Complex systems biology approach to understanding coordination of JAK-STAT signaling

Priming of microglia with IFN-γ impairs adult hippocampal neurogenesis and leads to depression-like behaviors and cognitive defects

Neuroinflammation driven by interferon-gamma (IFN-γ) and microglial activation has been linked to neurological disease. However, the effects of IFN-γ-activated microglia on hippocampal neurogenesis and behavior are unclear. In the present study, IFN-γ was administered to mice via intracerebroventricular injection. Mice received intraperitoneal injection of ruxolitinib to inhibit the JAK/STAT1 pathway or injection of minocycline to inhibit microglial activation. During a 7-day period, mice were assessed for depressive-like behaviors and cognitive impairment based on a series of behavioral analyses. Effects of the activated microglia on neural stem/precursor cells (NSPCs) were examined, as was pro-inflammatory cytokine expression by activated microglia. We showed that IFN-γ-injected animals showed long-term adult hippocampal neurogenesis reduction, behavior despair, anhedonia, and cognitive impairment. Chronic activation with IFN-γ induces reactive phenotypes in microglia associated with morphological changes, population expansion, MHC II and CD68 up-regulation, and pro-inflammatory cytokine (IL-1β, TNF-α, IL-6) and nitric oxide (NO) release. Microglia isolated from the hippocampus of IFN-γ-injected mice suppressed NSPCs proliferation and stimulated apoptosis of immature neurons. Inhibiting of the JAK/STAT1 pathway in IFN-γ-injected animals to block microglial activation suppressed microglia-mediated neuroinflammation and neurogenic injury, and alleviated depressive-like behaviors and cognitive impairment. Collectively, these findings suggested that priming of microglia with IFN-γ impairs adult hippocampal neurogenesis and leads to depression-like behaviors and cognitive defects. Targeting microglia by modulating levels of IFN-γ the brain may be a therapeutic strategy for neurodegenerative diseases and psychiatric disorders.

The Role of Inflammation in the Treatment of Schizophrenia

Background: Inflammation plays a major role in the onset and maintenance of schizophrenia. The objective of the present work was to synthetize in a narrative review the recent findings in the field of inflammation in schizophrenia and their application in daily practice. Method: This review was based on the most recent meta-analyses and randomized controlled trials. Results: The disturbed cytokines depend on the phase of the illness. A meta-analysis of cytokines in schizophrenia found higher levels of pro-inflammatory and anti-inflammatory cytokines in the peripheral blood in both patients with first-episode schizophrenia and relapsed patients than in healthy controls. Exploring detailed data on immune-inflammatory disturbances in SZ reveals that IL-6 is one of the most consistently disturbed cytokines. Other cytokines, including IL1, TNF, and IFN, are also disturbed in schizophrenia. Choosing a broad spectrum anti-inflammatory agent that may inhibit subsequent pathways might be particularly useful for the treatment of inflammatory schizophrenia. Highly sensitive C-Reactive Protein is a useful screening marker for detecting inflammation in SZ subjects. Anti-inflammatory agents have shown effectiveness in recently published meta-analyses. Only one study found a significant difference between celecoxib and placebo, but two found a trend toward significance on illness severity and one on positive symptoms. In addition, other published and unpublished data were included in another meta-analysis that concluded the significant effect of add-on celecoxib in positive symptoms in first episode patients. There is a lack of data to determine if aspirin is truly effective in schizophrenia to date. Other anti-inflammatory agents have been explored, including hormonal therapies, antioxidants, omega 3 fatty acids, and minocycline, showing significant effects for reducing total, positive, and negative score symptoms and general functioning. However, each of these agents has multiple properties beyond inflammation and it remains unclear how these drugs improve schizophrenia. Conclusion: The next step is to tailor anti-inflammatory therapy in schizophrenia, with two main challenges: 1. To provide a more efficient anti-inflammatory therapeutic approach that targets specific pathways associated with the pathology of schizophrenia. 2. To develop a more personalized approach in targeting patients who have the best chance of successful treatment.

