JAK inhibition and progressive kidney disease

Renal protective effect of Paeoniflorin by inhibition of JAK2/STAT3 signaling pathway in diabetic mice

Paeoniflorin is the main bioactive components of the root of P.lactiflora Pall., and has been widely used as an anti-inflammation and immunomodulatory agent. However, the effect and mechanisms of Paeoniflorin in diabetic nephropathy (DN) remains to be elucidated. In the present study, streptozotocin (STZ)-induced type 1 diabetic mice model was used to investigate the protective effect of Paeoniflorin and the role of the Janus kinase (JAK) 2/signal transducer (STAT) 3 signaling pathway on DN. After treatment with Paeoniflorin at a dose of 25, 50 and 100 mg/kg once a day for 12 weeks, both the functional and histological damage to diabetic mice kidney had been attenuated significantly. Additionally, these reno-protective effects were associated with alleviating macrophage infiltration and inflammatory factors expression as well as suppression of the JAK2/STAT3 signaling pathway. These data reveal that Paeoniflorin attenuates renal lesions in diabetic mice and these protective effects may be associated with the prevention of macrophage infiltration and inhibition of the JAK2/STAT3 signaling pathway.

Protein S Protects against Podocyte Injury in Diabetic Nephropathy

Background Diabetic nephropathy (DN) is a leading cause of ESRD in the United States, but the molecular mechanisms mediating the early stages of DN are unclear.Methods To assess global changes that occur in early diabetic kidneys and to identify proteins potentially involved in pathogenic pathways in DN progression, we performed proteomic analysis of diabetic and nondiabetic rat glomeruli. Protein S (PS) among the highly upregulated proteins in the diabetic glomeruli. PS exerts multiple biologic effects through the Tyro3, Axl, and Mer (TAM) receptors. Because increased activation of Axl by the PS homolog Gas6 has been implicated in DN progression, we further examined the role of PS in DN.Results In human kidneys, glomerular PS expression was elevated in early DN but suppressed in advanced DN. However, plasma PS concentrations did not differ between patients with DN and healthy controls. A prominent increase of PS expression also colocalized with the expression of podocyte markers in early diabetic kidneys. In cultured podocytes, high-glucose treatment elevated PS expression, and PS knockdown further enhanced the high-glucose-induced apoptosis. Conversely, PS overexpression in cultured podocytes dampened the high-glucose- and TNF-α-induced expression of proinflammatory mediators. Tyro3 receptor was upregulated in response to high glucose and mediated the anti-inflammatory response of PS. Podocyte-specific PS loss resulted in accelerated DN in streptozotocin-induced diabetic mice, whereas the transient induction of PS expression in glomerular cells in vivo attenuated albuminuria and podocyte loss in diabetic OVE26 mice.Conclusions Our results support a protective role of PS against glomerular injury in DN progression.

Inflammatory Mechanisms as New Biomarkers and Therapeutic Targets for Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of CKD and end-stage kidney disease (ESKD) worldwide. Approximately 30-40% of people with diabetes develop this microvascular complication, placing them at high risk of losing kidney function as well as of cardiovascular events, infections, and death. Current therapies are ineffective for arresting kidney disease progression and mitigating risks of comorbidities and death among patients with DKD. As the global count of people with diabetes will soon exceed 400 million, the need for effective and safe treatment options for complications such as DKD becomes ever more urgent. Recently, the understanding of DKD pathogenesis has evolved to recognize inflammation as a major underlying mechanism of kidney damage. In turn, inflammatory mediators have emerged as potential biomarkers and therapeutic targets for DKD. Phase 2 clinical trials testing inhibitors of monocyte-chemotactic protein-1 chemokine C-C motif-ligand 2 and the Janus kinase/signal transducer and activator of transcription pathway, in particular, have produced promising results.

