Differential effects of rapamycin in anti-GBM glomerulonephritis

The Immunobiological Agents for Treatment of Antiglomerular Basement Membrane Disease

Combination therapy with glucocorticoids, cyclophosphamide, and plasmapheresis is recommended as the standard treatment for anti-glomerular basement membrane (anti-GBM) disease, but the prognosis of this disease remains poor. Several immunobiological agents have been administered or are expected to be useful for anti-GBM disease in light of refractory disease or the standard treatments' tolerability. Many data regarding the use of biologic agents for anti-GBM disease have accumulated, verifying the effectiveness and potential of biologic agents as a new treatment option for anti-GBM disease. Tumor necrosis factor (TNF) inhibitors were shown to be useful in animal studies, but these agents have no clinical use and were even shown to induce anti-GBM disease in several cases. Although the efficacy of the TNF-receptor antagonist has been observed in animal models, there are no published case reports of its clinical use. There are also no published reports of animal or clinical studies of anti-B-cell-activating factor, which is a member of the TNF family of agents. Anti-interleukin (IL)-6 antibodies have been demonstrated to have no effect on or to exacerbate nephritis in animal models. Anti-C5 inhibitor was observed to be useful in a few anti-GBM disease cases. Among the several immunobiological agents, only rituximab has been demonstrated to be useful in refractory or poor-tolerance patients or small uncontrolled studies. Rituximab is usually used in combination with steroids and plasma exchange and is used primarily as an alternative to cyclophosphamide, but there is insufficient evidence regarding the efficacy of rituximab for anti-GBM disease, and thus, randomized controlled studies are required.

Effect of Combined Mycophenolate and Rapamycin Treatment on Kidney Fibrosis in Murine Lupus Nephritis

Background: A significant proportion of lupus nephritis patients develop chronic kidney disease (CKD) and progressive kidney fibrosis, for which there is no specific treatment. We previously reported that mycophenolate or rapamycin monotherapy showed comparable efficacy in suppressing kidney fibrosis in a murine model of lupus nephritis through their direct action on mesangial cells. We extended our study to investigate the effect of combined mycophenolate and rapamycin treatment (MR) on kidney fibrosis in NZBWF1/J mice.

Methods: Female NZBWF1/J mice with active nephritis were randomized to receive vehicle or treatment with mycophenolate (50 mg/kg/day) and rapamycin (1.5 mg/kg/day) (MR) for up to 12 weeks, and the effect of treatment on clinical parameters, kidney histology, and fibrotic processes was investigated.

Results: Progression of nephritis in untreated mice was accompanied by mesangial proliferation, glomerulosclerosis, tubular atrophy, protein cast formation, increased mTOR and ERK phosphorylation, and induction of TGF-β1, IL-6, α-smooth muscle actin, fibronectin, and collagen expression. Combined MR treatment prolonged survival, improved kidney function, decreased anti-dsDNA antibody level, and ameliorated histopathological changes. The effect of combined MR treatment on kidney histology and function was comparable to that of mycophenolate or rapamycin monotherapy. In vitro studies in human mesangial cells showed that exogenous TGF-β1 and IL-6 both induced mTOR and ERK phosphorylation and downstream fibrotic processes. Both mycophenolic acid and rapamycin inhibited inflammatory and fibrotic processes induced by TGF-β1 or IL-6 by downregulating mTOR and ERK phosphorylation.

Conclusions: Our findings indicate that combined mycophenolate and rapamycin, at reduced dose, improves kidney fibrosis in murine lupus nephritis through their distinct effect on mTOR and ERK signaling in mesangial cells.