Phosphocreatine Improves Cardiac Dysfunction by Normalizing Mitochondrial Respiratory Function through JAK2/STAT3 Signaling Pathway In Vivo and In Vitro

Diabetic cardiomyopathy (DCM) is one of the common cardiovascular complications in patients with diabetes. Accumulating evidence has demonstrated that DCM is thoroughly related to mitochondrial energy impairment and increases the generation of reactive oxygen species (ROS). Therefore, an ongoing study is developing strategies to protect cardiac mitochondria from diabetic complications, especially from hyperglycemia. Phosphocreatine (PCr) plays a major metabolic role in cardiac muscular cells including intracellular concentration of ATP which affects the activity of the myocardium. We hypothesized that PCr might improve oxidative phosphorylation and electron transport capacity in mitochondria impaired by hyperglycemia in vivo and in vitro. Also, we aimed to evaluate the protective effect of PCr against DCM through the JAK2/STAT3 signaling pathway. The mitochondrial respiratory capacity from rats and H9C2 cells was measured by high-resolution respirometry (HRR). Expressions of proteins Bax, Bcl-2, caspase 3, caspase 9, cleaved caspase 3, and cleaved caspase 9, as well as JAK2/STAT3 signaling pathways, were determined by western blotting. ROS generation and mitochondrial membrane potential (MMP) were measured with fluorescent probes. Type 1 diabetes mellitus was induced in Wistar male rats by a single intraperitoneal injection of streptozotocin (STZ) (80 mg/kg body weight). Our results revealed that PCr possessed protective effects against DCM injury by improving the mitochondrial bioenergetics and by positively exerting protective effects against DCM in vivo and in vitro, not only improving diabetes symptom, resulting in changes of cardiac tissue using hematoxylin and eosin (H&E) stain, but also ameliorating biochemical changes. Moreover, PCr increased Bcl-2, caspase 3, and caspase 9 protein expressions and decreased Bax, cleaved caspase 3, and cleaved caspase 9 expressions as well as the JAK2/STAT3 signaling pathway. In conclusion, PCr improves mitochondrial functions and exerts an antiapoptotic effect in vivo and in vitro exposed to oxidative stress by hyperglycemia through the JAK2/STAT3 signaling pathway. Our findings suggest that PCr medication is a possible therapeutic strategy for cardioprotection.

Circulating leptin level in rheumatoid arthritis and its correlation with disease activity: a meta-analysis

OBJECTIVE

This study aimed to evaluate the relationship between the circulating serum leptin level and rheumatoid arthritis (RA) and to establish a correlation between serum leptin levels and RA activity.

METHODS

We searched the PUBMED, EMBASE, and Cochrane databases. A meta-analysis was performed, comparing the serum/plasma leptin levels in patients with RA and healthy controls. Correlation coefficients between serum leptin level and either disease activity score 28 (DAS28) or C‑reactive protein (CRP) in RA patients were also examined.

RESULTS

Thirteen studies with a total of 648 RA patients and 426 controls were included in this meta-analysis. Circulating leptin level was significantly higher in the RA group than in the control group (SMD = 1.056, 95 % CI = 0.647-1.465, p = 4.2 × 10^-7). In addition, stratification by ethnicity showed a significantly elevated leptin level in the RA group in Caucasian, Turkish, and Arab populations (SMD = 0.813, 95 % CI = 0.137-1.490, p = 0.018, SMD = 0.981, 95 % CI = 0.307-1.655, p = 0.004, and SMD = 1.469, 95 % CI = 0.443-2.495, p = 0.005 respectively). A meta-analysis of correlation coefficients showed a small but significantly positive correlation between the circulating leptin level and either DAS28 (correlation coefficient = 0.275, 95 % CI = 0.076-0.452, p = 0.007) or CRP (correlation coefficient = 0.274, 95 % CI = 0.068-0.458, p = 0.010).

CONCLUSIONS

Our meta-analysis demonstrated that the circulating leptin level is significantly higher in patients with RA and that a small but significantly positive correlation exists between leptin levels and RA activity.

