Dimethylarginine metabolism during acute and chronic rejection of rat renal allografts

Protein arginine methyltransferases in renal development, injury, repair, and fibrosis

Protein arginine methyltransferases (PRMTs) methylate a range of histone and non-histone substrates and participate in multiple biological processes by regulating gene transcription and post-translational modifications. To date, most studies on PRMTs have focused on their roles in tumors and in the physiological and pathological conditions of other organs. Emerging evidence indicates that PRMTs are expressed in the kidney and contribute to renal development, injury, repair, and fibrosis. In this review, we summarize the role and the mechanisms of PRMTs in regulating these renal processes and provide a perspective for future clinical applications.

Uremic Toxins, Oxidative Stress, Atherosclerosis in Chronic Kidney Disease, and Kidney Transplantation

Patients with chronic kidney disease (CKD) are at a high risk for cardiovascular disease (CVD), and approximately half of all deaths among patients with CKD are a direct result of CVD. The premature cardiovascular disease extends from mild to moderate CKD stages, and the severity of CVD and the risk of death increase with a decline in kidney function. Successful kidney transplantation significantly decreases the risk of death relative to long-term dialysis treatment; nevertheless, the prevalence of CVD remains high and is responsible for approximately 20-35% of mortality in renal transplant recipients. The prevalence of traditional and nontraditional risk factors for CVD is higher in patients with CKD and transplant recipients compared with the general population; however, it can only partly explain the highly increased cardiovascular burden in CKD patients. Nontraditional risk factors, unique to CKD patients, include proteinuria, disturbed calcium, and phosphate metabolism, anemia, fluid overload, and accumulation of uremic toxins. This accumulation of uremic toxins is associated with systemic alterations including inflammation and oxidative stress which are considered crucial in CKD progression and CKD-related CVD. Kidney transplantation can mitigate the impact of some of these nontraditional factors, but they typically persist to some degree following transplantation. Taking into consideration the scarcity of data on uremic waste products, oxidative stress, and their relation to atherosclerosis in renal transplantation, in the review, we discussed the impact of uremic toxins on vascular dysfunction in CKD patients and kidney transplant recipients. Special attention was paid to the role of native and transplanted kidney function.

The role of protein arginine methyltransferases in kidney diseases

The methylation of arginine residues by protein arginine methyltransferases (PRMTs) is a crucial post-translational modification for many biological processes, including DNA repair, RNA processing, and transduction of intra- and extracellular signaling. Previous studies have reported that PRMTs are extensively involved in various pathologic states, including cancer, inflammation, and oxidative stress reaction. However, the role of PRMTs has not been well described in kidney diseases. Recent studies have shown that aberrant function of PRMTs and its metabolic products-symmetric dimethylarginine (SDMA) and asymmetric dimethylarginine (ADMA)-are involved in several renal pathological processes, including renal fibrosis, acute kidney injury (AKI), diabetic nephropathy (DN), hypertension, graft rejection and renal tumors. We aim in this review to elucidate the possible roles of PRMTs in normal renal function and various kidney diseases.

Targeted metabolomic analysis of 33 amino acids and biogenic amines in human urine by ion-pairing HPLC-MS/MS: Biomarkers for tacrolimus nephrotoxicity after renal transplantation

Calcineurin inhibitor nephrotoxicity, especially for the widely used tacrolimus, has become a major concern in post-transplant immunosuppression. Multiparametric amino acid metabolomics is useful for biomarker identification of tacrolimus nephrotoxicity, for which specific quantitative methods are highlighted as a premise. This article presents a targeted metabolomic assay to quantify 33 amino acids and biogenic amines in human urine by high-performance liquid chromatography coupled with tandem mass spectrometry. Chromatographic separation was carried out on an Agilent Zorbax SB-C₁₈ column (3.0 × 150 mm, 5 μm) with addition of an ion-pairing agent in the mobile phase, and MS/MS detection was achieved in both the positive and negative multiple reaction monitoring modes. Good correlation coefficients (r² > 0.98) were obtained for most analytes. Intra- and inter-day precision, stability, carryover and incurred sample reanalysis met with the acceptance criteria of the guidance of the US Food and Drug Administration. Analysis on urine from healthy volunteers and renal transplantation patients with tacrolimus nephrotoxicity confirmed symmetric dimethylarginine and serine as biomarkers for kidney injury, with AUC values of 0.95 and 0.81 in receiver operating characteristic analysis, respectively. Additionally, symmetric dimethylarginine exhibited a tight correlation with serum creatinine, and was therefore indicative of renal function. The targeted metabolomic assay was time and cost prohibitive for amino acid analysis in human urine, facilitating the biomarker identification of tacrolimus nephrotoxicity.