The p70S6K/PI3K/MAPK feedback loop releases the inhibition effect of high-dose rapamycin on rat mesangial cell proliferation

Glomerular mesangial cell (MC) proliferation is one of the causative factors of glomerular diseases and one of their prominent pathological features. Rapamycin can inhibit MC proliferation and slow the progression to chronic renal fibrosis. The present study was designed to observe the role of rapamycin in MC proliferation and to explore the mechanism by which rapamycin acts on Akt and MAPK/ERK1/2 pathways in mesangial cells. MTT assay and flow cytometry were used to evaluate the proliferation and the cell cycle phase of glomerular mesangial cells respectively. The mRNA expression level of p70S6K was detected by RT-qPCR. Western blotting was performed to determine p70S6K, PI3K/Akt, and PI3K/MAPK protein expression. We found that rapamycin could reduce mesangial cell proliferation and arrest the cell cycle in the G1 phase, however the inhibition effect of 1000 nmol/L rapamycin was not higher than that in the 100 nmol/L group. The results of western blotting showed that 1000 nmol/L rapamycin more significantly inhibited the phosphorylation of p70S6K than 100 nmol/L, suggesting there should be another signaling pathway that activates the proliferation of MCs. Moreover, our results revealed that 1000 nmol/L rapamycin led to Raf1-MEK1/2-ERK pathway activation through a p70S6K-PI3K-mediated feedback loop in MCs. This study demonstrated that high-dose rapamycin leads to ERK1/2 activation through a p70S6K/PI3K/MAPK feedback loop in rat MCs, thus reducing the inhibitory effect of rapamycin on MC proliferation.

Justicidin B Inhibits PDGF-BB-Induced Proliferation and ECM Accumulation in Mesangial Cells via Nrf2/HO-1 and Akt/mTOR Signaling Pathway

Mesangial proliferative glomerulonephritis (MsPGN) is characterized by mesangial cell proliferation, inflammation, and extracellular matrix deposition in the mesangial area, which develops into glomerulosclerosis and contributes to end-stage renal disease. Justicidin B is a bioactive compound isolated from Justicia procumbens L., a traditional herbal remedy that reduces proteinuria in nephritis. However, the mechanism of Justicidin B’s therapeutic effect on MsPGN remains unclear. This study was aimed to explore the positive effect of Justicidin B on MsPGN. The results showed that Justicidin B attenuated the proliferation induced by platelet-derived growth factor-BB (PDGF-BB) in MCs and blocked cell cycle progression. Likewise, inflammatory factors, including monocyte chemotactic protein 1 (MCP-1) and tumor necrosis factor alpha (TNF-α), in MCs were decreased after treatment with Justicidin B. In addition, Justicidin B exhibited antioxidant activity in PDGF-BB-induced MCs, shown by the decreased production of malondialdehyde and T-AOC, and increased the expression of superoxide dismutase. Besides, Justicidin B suppressed extracellular matrix (ECM) deposition by reducing the protein levels of collagen IV and fibronectin. Furthermore, we found that Justicidin B significantly inhibited activation of the Akt/mammalian target of rapamycin (mTOR) signaling pathway in MCs induced by PDGF-BB, but enhanced the levels of proteins in the nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase 1 (HO-1) pathway. Taken together, Justicidin B prevented PDGF-BB-induced proliferation, inflammation, oxidative stress, and ECM accumulation via regulating the activation of the Nrf2/HO-1 pathway and the Akt/mTOR signaling pathway.

Glucagon-Like Peptide-1 Receptor Agonism Improves Nephrotoxic Serum Nephritis by Inhibiting T-Cell Proliferation

Glucagon-like peptide (GLP)-1 analogs such as liraglutide improved albuminuria in patients with type 2 diabetes in large randomized controlled trials. One of the suspected mechanisms is the anti-inflammatory potential of GLP-1 receptor (Glp1r) agonism. Thus, the anti-inflammatory action of Glp1r agonism was tested in a nondiabetic, T-cell-mediated murine model of nephrotoxic serum nephritis (NTS). The role of Glp1r in NTS was evaluated by using Glp1r^-/- mice or C57BL/6 mice treated with liraglutide. In vitro, murine T cells were stimulated in the presence of liraglutide or vehicle. Glp1r^-/- mice displayed increased renal infiltration of neutrophils and T cells after induction of NTS. Splenocyte proliferation and TH1 cytokine transcription were increased in spleen and lymph nodes of Glp1r^-/- mice. Liraglutide treatment significantly improved the renal outcome of NTS in C57BL/6 mice by decreasing renal infiltration and proliferation of T cells, which resulted in decreased macrophage infiltration. In vitro, T cells stimulated in the presence of liraglutide showed decreased proliferation of TH1 and TH17 cells. Liraglutide blocked glycolysis in T cells and decreased their Glut1 mRNA expression. Together, Glp1r agonism protects mice from a T-cell-dependent glomerulonephritis model by inhibition of T-cell proliferation, possibly by interacting with their metabolic program. This mechanism may explain in part the renoprotective effects of Glp1r agonism in diabetic nephropathy.

