes after aldosterone injection, protein abundances of dimeric and monomeric forms of AT₁R and AT₂R, and protein abundances and localizations of TG2 and p47phox, a cytosolic subunit of NADPH oxidase, were determined by Western blot analysis and immunohistochemistry, respectively.

RESULTS

Protein abundances of dimeric forms of AT₁R and AT₂R were enhanced by 170% and 70%, respectively. Apocynin could block dimeric forms of both receptors while eplerenone inhibited only AT₂R. Monomeric protein levels of both receptors were maintained. Aldosterone significantly enhanced TG2 and p47phox protein abundances, which were blunted by eplerenone or apocynin. Aldosterone stimulated p47phox protein expression in both the cortex and the medulla while TG2 was induced mostly in the medulla. Eplerenone or apocynin normalized the immunoreactivity of both TG2 and p47phox.

CONCLUSIONS

This is the first in vivo study demonstrating that aldosterone nongenomically increases renal TG2 and p47phox protein expression and then activates AT₁R and AT₂R dimerizations. Aldosterone-stimulated AT₁R and AT₂R dimerizations are mediated through activation of NADPH oxidase. Aldosterone-induced AT₁R dimer formation is an MR-independent pathway, whereas the formation of AT₂R dimer is modulated in an MR-dependent manner.

Recent advances in the physiopathology of IgA nephropathy

Immunoglobulin A nephropathy or Berger's disease is the most common type of primary glomerulonephritis, which is characterized by IgA1-containing immune-deposits in the glomerular mesangium. Microscopic haematuria and proteinuria are the most common presentations. Mesangial cell proliferation with IgA deposition is found on renal biopsy. Mechanims of the disease implicate at least four key molecules have been implicated in immune complex formation: galactose-deficient IgA1, autoantibodies anti-galactose-deficient-IgA1, soluble CD89 (Fc receptor for IgA) and the CD71 mesangial IgA receptor (transferrin receptor). These factors associated with environmental factors (antigens, food and microbiota) are correlated with disease progression and recurrence after transplantation. This review exploits recent data on the role of these molecular players of the disease, which may improve future therapeutic management of immunoglobulin A nephropathy.

RTN1 mediates progression of kidney disease by inducing ER stress

Identification of new biomarkers and drug targets for chronic kidney disease (CKD) is required for the development of more effective therapy. Here we report an association between expression of reticulon 1 (RTN1) and severity of CKD. An isoform-specific increase in the expression of RTN1A is detected in the diseased kidneys from mice and humans, and correlates inversely with renal function in patients with diabetic nephropathy. RTN1 overexpression in renal cells induces ER stress and apoptosis, whereas RTN1 knockdown attenuates tunicamycin-induced and hyperglycaemia-induced ER stress and apoptosis. RTN1A interacts with PERK through its N-terminal and C-terminal domains, and mutation of these domains prevents this effect on ER stress. Knockdown of Rtn1a expression in vivo attenuates ER stress and renal fibrosis in mice with unilateral ureteral obstruction, and also attenuates ER stress, proteinuria, glomerular hypertrophy and mesangial expansion in diabetic mice. Together, these data indicate that RTN1A contributes to progression of kidney disease by inducing ER stress.

ER stress is associated with the pathogenesis of chronic kidney disease (CKD) and new CKD therapies are needed. Here the authors show that expression of Rtn1 can control severity of renal disease and that inhibition of its expression can attenuate ER stress and CKD.

Diagnosis and monitoring of IgA nephropathy: the role of biomarkers as an alternative to renal biopsy

IgA nephropathy (IgAN) is the most prevalent form of chronic glomerulonephritis in the world. The underlying pathogenesis of this autoimmune disease comprises the formation of immune complexes, including glycan-specific IgA1 or IgG antibodies and an aberrant glycosylation of IgA1. Until now, anatomopathological analysis of renal biopsies is essential for the diagnosis of IgAN and different histological classification systems have been proposed, e.g. the Oxford classification. However, a percutaneous renal biopsy is frequently not performed for several reasons and the Oxford classification system has some limitations. Since the poor prognosis of IgAN patients is partly the result of a delayed diagnosis, there is an urgent need for reliable noninvasive biomarkers that might be applicable in routine clinical practice. This article reviews the advances on the understanding of the underlying pathophysiological mechanisms of IgAN and discusses in depth the recent development of new biomarkers, including the use of proteomics and microRNAs.