AG490, a JAK2-specific inhibitor, downregulates the expression and activity of organic anion transporter-3

Human organic anion transporter-3 (hOAT3) is richly expressed in the kidney, where it plays critical roles in the secretion of clinically important drugs, including anti-viral therapeutics, anti-cancer drugs, antibiotics, antihypertensives, and anti-inflammatories. In the current study, we examined the role of AG490, a specific inhibitor of the Janus tyrosine kinase 2 (JAK2), in hOAT3 transport activity in the kidney COS-7 cells. AG490 induced a time- and concentration-dependent inhibition of hOAT3-mediated uptake of estrone sulfate, a prototypical substrate for the transporter. The inhibitory effect of AG490 correlated with a reduced expression of hOAT3 at the cell surface. Our lab previously demonstrated that Nedd4-2, a ubiquitin ligase, down regulates OAT expression and transport activity by enhancing OAT ubiquitination, which leads to an internalization of OAT from cell surface to intracellular compartments and subsequent degradation. In the current study, we showed that treatment of hOAT3-expressing cells with AG490 resulted in an enhanced hOAT3 ubiquitination and degradation, which was accompanied by a strengthened association of Nedd4-2 with hOAT3 and a reduction in Nedd4-2 phosphorylation. SiRNA knockdown of endogenous Nedd4-2 abrogated the effects of AG490 on hOAT3. In summary, our study demonstrated that AG490 regulates hOAT3 expression and transport activity through the modulation of Nedd4-2.

Protective effects of IFN-γ on the kidney of type- 2 diabetic KKAy mice

BACKGROUND

Development of novel therapeutic strategies that specifically target diabetic kidney disease (DKD) is urgently needed.

METHODS

Male KKAy mice were divided randomly into three equal groups - KK, KI, and KF; Male C57BL/6 mice were the control group. All KKAy mice were fed a high-fat diet. From the 16th week, the KI group was given IFN-γ, and the KF group was assigned to be treated with fludarabine. C57BL/6 mice were always fed a normal mouse diet. Every 4 weeks, body weight, random blood sugar, urine albumin and urea of all mice were measured. At the 20th week, all mice were killed, renal tissue was obtained to observe the pathological manifestations and extract proteins, and transforming growth factor- beta1 (TGF-β1), collagen IV and Janus kinase 2/signal transducers and activators of transcription 1 (JAK2/STAT1) pathway proteins were measured by western blot.

RESULTS

The present study showed that all KKAy mice appeared obese and hyperglycaemic from 12 weeks old and exhibited an increased urine albumin-to-creatinine ratio (ACR) from 16 weeks old. At the 20th week, compared to the KK group, the KI group showed lower ACR, more overexpression of P-STAT1 and less expression of TGF-β1 and collagen IV proteins in renal tissue. The KI group mice showed less accumulation of glomerular mesangial matrix than those in the KK group.

CONCLUSIONS

Our results indicate that IFN-γ might activate STAT1 to suppress the overexpression of TGF-β1 and collagen IV proteins and attenuate the excessive accumulation of mesangial matrix under DKD conditions in KKAy mice.

Therapeutic effects of histone deacetylase inhibitors on kidney disease

Increasing evidence has shown the involvement of histone deacetylases (HDACs) in the development and progression of various renal diseases, highlighting its inhibition as a promising therapeutic strategy to prevent kidney diseases. Accordingly, numerous studies have shown that HDAC inhibitors protect the kidneys from various diseases through their effects on multiple pathways, such as suppression of transforming growth factor-β signaling pathway and nuclear factor-κB signaling pathways, augmentation of apoptosis, and inhibition of angiogenesis. To develop more effective and less toxic isoform-selective HDAC inhibitors and further improve clinical outcomes, it is necessary to identify and understand the mechanisms involved in the pathogenesis and progression of renal diseases. This review focuses on the roles of HDAC inhibitors and the mechanisms involved in their therapeutic effects in experimental models of kidney diseases including glomerulosclerosis, tubulointerstitial fibrosis, glomerular and tubulointerstitial inflammation, lupus nephritis, polycystic kidney disease, and renal cell carcinoma (RCC).