mTOR-mediated podocyte hypertrophy regulates glomerular integrity in mice and humans

The cellular origins of glomerulosclerosis involve activation of parietal epithelial cells (PECs) and progressive podocyte depletion. While mammalian target of rapamycin-mediated (mTOR-mediated) podocyte hypertrophy is recognized as an important signaling pathway in the context of glomerular disease, the role of podocyte hypertrophy as a compensatory mechanism preventing PEC activation and glomerulosclerosis remains poorly understood. In this study, we show that glomerular mTOR and PEC activation-related genes were both upregulated and intercorrelated in biopsies from patients with focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy, suggesting both compensatory and pathological roles. Advanced morphometric analyses in murine and human tissues identified podocyte hypertrophy as a compensatory mechanism aiming to regulate glomerular functional integrity in response to somatic growth, podocyte depletion, and even glomerulosclerosis - all of this in the absence of detectable podocyte regeneration. In mice, pharmacological inhibition of mTOR signaling during acute podocyte loss impaired hypertrophy of remaining podocytes, resulting in unexpected albuminuria, PEC activation, and glomerulosclerosis. Exacerbated and persistent podocyte hypertrophy enabled a vicious cycle of podocyte loss and PEC activation, suggesting a limit to its beneficial effects. In summary, our data highlight a critical protective role of mTOR-mediated podocyte hypertrophy following podocyte loss in order to preserve glomerular integrity, preventing PEC activation and glomerulosclerosis.

Roles of mTOR complexes in the kidney: implications for renal disease and transplantation

The mTOR pathway has a central role in the regulation of cell metabolism, growth and proliferation. Studies involving selective gene targeting of mTOR complexes (mTORC1 and mTORC2) in renal cell populations and/or pharmacologic mTOR inhibition have revealed important roles of mTOR in podocyte homeostasis and tubular transport. Important advances have also been made in understanding the role of mTOR in renal injury, polycystic kidney disease and glomerular diseases, including diabetic nephropathy. Novel insights into the roles of mTORC1 and mTORC2 in the regulation of immune cell homeostasis and function are helping to improve understanding of the complex effects of mTOR targeting on immune responses, including those that impact both de novo renal disease and renal allograft outcomes. Extensive experience in clinical renal transplantation has resulted in successful conversion of patients from calcineurin inhibitors to mTOR inhibitors at various times post-transplantation, with excellent long-term graft function. Widespread use of this practice has, however, been limited owing to mTOR-inhibitor- related toxicities. Unique attributes of mTOR inhibitors include reduced rates of squamous cell carcinoma and cytomegalovirus infection compared to other regimens. As understanding of the mechanisms by which mTORC1 and mTORC2 drive the pathogenesis of renal disease progresses, clinical studies of mTOR pathway targeting will enable testing of evolving hypotheses.