FcγRIIb expression on B cells is associated with treatment efficacy for acute rejection after kidney transplantation

BACKGROUND

Fcγ receptors (FcγR) play a role in the acute rejection (AR) of organ transplants. FcγRIIB is an inhibitory FcγR expressed on B cells. Intravenous IgG (IVIG) and CD28 monoclonal antibody (mAb) have been shown to have immunomodulatory properties against AR.

AIM

To examine the association between FcγRIIB expression on B cell subpopulations and AR treatment efficacy.

METHODS

Male F344 rats were used as kidney donors and Lewis rats as recipients to establish models of renal transplantation. Rats were divided into five groups: sham, AR-PBS, AR-IVIG, AR-PNGase F-IVIG, and AR-CD28. Serum creatinine (Scr), blood urea nitrogen (BUN), and urine protein content were determined. Inflammatory markers were measured by ELISA, FcγR by western blotting, and spleen B cell activation by flow cytometry.

RESULTS

Scr, BUN, urinary protein content, levels of CRP, IL-10, TNF-α, IL-6, IL-8, and IgG were all increased in the AR-PBS group compared with the sham group (all P<0.01); these increases were partly reversed in the AR-IVIG, AR-PNGase F IVIG, and AR-CD28 groups (all P<0.01), with IVIG showing the better efficacy than PNGase F IVIG. Furthermore, blood and spleen FcγRIA and FcγRIIIA were increased by AR, while FcγRIIB expressions in splenic activated B cells and regulatory B cells were decreased; these changes were partly alleviated by all three treatments, with IVIG having the better effect than PNGase F IVIG.

CONCLUSION

We observed an association between B cell FcγRIIB expression and treatment efficacy for AR after kidney transplantation in rats.

Protein arginine methyltransferase 1 promoted the growth and migration of cancer cells in esophageal squamous cell carcinoma

Dysregulation of protein arginine methyltransferase 1 (PRMT1) has been reported in several cancer types. However, its expression pattern and biological functions in esophageal squamous cell carcinoma (ESCC) remained unknown. Here, we have found that the expression of PRMT1 was up-regulated in ESCC samples. In the biological function studies, forced expression of PRMT1 promoted the growth and migration of ESCC cells. However, knocking down the expression of PRMT1 inhibited the growth, migration, and metastasis of ESCC cells. Moreover, PRMT1 activated Hedgehog signaling and up-regulated the expression of target genes downstream of Hedgehog signaling. Taken together, our study revealed the oncogenic roles of PRMT1 in the progression of ESCC, and PRMT1 might be a promising therapeutic target for the treatment of ESCC.

Monocytic Tissue Transglutaminase in a Rat Model for Reversible Acute Rejection and Chronic Renal Allograft Injury

Acute rejection is a major risk factor for chronic allograft injury (CAI). Blood leukocytes interacting with allograft endothelial cells during acute rejection were suggested to contribute to the still enigmatic pathogenesis of CAI. We hypothesize that tissue transglutaminase (Tgm2), a multifunctional protein and established marker of M2 macrophages, is involved in acute and chronic graft rejection. We focus on leukocytes accumulating in blood vessels of rat renal allografts (Fischer-344 to Lewis), an established model for reversible acute rejection and CAI. Monocytes in graft blood vessels overexpress Tgm2 when acute rejection peaks on day 9 after transplantation. Concomitantly, caspase-3 is activated, suggesting that Tgm2 expression is linked to apoptosis. After resolution of acute rejection on day 42, leukocytic Tgm2 levels are lower and activated caspase-3 does not differ among isografts and allografts. Cystamine was applied for 4 weeks after transplantation to inhibit extracellular transglutaminase activity, which did, however, not reduce CAI in the long run. In conclusion, this is the first report on Tgm2 expression by monocytes in vivo. Tgm2 may be involved in leukocytic apoptosis and thus in reversion of acute rejection. However, our data do not support a role of extracellular transglutaminase activity as a factor triggering CAI during self-limiting acute rejection.