Extracellular Signal-Regulated Kinase 1/2 Regulates Mouse Kidney Injury Molecule-1 Expression Physiologically and Following Ischemic and Septic Renal Injury

The upregulation of kidney injury molecule-1 (KIM-1) has been extensively studied in various renal diseases and following acute injury; however, the initial mechanisms controlling KIM-1 expression remain limited. In this study, KIM-1 expression was examined in mouse renal cell cultures and in two different models of acute kidney injury (AKI), ischemia reperfusion (IR)-induced and lipopolysaccharide (LPS)-induced sepsis. KIM-1 mRNA increased in both AKI models, and pharmacological inhibition of extracellular signal-regulated kinase 1/2 (ERK1/2) signaling attenuated injury-induced KIM-1 expression in the renal cortex. Toll-like receptor 4 knockout (TLR4KO) mice exhibited reduced ERK1/2 phosphorylation and attenuated KIM-1 mRNA after LPS exposure. TLR4KO mice were not protected from IR-induced ERK1/2 phosphorylation and upregulation of KIM-1 mRNA. Following renal IR injury, phosphorylation of signal transducer and activator of transcription 3 (STAT3) at serine 727 and tyrosine 705 increased downstream from ERK1/2 activation. Because phosphorylated STAT3 is a transcriptional upregulator of KIM-1 and inhibition of ERK1/2 attenuated increases in STAT3 phosphorylation, we suggest an ERK1/2-STAT3-KIM-1 pathway following renal injury. Finally, ERK1/2 inhibition in naive mice decreased KIM-1 mRNA and nuclear STAT3 phosphorylation in the cortex, indicating homeostatic regulation of KIM-1. These findings reveal renal ERK1/2 as an important initial regulator of KIM-1 expression in IR and septic AKI and at a physiologic level.Visual Abstract.Proposed mechanism of IR, LPS, and ROS-induced renal damage that initiates ERK1/2 and STAT3 phosphorylation. STAT3 then binds to the KIM-1 promoter and increases KIM-1 mRNA. By preventing ERK1/2 phosphorylation following renal injury, STAT3 phosphorylation is decreased, leading to less phosphorylated STAT3 within the nucleus, and subsequently less KIM-1 mRNA increases post injury.

Defective Suppressor of Cytokine Signaling 1 Signaling Contributes to the Pathogenesis of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a complex autoimmune disease involving injuries in multiple organs and systems. Exaggerated inflammatory responses are characterized as end-organ damage in patients with SLE. Although the explicit pathogenesis of SLE remains unclear, increasing evidence suggests that dysregulation of cytokine signals contributes to the progression of SLE through the Janus kinase/signal transducer and activator of transcription (STAT) signaling pathway. Activated STAT proteins translocate to the cell nucleus and induce transcription of target genes, which regulate downstream cytokine production and inflammatory cell infiltration. The suppressor of cytokine signaling 1 (SOCS1) is considered as a classical inhibitor of cytokine signaling. Recent studies have demonstrated that SOCS1 expression is decreased in patients with SLE and in murine lupus models, and this negatively correlates with the magnitude of inflammation. Dysregulation of SOCS1 signals participates in various pathological processes of SLE such as hematologic abnormalities and autoantibody generation. Lupus nephritis is one of the most serious complications of SLE, and it correlates with suppressed SOCS1 signals in renal tissues. Moreover, SOCS1 insufficiency affects the function of several other organs, including skin, central nervous system, liver, and lungs. Therefore, SOCS1 aberrancy contributes to the development of both systemic and local inflammation in SLE patients. In this review, we discuss recent studies regarding the roles of SOCS1 in the pathogenesis of SLE and its therapeutic implications.

What can target kidney fibrosis?