The Akt/mTOR/p70S6K pathway is activated in IgA nephropathy and rapamycin may represent a viable treatment option

IgA nephropathy (IgAN) is one of the most frequent forms of glomerulonephritis, and 20 to 40% of patients progress to end-stage renal disease (ESRD) within 20 years of disease onset. However, little is known about the molecular pathways involved in the altered physiology of mesangial cells during IgAN progression. This study was designed to explore the role of mTOR signaling and the potential of targeted rapamycin therapy in a rat model of IgAN. After establishing an IgA nephropathy model, the rats were randomly divided into four groups: control, control+rapamycin, IgAN and IgA+rapamycin. Western blotting and immunohistochemistry were performed to determine phospho-Akt, p70S6K and S6 protein levels. Coomassie Brilliant Blue was utilized to measure 24-h urinary protein levels. The biochemical parameters of the rats were analyzed with an autoanalyzer. To evaluate IgA deposition in the glomeruli, FITC-conjugated goat anti-rat IgA antibody was used for direct immunofluorescence. Cellular proliferation and the mesangial matrix in glomeruli were assayed via histological and morphometric procedures. Our results showed that p70S6K, S6 and Akt phosphorylation were significantly upregulated in IgAN rats, and rapamycin effectively inhibited p70S6K and S6 phosphorylation. A low dose of the mTOR inhibitor rapamycin reduced proteinuria, inhibited IgA deposition, and protected kidney function in an IgAN rat model. Low-dose rapamycin treatment corresponded to significantly lower cellular proliferation rates and a decreased mesangial matrix in the glomeruli. In conclusion, the Akt/mTOR/p70S6K pathway was activated in IgAN, and our findings suggested that rapamycin may represent a viable option for the treatment of IgAN.

Induction monotherapy with sirolimus has selected beneficial effects on glomerular and tubulointersititial injury in nephrotoxic serum nephritis

Background

The study aimed to test the hypothesis that therapeutic treatment with a mammalian target of rapamycin complex 1 inhibitor reduces renal cell proliferation and attenuates glomerular and tubulointerstitial injury in the early phase of nephrotoxic serum nephritis (NSN) in rats.

Methods

Male Wistar-Kyoto rats received a single tail-vein injection of sheep anti-rat glomerular basement membrane serum (day 0) and were treated with vehicle or sirolimus (0.25 mg/kg/day by subcutaneous injection) from day 1 until day 14.

Results

Treatment with sirolimus attenuated kidney enlargement by 41% (P<0.05), improved endogenous creatinine clearance by 50% (P<0.05), and reduced glomerular and tubulointerstitial cell proliferation by 53% and 70%, respectively, (P<0.05 compared to vehicle) in rats with NSN. In glomeruli, sirolimus reduced segmental fibrinoid necrosis by 69%, autologous rat immunoglobulin G deposition, glomerular capillary tuft enlargement, and periglomerular myofibroblast (α-smooth muscle actin-positive cells) accumulation (all P<0.05) but did not significantly affect glomerular crescent formation (P=0.15), macrophage accumulation (P=0.25), or the progression of proteinuria. In contrast, sirolimus preserved tubulointerstitial structure and attenuated all markers of injury (interstitial ED-1- and α-smooth muscle actin-positive cells and tubular vimentin expression; all P<0.05). By immunohistochemistry and Western blot analysis, sirolimus reduced the glomerular and tubulointerstitial expression of phosphorylated (Ser 235/236) S6-ribosomal protein (P<0.05).

Conclusion

Induction monotherapy with sirolimus suppressed target of rapamycin complex 1 activation, renal cell proliferation, and injury during the early stages of rodent NSN, but the degree of histological protection was more consistent in the tubulointerstitium than the glomerular compartment.

Rapamycin slows IgA nephropathy progression in the rat

BACKGROUND

IgA nephropathy (IgAN) is the most frequent glomerulonephritis worldwide. Different therapeutic approaches have been tested against IgAN. The present study was designed to explore the renoprotective potential of low-dose mammalian target of rapamycin (mTOR) inhibitor rapamycin in an IgAN rat model and the possible mechanism of action.

METHODS

After establishing an IgAN model, the rats were randomly divided into four groups: control, control with rapamycin treatment, IgAN model, and IgAN model with rapamycin treatment. Coomassie Brilliant Blue was utilized to measure 24-hour urinary protein levels. Hepatic and renal function was determined with an autoanalyzer. Proliferation was assayed via 5-bromo-2'-deoxyuridine incorporation. Real-time PCR and immunohistochemistry were utilized to detect the expression of α-SMA, collagen I, collagen III, TGF-β1 and platelet-derived growth factor. Western blotting and immunohistochemistry were performed to determine p-S6 protein levels.