Combined C4d and CD3 immunostaining predicts immunoglobulin (Ig)A nephropathy progression

A number of molecules have been shown recently to be involved in the pathogenesis and progression of immunoglobulin (Ig)A nephropathy (IgAN). Among these, we have selected C4d (complement lectin pathway involvement), CD3 (T cell marker, traducing interstitial inflammation), transglutaminase 2 (TGase-2, involved in tissue fibrosis development) and p-extracelluar-regulated kinase (ERK)1/2 (protein kinase intracellular signaling molecule) to perform a panel of immunohistological biomarkers and assess its predictive value for disease progression. Immunohistochemical staining of these biomarkers was performed in paraffin sections from 74 renal biopsy cases with the clinical diagnosis of IgAN. Association between score analysis of these parameters and disease course was assessed through univariate and multivariate analysis, including baseline clinical and histological data. Univariate analysis showed that glomerular C4d, tubulointerstitial TGase2 and CD3 scores were associated with baseline proteinuria and disease progression. Multivariate analysis showed that only baseline estimated glomerular filtration rate (eGFR), C4d and CD3 were associated independently with progressive kidney disease (decline of at least 50% in the eGFR or progression to end-stage renal disease (ESRD) during the follow-up period). Establishing an accurate prediction model for IgAN progression is still a matter of research in clinical nephrology. The complement system, particularly lectin pathway activation, and T cell activation, have been shown previously to be potential modifiers of the disease course. Here we show that the combination of two histological biomarkers (C4d and CD3) can be a powerful predictor of IgAN progression and a potential useful tool for the clinical approach of this disease.

[Formation of IgA deposits in Berger's disease: what we learned from animal models]

Immunoglobulin A (IgA) nephropathy (N) is the most common form of primary glomerulonephritis in the world and one of the first cause of end-stage renal failure. IgAN is characterized by the accumulation in mesangial areas of immune complexes containing IgA1. While epidemiology and clinical studies of IgAN are well-established, the mechanism(s) underlying disease development is poorly understood. The pathogenesis of this disease involves the deposition of polymeric and undergalactosylated IgA1 in the mesangium. Quantitative and structural changes of IgA1 play a key role in the development of the disease, due to functional abnormalities of two IgA receptors: the FcαR (CD89) expressed by blood myeloid cells and the transferrin receptor (TfR1) on mesangial cells. Abnormal IgA induces release of soluble CD89, responsible for the formation of circulating IgA complexes. These complexes are trapped by the TfR1 that is overexpressed on mesangial cells in IgAN patients, inducing the expression of transglutaminase 2. This enzyme stabilises IgA deposits at the surface of mesangial cells. These cells are then activated, proliferate and produce proinflammatory cytokines, leading to the loss of renal function.

Transglutaminase is essential for IgA nephropathy development acting through IgA receptors

Transglutaminase 2 is required for the development of IgA nephropathy.

IgA nephropathy (IgAN) is a common cause of renal failure worldwide. Treatment is limited because of a complex pathogenesis, including unknown factors favoring IgA1 deposition in the glomerular mesangium. IgA receptor abnormalities are implicated, including circulating IgA–soluble CD89 (sCD89) complexes and overexpression of the mesangial IgA1 receptor, TfR1 (transferrin receptor 1). Herein, we show that although mice expressing both human IgA1 and CD89 displayed circulating and mesangial deposits of IgA1–sCD89 complexes resulting in kidney inflammation, hematuria, and proteinuria, mice expressing IgA1 only displayed endocapillary IgA1 deposition but neither mesangial injury nor kidney dysfunction. sCD89 injection into IgA1-expressing mouse recipients induced mesangial IgA1 deposits. sCD89 was also detected in patient and mouse mesangium. IgA1 deposition involved a direct binding of sCD89 to mesangial TfR1 resulting in TfR1 up-regulation. sCD89–TfR1 interaction induced mesangial surface expression of TGase2 (transglutaminase 2), which in turn up-regulated TfR1 expression. In the absence of TGase2, IgA1–sCD89 deposits were dramatically impaired. These data reveal a cooperation between IgA1, sCD89, TfR1, and TGase2 on mesangial cells needed for disease development. They demonstrate that TGase2 is responsible for a pathogenic amplification loop facilitating IgA1–sCD89 deposition and mesangial cell activation, thus identifying TGase2 as a target for therapeutic intervention in this disease.