Fibrosis, a characteristic of all chronic kidney diseases, is now recognized to be an independent predictor of disease progression. Deposition of pathological matrix in the walls of glomerular capillaries, the interstitial space and around arterioles both predicts and contributes to functional demise of the nephron and its surrounding vasculature. Recent identification of the major cell populations of fibroblast precursors in the kidney interstitium as pericytes and tissue-resident mesenchymal stem cells, and in the glomerulus as podocytes, parietal epithelial and mesangial cells, has enabled the study of the fibrogenic process in much greater depth directly in the fibroblast precursors. These cells are not only matrix-producing cells, but are also important innate immune surveillance cells that regulate the inflammatory process, exacerbate tissue damage by release of radicals and cytokines, and contribute to parenchymal and microvascular dysfunction by aberrant wound-healing responses. Innate immune signaling in fibroblasts and their precursors is intimately intertwined with the process of fibrogenesis. In addition, genomic and genetic studies also point to defective responses in loci close to genes involved in solute transport, metabolism, autophagy, protein handling and vascular homeostasis, principally in the epithelium and endothelium, as upstream drivers of the fibrotic process, indicating that cellular crosstalk is vital for development of fibrosis. As we move beyond TGFβ inhibition as a central target for fibrosis, targeting innate immune signaling and metabolic dysfunction appear increasingly tenable alternative targets for novel therapies.

Advanced glycation end products induce the apoptosis of and inflammation in mouse podocytes through CXCL9-mediated JAK2/STAT3 pathway activation

Diabetic nephropathy (DN) is a serious and one of the most common microvascular complications of diabetes. There is accumulating evidence to indicate that advanced glycation end products (AGEs), senescent macroprotein derivatives formed at an accelerated rate under conditions of diabetes, play a role in DN. In this study, we found that the serum and urine levels of C-X-C motif chemokine ligand 9 (CXCL9) were significantly elevated in patients with DN compared with healthy controls. Based on an in vitro model of mouse podocyte injury, AGEs decreased the proliferation of podocytes and increased the expression of CXCL9 and C-X-C motif chemokine receptor 3 (CXCR3), and promoted the activation of signal transducer and activator of transcription 3 (STAT3). The knockdown of CXCL9 by the transfection of mouse podoyctes with specific siRNA significantly increased the proliferation and decreased the apoptosis of the podoyctes. Moreover, the levels of inflammatory factors, such as tumor necrosis factor (TNF)-α and interleukin (IL)-6 were also decreased in the podoyctes transfected with siRNA-CXCL9, accompanied by the increased expression of nephrin and podocin, and decreased levels of Bax/Bcl-2 and activated caspase-3. The knockdown of CXCL9 also led to the inactivation of the Janus kinase 2 (JAK2)/STAT3 pathway. Importantly, the use of the JAK2 inhibitor, AG490, and valsartan (angiotensin II receptor antagonist) attenuated the injury induced to mouse podoyctes by AGEs. On the whole, and to the best of our knowledge, this study demonstrates for the first time that AGEs exert pro-apoptotic and pro-inflammatory effects in mouse podoyctes through the CXCL9-mediated activation of the JAK2/STAT3 pathway. Thus, our data provide a potential therapeutic target for DN.

Diabetic nephropathy - is this an immune disorder?

Chronic diabetes is associated with metabolic and haemodynamic stresses which can facilitate modifications to DNA, proteins and lipids, induce cellular dysfunction and damage, and stimulate inflammatory and fibrotic responses which lead to various types of renal injury. Approximately 30-40% of patients with diabetes develop nephropathy and this renal injury normally progresses in about a third of patients. Due to the growing incidence of diabetes, diabetic nephropathy is now the main cause of end-stage renal disease (ESRD) worldwide. Accumulating evidence from experimental and clinical studies has demonstrated that renal inflammation plays a critical role in determining whether renal injury progresses during diabetes. However, the immune response associated with diabetic nephropathy is considerably different to that seen in autoimmune kidney diseases or in acute kidney injury arising from episodes of ischaemia or infection. This review evaluates the role of the immune system in the development of diabetic nephropathy, including the specific contributions of leucocyte subsets (macrophages, neutrophils, mast cells, T and B lymphocytes), danger-associated molecular patterns (DAMPs), inflammasomes, immunoglobulin and complement. It also examines factors which may influence the development of the immune response, including genetic factors and exposure to other kidney insults. In addition, this review discusses therapies which are currently under development for targeting the immune system in diabetic nephropathy and indicates those which have proceeded into clinical trials.