RESULTS

Low-dose mTOR inhibitor rapamycin prevented an additional increase in proteinuria and protected kidney function in a model of IgAN. Rapamycin directly or indirectly interfered with multiple key pathways in the progression of IgAN to end-stage renal disease: (1) reduced the deposition of IgA and inhibited cell proliferation; (2) decreased the expression of fibrosis markers α-SMA and type III collagen, and (3) downregulated the expression of the profibrotic growth factors platelet-derived growth factor and TGF-β1. The expression of p-S6 was significantly elevated in IgAN rats.

CONCLUSIONS

The mTOR pathway was activated in IgAN rats and the early application of low-dose mTOR inhibitor rapamycin may slow the renal injury of IgAN in rats.

The mTOR-inhibitor rapamycin mediates proteinuria in nephrotoxic serum nephritis by activating the innate immune response

Rapamycin (Rapa) is an immunosuppressant used to prevent rejection in recipients of renal transplants. Its clinical use is limited by de novo onset or exacerbation of preexisting proteinuria. In the present study, Rapa administration was started 14 days after induction of murine nephrotoxic serum nephritis (NTS) to study glomerular effects of this mammalian target of rapamycin (mTOR) inhibitor. Glomeruli were laser-microdissected, and real-time PCR was performed to assess effects on glomerular cells and the expression of inflammatory cytokines. Immunohistochemical stainings were performed to confirm mRNA data on the protein level. Compared with nephritic control animals, Rapa-treated mice developed significantly increased albuminuria. This was accompanied by a more prominent glomerular infiltration by CD4(+) T cells and macrophages. Glomerular mRNA expression profiling revealed increased levels of the proinflammatory cytokines interleukin-6 and tumor necrosis factor-α, and the chemokines monocyte chemoattractant protein-1 and macrophage inflammatory protein-1β and their cognate macrophage-associated receptors CCR2 and CCR5 in the Rapa-treated animals. Furthermore, there were elevated glomerular transcription levels of the regulatory T cell phenotype transcription factor Foxp3. No differences in the glomerular expression of the podocyte marker nephrin or the endothelial cell marker CD31 were observed on the mRNA or protein level. In conclusion, our data indicate that Rapa-induced proteinuria in NTS is a result of the activation of the innate immune system rather than a direct toxicity to podocytes or glomerular endothelial cells.

Rapamycin induced ultrastructural and molecular alterations in glomerular podocytes in healthy mice

BACKGROUND

In the normal kidney, rapamycin is considered to be non-nephrotoxic. In the present study, we investigated whether rapamycin is indeed non-nephrotoxic by examining the ultrastructural and molecular alterations of podocytes in healthy mice.

METHODS

Balb/c mice were given three different intraperitoneal doses of rapamycin for 1 week (dose model)-low-dose group: 1 mg/kg/day, intermediate-dose (ID) group: 1.5 mg/kg/day and high-dose (HD) group: 3 mg/kg/day; four mice in each group. An ID of rapamycin was also given for three different periods (time model): 1, 4 and 8 weeks; four mice were in each group. Mice treated with dimethyl sulphoxide served as controls. Body weight was measured weekly. Renal function was assessed by serum creatinine at the time of sacrifice. For estimation of albuminuria, 24-h urine collections were performed before treatment and weekly thereafter. Glomerular content of nephrin, podocin, Akt and Ser473-phospho-Akt was estimated by western blot and immunofluorescence. Nephrin and podocin messenger RNA (mRNA) were measured by real-time polymerase chain reaction. Mean podocyte foot process width (FPW) was measured by electron microscopy.