Caffeic acid phenethyl ester protects the brain against hexavalent chromium toxicity by enhancing endogenous antioxidants and modulating the JAK/STAT signaling pathway

Hexavalent chromium [Cr(VI)] is commonly used in industry, and is a proven toxin and carcinogen. However, the information regarding its neurotoxic mechanism is not completely understood. The present study was designed to scrutinize the possible protective effects of caffeic acid phenethyl ester (CAPE), a bioactive phenolic of propolis extract, on Cr(VI)-induced brain injury in rats, with an emphasis on the JAK/STAT signaling pathway. Rats received 2mg/kgK₂CrO₄ and concurrently treated with 20mg/kg CAPE for 30 days. Cr(VI)-induced rats showed a significant increase in cerebral lipid peroxidation, nitric oxide and pro-inflammatory cytokines, with concomitantly declined antioxidants and acetylcholinesterase. CAPE attenuated oxidative stress and inflammation and enhanced antioxidant defenses in the cerebrum of rats. Cr(VI) significantly up-regulated JAK2, STAT3 and SOCS3, an effect that was reversed by CAPE. In conclusion, CAPE protects the brain against Cr(VI) toxicity through abrogation of oxidative stress, inflammation and down-regulation of JAK2/STAT3 signaling in a SOCS3-independent mechanism.

Cardiac oxidative stress in diabetes: Mechanisms and therapeutic potential

Macrovascular complications of diabetes, including diabetic cardiovascular disease (CVD), occur through a number of hyperglycaemia-induced mechanisms that include generation of oxidative stress, accumulation of advanced glycation end-products (AGE) and activation of protein kinase C (PKC). Cardiac oxidative stress is associated with increased cardiac fibrosis and hypertrophy, and reduced cardiac performance and contractility, leading to severe cardiac dysfunction and potentially fatal cardiac events. It occurs under conditions of excessive synthesis of reactive oxygen species (ROS). The ensuing activation of transcription factors such as nuclear factor-κB produces inflammation, fibrosis, hypertrophy and further oxidative stress, which itself causes DNA and membrane damage. This review summarises the mechanisms that generate ROS in the diabetic heart: mitochondrial electron leakage, activity of ROS-generating enzymes such as NADPH oxidase, xanthine oxidase and 12/15 lipoxygenase, uncoupling of nitric oxide synthase, accumulation of AGEs and activation of PKC. There is interaction between many of these ROS-generating pathways, with data from a range of published studies indicating that a common upstream pathway is the interaction of AGEs with their receptor (RAGE), which further promotes ROS synthesis. Therefore, agents targeted at decreasing ROS production have been investigated for prevention or treatment of diabetic CVD through reducing oxidative stress, and this review considers some of the studies carried out with anti-oxidant therapies and the feasibility of this approach for protecting against diabetic cardiomyopathy.

Sitagliptin attenuates cardiomyopathy by modulating the JAK/STAT signaling pathway in experimental diabetic rats

Sitagliptin, a dipeptidyl peptidase-4 inhibitor, has been reported to promote cardioprotection in diabetic hearts by limiting hyperglycemia and hyperlipidemia. However, little is known about the involvement of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway modulation in the cardioprotective effects of sitagliptin. The current study aimed to investigate the protective effects of sitagliptin against diabetic cardiomyopathy (DCM), focusing on the modulation of the JAK/STAT pathway. Diabetes was induced by streptozotocin injection, and rats received sitagliptin orally and daily for 90 days. Diabetic rats exhibited hyperglycemia, hyperlipidemia, and a significant increase in heart-to-body weight (HW/BW) ratio. Serum troponin I and creatine kinase MB, cardiac interleukin-6 (IL-6), lipid peroxidation, and nitric oxide levels showed significant increase in diabetic rats. In contrast, both enzymatic and nonenzymatic antioxidant defenses were significantly declined in the heart of diabetic rats. Histopathological study revealed degenerations, increased collagen deposition in the heart of diabetic rats. Sitagliptin alleviated hyperglycemia, hyperlipidemia, HW/BW ratio, histological architecture, oxidative stress, and inflammation, and rejuvenated the antioxidant defenses. In addition, cardiac levels of pJAK2 and pSTAT3 were increased in diabetic rats, an effect which was remarkably decreased after sitagliptin treatment. In conclusion, these results confer an evidence that sitagliptin has great therapeutic potential on DCM through down-regulation of the JAK/STAT signaling pathway.