An Unbiased High-Throughput Screen to Identify Novel Effectors That Impact on Cardiomyocyte Aggregate Levels

RATIONALE

Postmitotic cells, such as cardiomyocytes, seem to be particularly susceptible to proteotoxic stimuli, and large, proteinaceous deposits are characteristic of the desmin-related cardiomyopathies and crystallin cardiomyopathic diseases. Increased activity of protein clearance pathways in the cardiomyocyte, such as proteasomal degradation and autophagy, has proven to be beneficial in maintaining cellular and cardiac function in the face of multiple proteotoxic insults, holding open the possibility of targeting these processes for the development of effective therapeutics.

OBJECTIVE

Here, we undertake an unbiased, total genome screen for RNA transcripts and their protein products that affect aggregate accumulations in the cardiomyocytes.

METHODS AND RESULTS

Primary mouse cardiomyocytes that accumulate aggregates as a result of a mutant CryAB (αB-crystallin) causative for human desmin-related cardiomyopathy were used for a total genome-wide screen to identify gene products that affected aggregate formation. We infected cardiomyocytes using a short hairpin RNA lentivirus library in which the mouse genome was represented. The screen identified multiple candidates in many cell signaling pathways that were able to mediate significant decreases in aggregate levels.

CONCLUSIONS

Subsequent validation of one of these candidates, Jak1 (Janus kinase 1), a tyrosine kinase of the nonreceptor type, confirmed the usefulness of this approach in identifying previously unsuspected players in proteotoxic processes.

Role of the JAK2/STAT3 signaling pathway in the pathogenesis of type 2 diabetes mellitus with macrovascular complications

This study investigated the role of the JAK2/STAT3/SOCS pathway in type 2 diabetes mellitus (T2DM) and macrovascular complications (DV) (T2DM+DV) conditions. Human umbilical vein endothelial cells (HUVECs) were co-cultured with human monocytes (THP-1) and exposed to peripheral blood sera from 30 T2DM patients, 30 patients with T2DM+DV and 30 healthy controls; the groups were divided into the control, T2DM, DV, T2DM+AG490 and DV+AG490 groups. Chemotaxis of treated HUVECs toward THP-1 cells was assessed using Transwell migration. The mRNA expression of JAK2, STAT3, VEGF and FLT1 was evaluated using RT-PCR, whereas the protein levels of ICAM-1, p-JAK2, JAK2, STAT3, p-STAT3, SOCS1 and SOCS3 were determined using western blotting. p-STAT3 was observed using immunofluorescence. The IL-1β concentrations were assessed by ELISA. AG90 was used as a specific inhibitor of JAK2/STAT3 signaling. The chemotaxis assays revealed a migratory order of DV>DM>control, and AG490 treatment decreased chemotaxis. Additionally, p-STAT3 fluorescence was noticeably increased in the DM group and more so in the DV group. The mRNA expression of JAK2, STAT3, VEGF and FLT1 and the protein levels of ICAM-1, p-JAK2, p-STAT3, SOCS1 and SOCS3 were significantly higher in the T2DM and DV groups than in the control group and in the AG490-treated groups than in the untreated groups. The supernatant concentrations of IL-1β in the DV and T2DM groups were higher than those in the control group, and treatment with AG490 decreased the IL-1β concentration. The JAK2/STAT3/SOCS axis contributes to the development of DV by mediating inflammation associated with vascular endothelial cells and/or monocytes.