Tissue transglutaminase inhibits the TRPV5-dependent calcium transport in an N-glycosylation-dependent manner

Tissue transglutaminase (tTG) is a multifunctional Ca(2+)-dependent enzyme, catalyzing protein crosslinking. The transient receptor potential vanilloid (TRPV) family of cation channels was recently shown to contribute to the regulation of TG activities in keratinocytes and hence skin barrier formation. In kidney, where active transcellular Ca(2+) transport via TRPV5 predominates, the potential effect of tTG remains unknown. A multitude of factors regulate TRPV5, many secreted into the pro-urine and acting from the extracellular side. We detected tTG in mouse urine and in the apical medium of polarized cultures of rabbit connecting tubule and cortical collecting duct (CNT/CCD) cells. Extracellular application of tTG significantly reduced TRPV5 activity in human embryonic kidney cells transiently expressing the channel. Similarly, a strong inhibition of transepithelial Ca(2+) transport was observed after apical application of purified tTG to polarized rabbit CNT/CCD cells. Furthermore, tTG promoted the aggregation of the plasma membrane-associated fraction of TRPV5. Using patch clamp analysis, we observed a reduction in the pore diameter after tTG treatment, suggesting distinct structural changes in TRPV5 upon crosslinking by tTG. As N-linked glycosylation of TRPV5 is a key step in regulating channel function, we determined the effect of tTG in the N-glycosylation-deficient TRPV5 mutant. In the absence of N-linked glycosylation, TRPV5 was insensitive to tTG. Taken together, these observations imply that tTG is a novel extracellular enzyme inhibiting the activity of TRPV5. The inhibition of TRPV5 occurs in an N-glycosylation-dependent manner, signifying a common final pathway by which distinct extracellular factors regulate channel activity.

Transglutaminase 2 gene ablation protects against renal ischemic injury by blocking constant NF-κB activation

Transglutaminase 2 knockout (TGase2(-/-)) mice show significantly reduced inflammation with decreased myofibroblasts in a unilateral ureteral obstruction (UUO) model, but the mechanism remains to be clarified. Nuclear factor-κB (NF-κB) activation plays a major role in the progression of inflammation in an obstructive nephropathy model. However, the key factors extending the duration of NF-κB activation in UUO are not known. In several inflammatory diseases, we and others recently found that TGase 2 plays a key role in extending NF-κB activation, which contributes to the pathogenesis of disease. In the current study, we found that NF-κB activity in mouse embryogenic fibroblasts (MEFs) from TGase2(-/-) mice remained at the control level while the NF-κB activity of wild-type (WT) MEFs was highly increased under hypoxic stress. Using the obstructive nephropathy model, we found that NF-κB activity remained at the control level in TGase2(-/-) mouse kidney tissues, as measured by COX-2 expression, but was highly increased in WT tissues. We conclude that TGase 2 gene ablation reduces the duration of NF-κB activation in ischemic injury.

Tissue transglutaminase contributes to interstitial renal fibrosis by favoring accumulation of fibrillar collagen through TGF-beta activation and cell infiltration

Renal fibrosis is defined by the exaggerated accumulation of extracellular matrix proteins. Tissue transglutaminase (TG2) modifies the stability of extracellular matrix proteins and renders the extracellular matrix resistant to degradation. In addition, TG2 also activates transforming growth factor-beta (TGF-beta). We investigated the involvement of TG2 in the development of renal fibrosis using mice with a knockout of the TG2 gene (KO). These mice were studied at baseline and 12 days after unilateral ureteral obstruction, which induced a significant increase in interstitial TG2 expression in wild-type mice (P < 0.001). Interstitial fibrosis was evident in both groups, but total and fibrillar collagen was considerably lower in KO mice as compared with wild-type (P < 0.001). Similarly, mRNA and protein expression of collagen I were significantly lower in KO animals (P < 0.05). A statistically significant reduction in renal inflammation and fewer myofibroblasts were observed in KO mice (P < 0.01). Free active TGF-beta was decreased in KO mice (P < 0.05), although total (active + latent) TFG-beta concentration did not differ between groups. These results show that mice deficient in TG2 are protected against the development of fibrotic lesions in obstructive nephropathy. This protection results from reduced macrophage and myofibroblast infiltration, as well as from a decreased rate of collagen I synthesis because of decreased TGF-beta activation. Our results suggest that inhibition of TG2 may provide a new and important therapeutic target against the progression of renal fibrosis.

The protective role of uteroglobin through the modulation of tissue transglutaminase in the experimental crescentic glomerulonephritis

BACKGROUND AND METHODS

Tissue transglutaminase (tTG) may induce pro-inflammatory cytokines and produce irreversible end-products, thus promoting renal scarring. It has recently been confirmed that the crescent formation in murine experimental crescentic glomerulonephritis (ecGN) has been inhibited by the administration of recombinant uteroglobin (rUG). However, the ability of UG on tTG modulation has not been thoroughly assessed. In this study, we investigated the feasible protective role of UG in murine ecGN through the modulation of tTG and TGF-beta1 expressions. ecGN was induced by the administration of anti-GBM Ab into C57BL/6 mice.