Possible involvement of the JAK/STAT signaling pathway in N-acetylcysteine-mediated antidepressant-like effects

Advances in depression research have targeted inflammation and oxidative stress to develop novel types of treatment. The JAK/STAT signaling pathway plays pivotal roles in immune and inflammatory responses. The present study was designed to investigate the effects of N-acetylcysteine, a putative precursor of the antioxidant glutathione, in an animal model of depression, with an emphasis on the JAK/STAT signaling pathway. Fluoxetine, a classical antidepressant drug was also under investigation. Male Wistar rats were subjected to forced swimming test and given N-acetylcysteine and fluoxetine immediately after the pre-test session, 5 h later and 1 h before the test session of the forced swimming test. N-acetylcysteine decreased immobility time (P < 0.05), serum corticosterone (P < 0.001), and hydrogen peroxide (P < 0.001), while restored glutathione concentration. Treatment of the rats with N-acetylcysteine produced significant (P < 0.001) down-regulation of STAT3 mRNA expression and protein phosphorylation. On the other hand, N-acetylcysteine significantly (P < 0.001) increased SOCS3 gene expression; however, SOCS3 protein was not changed. In conclusion, our study suggests that modulation of the JAK/STAT pathway might mediate the antidepressant-like effects of N-acetylcysteine. Therefore, depression research may target the JAK/STAT signaling pathway to provide a novel effective therapy.

Emerging role of leptin in rheumatoid arthritis

Numerous studies have suggested the importance of leptin against autoimmune diseases such as systemic lupus erythematosus (SLE), multiple sclerosis (MS) and psoriasis. To summarize our current understanding of the role of leptin in inflammatory responses and rheumatoid arthritis (RA), a systematic review was conducted to assess the discrepancy of leptin in RA and its effect on immunity according to different studies. Recently, emerging data have indicated that leptin is involved in the pathological function of RA, which is common in autoimmune disorders. This review discusses the possible consequences of leptin levels in RA. Blocking the key signal pathways of leptin and inhibiting the leptin activity-like leptin antagonist may be a promising way for potential therapeutic treatment of RA at risk of detrimental effects. However, leptin was increased in patients with RA and may also regulate joint damage. Thus, more understanding of the mechanism of leptin in RA would be advantageous in the future.

Transient oscillatory dynamics of interferon beta signaling in macrophages

Background

Interferon-beta (IFN-beta) activates the immune response through the type I IFN signaling pathway. IFN-beta is important in the response to pathogen infections and is used as a therapy for Multiple Sclerosis. The mechanisms of self-regulation and control of this pathway allow precise and environment-dependent response of the cells in different conditions. Here we analyzed type I IFN signaling in response to IFN-beta in the macrophage cell line RAW 264.7 by RT-PCR, ELISA and xMAP assays. The experimental results were interpreted by means of a theoretical model of the pathway.

Results

Phosphorylation of the STAT1 protein (pSTAT1) and mRNA levels of the pSTAT1 inhibitor SOCS1 displayed an attenuated oscillatory behavior after IFN-beta activation. In turn, mRNA levels of the interferon regulatory factor IRF1 grew rapidly in the first 50–90 minutes after stimulation until a maximum value, and started to decrease slowly around 200–250 min. The analysis of our kinetic model identified a significant role of the negative feedback from SOCS1 in driving the observed damped oscillatory dynamics, and of the positive feedback from IRF1 in increasing STAT1 basal levels. Our study shows that the system works as a biological damped relaxation oscillator based on a phosphorylation-dephosphorylation network centered on STAT1. Moreover, a bifurcation analysis identified translocation of pSTAT1 dimers to the nucleus as a critical step for regulating the dynamics of type I IFN pathway in the first steps, which may be important in defining the response to IFN-beta therapy.