Specialized pro-resolving mediators in renal fibrosis

Inflammation and its timely resolution play a critical role in effective host defence and wound healing. Unresolved inflammatory responses underlie the pathology of many prevalent diseases resulting in tissue fibrosis and eventual organ failure as typified by kidney, lung and liver fibrosis. The role of autocrine and paracrine mediators including cytokines, prostaglandins and leukotrienes in initiating and sustaining inflammation is well established. More recently a physiological role for specialized pro-resolving lipid mediators [SPMs] in modulating inflammatory responses and promoting the resolution of inflammation has been appreciated. As will be discussed in this review, SPMs not only attenuate the development of fibrosis through promoting the resolution of inflammation but may also directly suppress fibrotic responses. These findings suggest novel therapeutic paradigms to treat intractable life-limiting diseases such as renal fibrosis.

Janus Kinase 2 Regulates Transcription Factor EB Expression and Autophagy Completion in Glomerular Podocytes

The nonreceptor kinase Janus kinase 2 (JAK2) has garnered attention as a promising therapeutic target for the treatment of CKD. However, being ubiquitously expressed in the adult, JAK2 is also likely to be necessary for normal organ function. Here, we investigated the phenotypic effects of JAK2 deficiency. Mice in which JAK2 had been deleted from podocytes exhibited an elevation in urine albumin excretion that was accompanied by increased podocyte autophagosome fractional volume and p62 aggregation, which are indicative of impaired autophagy completion. In cultured podocytes, knockdown of JAK2 similarly impaired autophagy and led to downregulation in the expression of lysosomal genes and decreased activity of the lysosomal enzyme, cathepsin D. Because transcription factor EB (TFEB) has recently emerged as a master regulator of autophagosome-lysosome function, controlling the expression of several of the genes downregulated by JAK2 knockdown, we questioned whether TFEB is regulated by JAK2. In immortalized mouse podocytes, JAK2 knockdown decreased TFEB promoter activity, expression, and nuclear localization. In silico analysis and chromatin immunoprecipitation assays revealed that the downstream mediator of JAK2 signaling STAT1 binds to the TFEB promoter. Finally, overexpression of TFEB in JAK2-deficient podocytes reversed lysosomal dysfunction and restored albumin permselectivity. Collectively, these observations highlight the homeostatic actions of JAK2 in podocytes and the importance of TFEB to autophagosome-lysosome function in these cells. These results also raise the possibility that therapeutically modulating TFEB activity may improve podocyte health in glomerular disease.

Suppressor of Cytokine Signaling-1 Peptidomimetic Limits Progression of Diabetic Nephropathy

Diabetes is the main cause of CKD and ESRD worldwide. Chronic activation of Janus kinase and signal transducer and activator of transcription (STAT) signaling contributes to diabetic nephropathy by inducing genes involved in leukocyte infiltration, cell proliferation, and extracellular matrix accumulation. This study examined whether a cell-permeable peptide mimicking the kinase-inhibitory region of suppressor of cytokine signaling-1 (SOCS1) regulatory protein protects against nephropathy by suppressing STAT-mediated cell responses to diabetic conditions. In a mouse model combining hyperglycemia and hypercholesterolemia (streptozotocin diabetic, apoE-deficient mice), renal STAT activation status correlated with the severity of nephropathy. Notably, compared with administration of vehicle or mutant inactive peptide, administration of the SOCS1 peptidomimetic at either early or advanced stages of diabetes ameliorated STAT activity and resulted in reduced serum creatinine level, albuminuria, and renal histologic changes (mesangial expansion, tubular injury, and fibrosis) over time. Mice treated with the SOCS1 peptidomimetic also exhibited reduced kidney leukocyte recruitment (T lymphocytes and classic M1 proinflammatory macrophages) and decreased expression levels of proinflammatory and profibrotic markers that were independent of glycemic and lipid changes. In vitro, internalized peptide suppressed STAT activation and target gene expression induced by inflammatory and hyperglycemic conditions, reduced migration and proliferation in mesangial and tubuloepithelial cells, and altered the expression of cytokine-induced macrophage polarization markers. In conclusion, our study identifies SOCS1 mimicking as a feasible therapeutic strategy to halt the onset and progression of renal inflammation and fibrosis in diabetic kidney disease.