Expression of acetylcholine receptors by experimental rat renal allografts

Chronic allograft injury (CAI) is a major cause for renal allograft dysfunction and characterized by vasculopathies, tubular atrophy, and fibrosis. We demonstrated that numerous leukocytes interact with vascular endothelial cells of allografts and produce acetylcholine, which contributes to vascular remodeling. The cholinergic system might be a promising target for the development of novel therapies. However, neither the cellular mechanisms nor the acetylcholine receptors involved in CAI are known. Kidney transplantation was performed in the Lewis to Lewis and in the Fischer-334 to Lewis rat strain combination, which is an established experimental model for CAI. Expression of nicotinic and muscarinic acetylcholine receptors mRNA was quantified in renal tissue by real-time RT-PCR on days 9 and 42 after surgery. We detected CHRNA2-7, CHRNA10, CHRNB2, CHRNB4, and CHRM1-3 mRNA in normal kidneys and in renal transplants. In contrast, CHRNA9, CHRM4, and CHRM5 mRNA remained below the threshold of detection. In renal allografts, CHRNA3 and CHRNB4 mRNA expression were dramatically reduced compared to isografts. In conclusion, we demonstrated that most acetylcholine receptor subtypes are expressed by normal and transplanted kidneys. Allograft rejection downmodulates CHRNA3 and CHRNB4 mRNA. The role of different acetylcholine receptor subtypes in the development of CAI remains to be established.

Time course of asymmetric dimethylarginine and symmetric dimethylarginine levels after successful renal transplantation

BACKGROUND

Although renal transplantation (Tx) improves the outcome of patients with renal disease, cardiovascular (CV) risk remains high. Recently, it was demonstrated that asymmetric dimethylarginine (ADMA) levels predict CV events and graft survival in renal transplant recipients (RTRs). Little is known about the impact of renal Tx on the plasma levels of ADMA and symmetric dimethylarginine (SDMA). The present study aimed to define the time course of ADMA and SDMA after Tx.

METHODS

We prospectively followed 167 incident RTRs with visits at the time of Tx and 3 and 12 months thereafter. At all visits, demographics and relevant biochemistry were recorded and blood was sampled for analysis of ADMA and SDMA (high-performance liquid chromatography). Eighty-four patients had an additional sampling in the immediate postoperative period. In a case-controlled substudy (n = 31), we compared ADMA and SDMA levels between RTRs and chronic kidney disease (CKD) patients, matched for glomerular filtration rate, gender, age, CV history and diabetes.

RESULTS

Overall, plasma ADMA and SDMA levels decreased after Tx. The decline of SDMA was more pronounced and paralleled the recovery of renal function. Interestingly, the decline of ADMA was preceded by an increase in the immediate postoperative period. In the case-controlled substudy, SDMA levels were similar, whereas ADMA levels were significantly higher in RTRs compared with the CKD counterparts (P = 0.003).

CONCLUSION

ADMA levels follow a biphasic pattern after successful renal Tx with a transient rise in the immediate postoperative period followed by a decline. Levels remain elevated compared with CKD patients, matched for age, gender, diabetes, CV history and renal function.

Expression of nestin after renal transplantation in the rat

Chronic allograft injury (CAI) limits the long-term success of renal transplantation. Nestin is a marker of progenitor cells, which probably contribute to its pathogenesis. We hypothesize that nestin is induced by ischemia/reperfusion injury and acute rejection, main risk factors for CAI. Syngeneic renal transplantation was performed in Lewis rats and allogeneic transplantation in the Fischer 344 to Lewis strain combination, which results in reversible acute rejection and in CAI in the long-run. The Dark Agouti to Lewis rat strain combination was used to study fatal acute rejection. In untreated kidneys, nestin immunoreactivity was detected in glomeruli and in very few interstitial or microvascular cells. Syngeneic transplantation induced nestin expression within 4 days, which decreased until day 9 and returned to control levels on day 42. Nestin expression was strong during acute rejection and still detected during the pathogenesis of CAI on day 42. Nestin-positive cells were identified as endothelial cells and interstitial fibroblast-like cells co-expressing alpha-smooth muscle actin. A sub-population of them expressed proliferating cell nuclear antigen. In conclusion, nestin is induced in renal grafts by ischemia/reperfusion injury and acute rejection. It is expressed by proliferating myofibroblasts and endothelial cells and probably contributes to the pathogenesis of CAI.

Protein Arginine Methyltransferases (PRMTs): promising targets for the treatment of pulmonary disorders

Protein arginine methylation is a novel posttranslational modification that plays a pivotal role in a variety of intracellular events, such as signal transduction, protein-protein interaction and transcriptional regulation, either by the direct regulation of protein function or by metabolic products originating from protein arginine methylation that influence nitric oxide (NO)-dependent processes. A growing body of evidence suggests that both mechanisms are implicated in cardiovascular and pulmonary diseases. This review will present and discuss recent research on PRMTs and the methylation of non-histone proteins and its consequences for the pathogenesis of various lung disorders, including lung cancer, pulmonary fibrosis, pulmonary hypertension, chronic obstructive pulmonary disease and asthma. This article will also highlight novel directions for possible future investigations to evaluate the functional contribution of arginine methylation in lung homeostasis and disease.