RESULTS

Urine albumin levels increased in the HD and 4-week groups. Renal function was modestly deteriorated in the HD group. The mean FPW increased in a dose-dependant manner at Week 1, further deteriorated at Week 4 and finally improved at Week 8. Nephrin and podocin mRNA levels showed a significant decrease at Week 1 and were restored at Week 4 and 8. Nephrin and podocin protein levels were reduced at Week 4 and recovered at Week 8. Ser473-phospho-Akt significantly increased in all rapamycin-treated groups.

CONCLUSIONS

Rapamycin induced significant ultrastructural and molecular alterations in podocytes in association with albuminuria. These alterations happened early during treatment and they tended to improve over an 8-week treatment period.

Treatment with a cyclin-dependent kinase inhibitor, seliciclib, is effective in reducing glomerular macrophage numbers and the severity of established experimental glomerulonephritis

AIM

The cyclin-dependent kinase inhibitor, seliciclib (R-roscovitine, CYC202), has anti-proliferative activity through its inhibition of cyclin-dependent kinase 2. We hypothesized that treatment with seliciclib would reduce glomerular macrophage numbers and glomerular crescent formation in experimental crescentic glomerulonephritis even when treatment is started after onset of disease.

METHOD

Nephrotoxic nephritis (NTN) was induced in Wistar Kyoto rats. In experiment 1, seliciclib (150 mg/kg per day) was given by oral gavage from 1 h before induction of NTN and continued to day 14. In experiment 2, treatment was started on day 4 of NTN and continued to day 14 in order to examine the effect of seliciclib in established glomerulonephritis.

RESULTS

In experiment 1, seliciclib reduced proteinuria (119.5 ± 13.9 vs 191.4 ± 18.8 mg/day, P < 0.01), serum creatinine (54.0 ± 3.0 vs 81.0 ± 2.5 µmol/L, P < 0.005) and glomerular crescent score (23.9 ± 2.1 vs 44.6 ± 2.2, P < 0.005) in comparison with controls. In experiment 2, seliciclib ameliorated established glomerulonephritis, with reduction in proteinuria (58 ± 16 vs 165 ± 13 mg/day, P < 0.005), serum creatinine (39 ± 3 vs 62 ± 5 µmol/L, P < 0.05), glomerular macrophage numbers (6.8 ± 2.5 vs 18.5 ± 1.2 ED1+ cells per glomerular cross section, P < 0.05), glomerular cell proliferation (1.2 ± 0.37 vs 4.2 ± 0.80 bromodeoxyuridine (BrdU)+ cells per glomerular section, P < 0.05) and crescent score (10.8 ± 1.6 vs 43.9 ± 1.4, P < 0.05), in comparison with the controls.

CONCLUSION

Seliciclib is effective in both prevention and treatment of established crescentic glomerulonephritis in Wistar Kyoto rats, in association with a reduction in the number of glomerular macrophages. We suggest that seliciclib, or other cyclin-dependent kinase inhibitors, may represent a novel therapeutic approach for patients with proliferative glomerulonephritis.

Role of amino acid transporter LAT2 in the activation of mTORC1 pathway and the pathogenesis of crescentic glomerulonephritis

Molecular mechanisms and signaling pathways leading to cellular proliferation and lesion formation in the crescentic glomerulonephritis (CGN) remain elusive. In the present study we have explored a potential role of the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway and amino acid transporter (LAT) in the pathogenesis of CGN. Immunohistochemistry and western blot analysis of glomeruli isolated from a rat model of CGN revealed that activation of mTORC1 preceded crescent formation in glomerular parietal epithelial cells (PECs) and podocytes. Daily treatment of rats with the mTOR inhibitor everolimus just after induction of CGN was not beneficial and instead led to increased cellular necrosis of PECs. However, daily treatment starting 7 days after the onset of CGN was beneficial and maintained intact glomeruli. Out of three forms of L-type neutral amino acid transporters (LAT1-LAT3) studied here, only LAT2 was found to be upregulated in the PECs and podocytes in advance of the crescent formation as well as in the crescent lesion itself. Cell culture study revealed that plasma membrane expression of LAT2 markedly stimulated mTORC1 signaling pathway, which was significantly abrogated by coexistence of LAT inhibitor. Finally, LAT inhibitor significantly abrogated development of crescent formation of CGN on day 7. Our data suggest that LAT2 may have a pivotal role in the pathogenesis of CGN by activating the mTORC1 pathway in the glomerular epithelial cells.