JAK inhibition in the treatment of diabetic kidney disease

Diabetic kidney disease (DKD) is the most common cause of kidney failure in many countries today, but treatments have not improved in the last 20 years. Recently, systems biology methods have allowed the elucidation of signalling pathways and networks involved in the progression of DKD that were not well appreciated previously. A prominent pathway found to be integrally associated with DKD progression is the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway. Increased expression of JAK-STAT genes was found in multiple cells in the kidney, including glomerular podocytes, in both early and progressive DKD. Subsequent experiments in a mouse diabetic model showed that enhanced expression of JAK2 selectively in glomerular podocytes increased functional and pathological features of DKD. Finally, a yet unpublished Phase 2 multicentre, randomised, double-blind, placebo-controlled study of the efficacy of a selective JAK1 and JAK2 inhibitor has been conducted in type 2 diabetic participants with DKD. In this trial there was a reduction of albuminuria in participants who received the active inhibitor compared with those who received a placebo These results support the further study of JAK inhibitors as a new therapy for DKD. This review summarises a presentation given at the 'Anti-inflammatory interventions in diabetes' symposium at the 2015 annual meeting of the EASD. It is accompanied by an overview by the Session Chair, Hiddo Heerspink (DOI: 10.1007/s00125-016-4030-4 ).

Emerging therapeutics for the treatment of diabetic nephropathy

Diabetic nephropathy (DN) is the most common pathology contributing to the development of chronic kidney disease (CKD). DN caused by hypertension and unmitigated inflammation in diabetics, renders the kidneys unable to perform normally, and leads to renal fibrosis and organ failure. The increasing global prevalence of DN has been directly attributed to rising incidences of Type II diabetes, and is now the largest non-communicable cause of death worldwide. Despite the high morbidity, successful new treatments for DN are lacking. This review seeks to provide new insight on emerging clinical candidates under investigation for the treatment of DN.

Drug discovery in focal and segmental glomerulosclerosis

Despite the high medical burden experienced by patients with focal segmental glomerulosclerosis, the etiology of the condition remains largely unknown. Focal segmental glomerulosclerosis is highly heterogeneous in clinical and morphologic manifestations. While this presents challenges for the development of new treatments, research investments over the last 2 decades have yielded a surfeit of potential avenues for therapeutic intervention. The development of many of those ideas and concepts into new therapies, however, has been very disappointing. Here, we describe some of the factors that have potentially contributed to the poor translational performance from this research investment, including the confidence we ascribe to a target, the conduct of experimental studies, and the availability of selective reagents to test hypotheses. We will discuss the significance of genetic and systems traits as well as other methods for reducing bias. We will analyze the limitations of a successful drug development. We will use specific examples hoping that these will guide a consensus for investment and drive greater translational quality. We hope that this substrate will serve to exemplify the tremendous opportunity for intervention as well as facilitate greater collaborative effort between industry, academia, and private foundations in promoting appropriate validation of these targets. Only then will we have achieved our goal for curative therapies for this devastating disease.

Transcriptional networks of murine diabetic peripheral neuropathy and nephropathy: common and distinct gene expression patterns

AIMS/HYPOTHESIS

Diabetic peripheral neuropathy (DPN) and diabetic nephropathy (DN) are two common microvascular complications of type 1 and type 2 diabetes mellitus that are associated with a high degree of morbidity. In this study, using a variety of systems biology approaches, our aim was to identify common and distinct mechanisms underlying the pathogenesis of these two complications.