RESULTS

Both proteinuria and BUN levels were distinctively lower in rUG-treated mice compared to those of disease control mice. Glomerular injuries such as mesangial proliferation, matrix production and crescent formation were lessened with the rUG treatment, and these findings were parallel with the attenuated expression of tTG and TGF-beta1. tTG and TGF-beta1 were expressed mainly on mesangial areas by the induction of ecGN and rUG treatment markedly attenuated the expressions of these proteins in glomeruli without spatial changes. With the addition of LPS to mesangial cells, the expressions of tTG and TGF-beta1 were up-regulated, whilst the addition of cysteamine, tTG inhibitor, attenuated the expression of tTG and TGF-beta1 as well as the cellular proliferation which was further induced by LPS.

CONCLUSION

We demonstrate for the first time that rUG is able to attenuate the renal injury through the modulation of expressions of tTG and TGF-beta1 in ecGN and further suggest a wide range of feasible molecular targets to reduce the severity of human glomerulonephritis.

Tissue transglutaminase expression and activity in normal and glaucomatous human trabecular meshwork cells and tissues

PURPOSE

Glaucoma is a leading cause of irreversible visual impairment and blindness in the world. A major risk factor for glaucoma is elevated intraocular pressure due to increased resistance of aqueous humor outflow through the trabecular meshwork (TM). In the glaucomatous TM, there is increased accumulation of extracellular matrix (ECM) material due to a disruption of the normal balance between ECM deposition and degradation. Tissue transglutaminase (TGM2) belongs to a family of calcium-dependent enzymes that catalyze the posttranslational modification of the ECM by cross-linking proteins, thus making these proteins resistant to enzymatic and physical degradation. It is possible that the increase in ECM proteins in the glaucomatous TM is due to increased cross-linking activity of TGM2. The purpose of this study was to determine whether there are differences in expression and activity of TGM2 between normal and glaucoma TM cells and tissues.

METHODS

Normal (n = 3 NTM) and glaucomatous (n = 3 GTM) human TM cell lines were grown until confluent. Western immunoblot analysis of cell lysates was used to compare TGM2 protein levels in NTM and GTM cells. TGM2 enzyme activity between NTM and GTM cells was studied by using a biotin cadaverine assay. In addition, immunohistochemistry of three normal and three glaucomatous TM tissues was used to evaluate the in vivo expression of TGM2, fibronectin (FN) and epsilon-(gamma-glutamyl) lysine (GGEL) proteins.

RESULTS

Western blot analysis and immunohistochemistry demonstrated the presence of TGM2 protein in both NTM and GTM cells. There was an increase in TGM2 protein in GTM cells compared with NTM cells, and GTM cells also had increased in TGM2 enzyme activity compared with NTM cells. Immunohistochemical results demonstrated increased expression of TGM2 and FN in GTM tissues. FN and GGEL proteins were colocalized in GTM tissues, indicating significant cross-linking of FN by TGM2.

CONCLUSIONS

This study demonstrated that both NTM and GTM cells express TGM2. In addition, TGM2 protein levels and enzyme activities were elevated in GTM cells. There was also an increase in colocalization of FN and GGEL protein in GTM tissues. These results indicate that TGM2 may play an important role in the pathogenesis of glaucoma by cross-linking ECM proteins such as FN and thus making the ECM more resistant to degradation.

Glucose metabolism, insulin resistance, and renal pathology in non-diabetic chronic kidney disease

BACKGROUND

The relation between insulin resistance and atherosclerosis is widely recognized, but it remains unknown whether glucose metabolism/insulin resistance is related to renal pathology in humans.

METHODS

We quantitatively evaluated pathological changes in the glomeruli, tubulointerstitium, and vessels in renal biopsy specimens from 23 patients with non-diabetic chronic kidney disease (CKD), all of whom took a 75-gram oral glucose tolerance test. We correlated the renal pathological changes with fasting plasma glucose (FPG), fasting plasma insulin, 2-hour plasma glucose (2-h PG), 2-hour plasma insulin (2-h PI), homeostasis model assessment of insulin resistance (HOMA-IR), and body mass index.

RESULTS

HOMA-IR exceeded 1.73 in 11 patients (47.8%), and 2-h PI exceeded 64.0 microU/ml in 14 (60.9%). FPG significantly correlated with interstitial fibrosis (r = 0.532, p = 0.009). The significance was marginal in the correlation between FPG and tubular atrophy and arterio-arteriolosclerosis. Statistically significant correlation was also found between 2-h PG and arterio-arteriolosclerosis (r = 0.422, p = 0.04) and between HOMA-IR and interstitial fibrosis (r = 0.416, p = 0.04).

CONCLUSION

Although precise mechanisms remain unknown, glucose metabolism/insulin resistance seem to play pathogenic roles in formation and progression of renal pathological changes, especially tubulointerstitial and vascular lesions, in non-diabetic CKD.