Conclusions

The immunomodulatory effect of IFN-beta signaling in macrophages takes the form of transient oscillatory dynamics of the JAK-STAT pathway, whose specific relaxation properties determine the lifetime of the cellular response to the cytokine.

Systematic analysis of the mechanisms of virus-triggered type I IFN signaling pathways through mathematical modeling

Based on biological experimental data, we developed a mathematical model of the virus-triggered signaling pathways that lead to induction of type I IFNs and systematically analyzed the mechanisms of the cellular antiviral innate immune responses, including the negative feedback regulation of ISG56 and the positive feedback regulation of IFNs. We found that the time between 5 and 48 hours after viral infection is vital for the control and/or elimination of the virus from the host cells and demonstrated that the ISG56-induced inhibition of MITA activation is stronger than the ISG56-induced inhibition of TBK1 activation. The global parameter sensitivity analysis suggests that the positive feedback regulation of IFNs is very important in the innate antiviral system. Furthermore, the robustness of the innate immune signaling network was demonstrated using a new robustness index. These results can help us understand the mechanisms of the virus-induced innate immune response at a system level and provide instruction for further biological experiments.

Computational models of the JAK1/2-STAT1 signaling

Despite a conceptually simple mechanism of signaling, the JAK-STAT pathway exhibits considerable behavioral complexity. Computational pathway models are tools to investigate in detail signaling process. They integrate well with experimental studies, helping to explain molecular dynamics and to state new hypotheses, most often about the structure of interactions. A relatively small amount of experimental data is available for a JAK1/2-STAT1 variant of the pathway, hence, only several computational models were developed. Here we review a dominant approach of kinetic modeling of the JAK1/2-STAT1 pathway, based on ordinary differential equations. We also give a brief overview of attempts to computationally infer topology of this pathway.

Modeling and dynamical analysis of virus-triggered innate immune signaling pathways

The investigation of the dynamics and regulation of virus-triggered innate immune signaling pathways at a system level will enable comprehensive analysis of the complex interactions that maintain the delicate balance between resistance to infection and viral disease. In this study, we developed a delayed mathematical model to describe the virus-induced interferon (IFN) signaling process by considering several key players in the innate immune response. Using dynamic analysis and numerical simulation, we evaluated the following predictions regarding the antiviral responses: (1) When the replication ratio of virus is less than 1, the infectious virus will be eliminated by the immune system’s defenses regardless of how the time delays are changed. (2) The IFN positive feedback regulation enhances the stability of the innate immune response and causes the immune system to present the bistability phenomenon. (3) The appropriate duration of viral replication and IFN feedback processes stabilizes the innate immune response. The predictions from the model were confirmed by monitoring the virus titer and IFN expression in infected cells. The results suggest that the balance between viral replication and IFN-induced feedback regulation coordinates the dynamical behavior of virus-triggered signaling and antiviral responses. This work will help clarify the mechanisms of the virus-induced innate immune response at a system level and provide instruction for further biological experiments.

Division of labor by dual feedback regulators controls JAK2/STAT5 signaling over broad ligand range

Cellular signal transduction is governed by multiple feedback mechanisms to elicit robust cellular decisions. The specific contributions of individual feedback regulators, however, remain unclear. Based on extensive time-resolved data sets in primary erythroid progenitor cells, we established a dynamic pathway model to dissect the roles of the two transcriptional negative feedback regulators of the suppressor of cytokine signaling (SOCS) family, CIS and SOCS3, in JAK2/STAT5 signaling. Facilitated by the model, we calculated the STAT5 response for experimentally unobservable Epo concentrations and provide a quantitative link between cell survival and the integrated response of STAT5 in the nucleus. Model predictions show that the two feedbacks CIS and SOCS3 are most effective at different ligand concentration ranges due to their distinct inhibitory mechanisms. This divided function of dual feedback regulation enables control of STAT5 responses for Epo concentrations that can vary 1000-fold in vivo. Our modeling approach reveals dose-dependent feedback control as key property to regulate STAT5-mediated survival decisions over a broad range of ligand concentrations.