METHODS

Our previously published transcriptomic datasets of peripheral nerve and kidney tissue, derived from murine models of type 1 diabetes (streptozotocin-injected mice) and type 2 diabetes (BKS-db/db mice) and their respective controls, were collected and processed using a unified analysis pipeline so that comparisons could be made. In addition to looking at genes and pathways dysregulated in individual datasets, pairwise comparisons across diabetes type and tissue type were performed at both gene and transcriptional network levels to complete our proposed objective.

RESULTS

Gene-level analysis identified exceptionally high levels of concordant gene expression in DN (94% of 2,433 genes), but not in DPN (54% of 1,558 genes), between type 1 diabetes and type 2 diabetes. These results suggest that common pathogenic mechanisms exist in DN across diabetes type, while in DPN the mechanisms are more distinct. When these dysregulated genes were examined at the transcriptional network level, we found that the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway was significantly dysregulated in both complications, irrespective of diabetes type.

CONCLUSIONS/INTERPRETATION

Using a systems biology approach, our findings suggest that common pathogenic mechanisms exist in DN across diabetes type, while in DPN the mechanisms are more distinct. We also found that JAK-STAT signalling is commonly dysregulated among all datasets. Using such approaches, further investigation is warranted to determine whether the same changes are observed in patients with diabetic complications.

Inflammation and Fibrosis in ADPKD

Diverse signaling pathways have been reported to be associated with polycystic kidney disease (PKD). Cell proliferation is widely known to be an important pathway related to this disease. However, studies on the interactions of inflammation and fibrosis with polycystic kidney disease have been limited. Inflammation is one of the protective systems involved in the response to foreign molecules. In PKD, it was reported that the activity of signaling pathways associated with inflammation is increased. Also, fibrosis is the development of excess fibrous tissue in organ or tissue. It is an abnormal phenomenon in which the extent of fibrous connective tissues is increased. In PKD, increases in the activity of molecules such as growth factor and TGF-β have been reported to occur and promote fibrosis. Therefore, the inflammation and fibrosis responses have been suggested as therapeutic targets for PKD. In order to guide further studies, this review indicates the roles of inflammatory and fibrosis signaling in PKD.

Retinal Failure in Diabetes: a Feature of Retinal Sensory Neuropathy

Physiologic adaptations mediate normal responses to short-term and long-term stresses to ensure organ function. Organ failure results if adaptive responses fail to resolve persistent stresses or maladaptive reactions develop. The retinal neurovascular unit likewise undergoes adaptive responses to diabetes resulting in a retinal sensory neuropathy analogous to other sensory neuropathies. Vision-threatening diabetic retinal neuropathy results from unremitting metabolic and inflammatory stresses, leading to macular edema and proliferative diabetic retinopathy, states of "retinal failure." Current regulatory strategies focus primarily on the retinal failure stages, but new diagnostic modalities and understanding of the pathophysiology of diabetic retinopathy may facilitate earlier treatment to maintain vision in persons with diabetes.

Present and future in the treatment of diabetic kidney disease

Diabetic kidney disease is the leading cause of end-stage renal disease. Albuminuria is recognized as the most important prognostic factor for chronic kidney disease progression. For this reason, blockade of renin-angiotensin system remains the main recommended strategy, with either angiotensin converting enzyme inhibitors or angiotensin II receptor blockers. However, other antiproteinuric treatments have begun to be studied, such as direct renin inhibitors or aldosterone blockers. Beyond antiproteinuric treatments, other drugs such as pentoxifylline or bardoxolone have yielded conflicting results. Finally, alternative pathogenic pathways are being explored, and emerging therapies including antifibrotic agents, endothelin receptor antagonists, or transcription factors show promising results. The aim of this review is to explain the advances in newer agents to treat diabetic kidney disease, along with the background of the renin-angiotensin system blockade.