IL-9 production by regulatory T cells recruits mast cells that are essential for regulatory T cell-induced immune suppression

Both mast cells (MCs) and regulatory T cells (Tregs) have gained attention as immunosuppressive cell populations. To investigate a possible interaction, we used the Th1- and Th17-dependent model of nephrotoxic serum nephritis (NTS), in which both MCs and Tregs have been shown to play a protective role. Transfer of wild-type (wt) Tregs into wt recipients almost completely prevents development of NTS and leads to a profound increase of MCs in the renal draining lymph nodes (LNs). By contrast, transfer of wt Tregs into animals deficient in MCs, which are characterized by an exaggerated susceptibility to NTS, no longer exhibited protective effects. Blocking the pleiotropic cytokine IL-9, known to be involved in MC recruitment and proliferation, by means of a mAb in mice receiving Tregs abrogated protection from NTS. Moreover, transfer of IL-9-deficient Tregs also failed to protect from NTS. In the absence of Treg-derived IL-9, MCs fail to accumulate in the LNs, despite the fact that IL-9 deficiency does not alter the general suppressive activity of Tregs. In summary, to our knowledge, we provide the first direct in vivo evidence that the nephroprotective, anti-inflammatory effects of Tregs critically depend on IL-9-mediated attraction of MCs into kidney-draining LNs.

Prospects for mTOR inhibitor use in patients with polycystic kidney disease and hamartomatous diseases

Mammalian target of rapamycin (mTOR) is the core component of two complexes, mTORC1 and mTORC2. mTORC1 is inhibited by rapamycin and analogues. mTORC2 is impeded only in some cell types by prolonged exposure to these compounds. mTOR activation is linked to tubular cell proliferation in animal models and human autosomal dominant polycystic kidney disease (ADPKD). mTOR inhibitors impede cell proliferation and cyst growth in polycystic kidney disease (PKD) models. After renal transplantation, two small retrospective studies suggested that mTOR was more effective than calcineurin inhibitor-based immunosuppression in limiting kidney and/or liver enlargement. By inhibiting vascular remodeling, angiogenesis, and fibrogenesis, mTOR inhibitors may attenuate nephroangiosclerosis, cyst growth, and interstitial fibrosis. Thus, they may benefit ADPKD at multiple levels. However, mTOR inhibition is not without risks and side effects, mostly dose-dependent. Under certain conditions, mTOR inhibition interferes with adaptive increases in renal proliferation necessary for recovery from injury. They restrict Akt activation, nitric oxide synthesis, and endothelial cell survival (downstream from mTORC2) and potentially increase the risk for glomerular and peritubular capillary loss, vasospasm, and hypertension. They impair podocyte integrity pathways and may predispose to glomerular injury. Administration of mTOR inhibitors is discontinued because of side effects in up to 40% of transplant recipients. Currently, treatment with mTOR inhibitors should not be recommended to treat ADPKD. Results of ongoing studies must be awaited and patients informed accordingly. If effective, lower dosages than those used to prevent rejection would minimize side effects. Combination therapy with other effective drugs could improve tolerability and results.