Systems biology of JAK-STAT signalling in human malignancies

Originally implicated in the regulation of survival, proliferation and differentiation of haematopoietic cells, the JAK-STAT pathway has also been linked to developmental processes, growth control and maintenance of homeostasis in a variety of other cells and tissues. Although it remains a complex system, its relative simplicity and the availability of molecular data makes it particularly attractive for modelling approaches. In this review, we will focus on JAK-STAT signalling in the context of cancer and present efforts to investigate signalling dynamics with the help of mathematical models. We describe the modelling workflow that realises a systems biology approach and give an example for interferon-γ signalling in pancreatic stellate cells.

Understanding inhibition of viral proteins on type I IFN signaling pathways with modeling and optimization

The interferon system provides a powerful and universal intracellular defense mechanism against viruses. As one part of their survival strategies, many viruses have evolved mechanisms to counteract the host type I interferon (IFN-alpha/beta) responses. In this study, we attempt to investigate virus- and double-strand RNA (dsRNA)-triggered type I IFN signaling pathways and understand the inhibition of IFN-alpha/beta induction by viral proteins using mathematical modeling and quantitative analysis. Based on available literature and our experimental data, we develop a mathematical model of virus- and dsRNA-triggered signaling pathways leading to type I IFN gene expression during the primary response, and use the genetic algorithm to optimize all rate constants in the model. The consistency between numerical simulation results and biological experimental data demonstrates that our model is reasonable. Further, we use the model to predict the following phenomena: (1) the dose-dependent inhibition by classical swine fever virus (CSFV) N(pro) or E(rns) protein is observed at a low dose and can reach a saturation above a certain dose, not an increase; (2) E(rns) and N(pro) have no synergic inhibitory effects on IFN-beta induction; (3) the different characters in an important transcription factor, phosphorylated IRF3 (IRF3p), are exhibited because N(pro) or E(rns) counteracted dsRNA- and virus-triggered IFN-beta induction by targeting the different molecules in the signaling pathways and (4) N(pro) inhibits the IFN-beta expression not only by interacting with IFR3 but also by affecting its complex with MITA. Our approaches help to gain insight into system properties and rational therapy design, as well as to generate hypotheses for further research.

Comparative analysis of the JAK/STAT signaling through erythropoietin receptor and thrombopoietin receptor using a systems approach

Background

The Janus kinase-signal transducer and activator of transcription (JAK/STAT) pathway is one of the most important targets for myeloproliferative disorder (MPD). Although several efforts toward modeling the pathway using systems biology have been successful, the pathway was not fully investigated in regard to understanding pathological context and to model receptor kinetics and mutation effects.

Results

We have performed modeling and simulation studies of the JAK/STAT pathway, including the kinetics of two associated receptors (the erythropoietin receptor and thrombopoietin receptor) with the wild type and a recently reported mutation (JAK2V617F) of the JAK2 protein.

Conclusion

We found that the different kinetics of those two receptors might be important factors that affect the sensitivity of JAK/STAT signaling to the mutation effect. In addition, our simulation results support clinically observed pathological differences between the two subtypes of MPD with respect to the JAK2V617F mutation.

Systems biology of JAK/STAT signalling

Signalling in multicellular organisms is mediated by complex networks that integrate extracellular and intracellular signals to generate appropriate responses regulating cell proliferation, differentiation and survival. Downstream of many cytokine and growth hormone receptors, receptor-associated JAKs (Janus kinases) activate transcription factors of the STAT (signal transducer and activator of transcription) protein family and thereby mediate signal transduction from the plasma membrane to the nucleus. The JAK/STAT pathway has been shown to be constitutively activated in a wide array of human malignancies. To elucidate mechanisms contributing to tumour formation and identify system properties of the JAK/STAT signalling pathway, a systems biology approach can be employed. So far the majority of studies available have focused on down-regulation of the signalling pathway based on simulations. However, a data-based model of the core module of the JAK2/STAT5 signalling pathway showed that rapid nucleocytoplasmic cycling of STAT5 is an essential pathway property. In the future, combining assays for quantitative analysis at different levels will be important to gain deeper insight into molecular mechanisms regulating intracellular communication mediated by such complex dynamic systems as signalling pathways and their targets.