Tim3 is upregulated and protective in nephrotoxic serum nephritis

T cell immunoglobulin and mucin protein-3 (Tim3) is mainly expressed on the cell surface of T-helper lymphocytes (T(H)) that negatively regulates T(H)-type 1 (T(H)-1) responses. Because blockade of Tim3 aggravates disease activity in T(H)-1-dependent diseases, we investigated whether Tim3 is involved in the pathogenesis of the T(H)-1-dependent nephrotoxic nephritis (NTS). We first evaluated Tim3 expression in mice after induction of nephrotoxic serum nephritis (NTS) and then studied the effects of anti-Tim3 treatment toward the course of NTS for up to seven days. Whereas Tim3 expression was undetectable in control mice, we found significantly increased Tim3 expression in kidneys, but not in draining lymph nodes, at one, four, and eight weeks after induction of NTS. Tim3-expressing cells that infiltrated kidneys of mice subjected to NTS turned out to be CD4(+) T cells rather than CD8(+) cytotoxic T cells and dendritic cells. Administration of a blocking anti-Tim3 antibody aggravated nephritis as shown by significantly increased albuminuria, respective histological changes, and increased expression of the kidney injury molecule lipocalin-2. In parallel, an increase of infiltrating T cells, macrophages, and macrophage pro-inflammatory cytokine formation as well as increased proliferation and apoptosis in kidneys of anti-Tim3-treated mice was detected. Together, we provide the first evidence that Tim3 is up-regulated in kidneys in NTS and that Tim3 exerts protective roles in the course of disease.

Epigallocatechin-3-gallate (EGCG) attenuates inflammation in MRL/lpr mouse mesangial cells

Epigallocatechin-3-gallate (EGCG), a bioactive component of green tea, has been reported to exert anti-inflammatory effects on immune cells. EGCG is also shown to activate the metabolic regulator, adenosine 5'-monophosphate-activated protein kinase (AMPK). Reports have also indicated that EGCG inhibits the immune-stimulated phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway. The PI3K/Akt/mTOR pathway has been implicated in mesangial cell activation in lupus. Mesangial cells from MRL/lpr lupus-like mice are hyper-responsive to immune stimulation and overproduce nitric oxide (NO) and other inflammatory mediators when stimulated. In our current studies, we sought to determine the mechanism by which EGCG attenuates immune-induced expression of pro-inflammatory mediators. Cultured mesangial cells from MRL/lpr mice were pre-treated with various concentrations of EGCG and stimulated with lipopolysaccharide (LPS)/interferon (IFN)-gamma. EGCG activated AMPK and blocked LPS/IFN-gamma-induced inflammatory mediator production (iNOS expression, supernatant NO and interleukin-6). Interestingly, EGCG attenuated inflammation during AMPK inhibition indicating that the anti-inflammatory effect of EGCG may be partially independent of AMPK activation. Furthermore, we found that EGCG effectively inhibited the immune-stimulated PI3K/Akt/mTOR pathway independently of AMPK, by decreasing phosphorylation of Akt, suggesting an alternate mechanism for EGCG-mediated anti-inflammatory action in mesangial cells. Taken together, these studies show that EGCG attenuated inflammation in MRL/lpr mouse mesangial cells via the PI3K/Akt/mTOR pathway. Our findings suggest a potential therapeutic role for the use of EGCG to regulate inflammation and control autoimmune disease.

The multifunctional role of mTOR in innate immunity: implications for transplant immunity

The mammalian target of rapamycin (mTOR) is an evolutionary conserved serine-threonine kinase that senses various environmental stimuli in most cells primarily to control cell growth. Restriction of cellular proliferation by mTOR inhibition led to the use of mTOR inhibitors as immunosuppressants in allogeneic transplantation as well as novel anticancer agents. However, distinct inflammatory side effects such as fever, pneumonitis, glomerulonephritis or anemia of chronic disease have been observed under this treatment regime. Apart from the mere cell-cycle regulatory effect of mTOR in dividing cells, recent data revealed a master regulatory role of mTOR in the innate immune system. Hence, inhibition of mTOR promotes proinflammatory cytokines such as IL-12 and IL-1beta, inhibits the anti-inflammatory cytokine IL-10 and boosts MHC antigen presentation via autophagy in monocytes/macrophages and dendritic cells. Moreover, mTOR regulates type I interferon production and the expression of chemokine receptors and costimulatory molecules. These results place mTOR in a complex immunoregulatory context by controlling innate and adaptive immune responses. In this review, we discuss the clinical consequences of mTOR-inhibitor therapy and aim to integrate this recent data into our current view of the molecular mechanisms of clinically employed mTOR inhibitors and discuss their relevance with special emphasis to transplantation.