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The Janus Kinase/Signal Transducers and Activators of Transcription (JAK/STAT) signaling pathway is utilized by numerous cytokines and interferons, and is essential for the development and function of both innate and adaptive immunity. Aberrant activation of the JAK/STAT pathway is evident in neuroinflammatory diseases such as Multiple Sclerosis and Parkinson’s Disease. Innate immunity is the front line defender of the immune system and is composed of various cell types, including microglia, macrophages and neutrophils. Innate immune responses have both pathogenic and protective roles in neuroinflammation, depending on disease context and the microenvironment in the central nervous system. In this review, we discuss the role of innate immunity in the pathogenesis of neuroinflammatory diseases, how the JAK/STAT signaling pathway regulates the innate immune response, and finally, the potential for ameliorating neuroinflammation by utilization of JAK/STAT inhibitors.

The vacuole is the major site of intracellular Ca 2؉ storage in yeast and functions to maintain cytosolic Ca 2؉ levels within a narrow physiological range. In this study, we examined how cellular Ca 2؉ homeostasis is maintained in a vps33⌬ vacuolar biogenesis mutant. We found that growth of the vps33⌬ strain was sensitive to high or low extracellular Ca 2؉ . This strain could not properly regulate cytosolic Ca 2؉ levels and was able to retain only a small fraction of its total cellular Ca 2؉ in a nonexchangeable intracellular pool. Surprisingly, the vps33⌬ strain contained more total cellular Ca 2؉ than the wild type strain. Because most cellular Ca 2؉ is normally found within the vacuole, this suggested that other intracellular compartments compensated for the reduced capacity to store Ca 2؉ within the vacuole of this strain. To test this hypothesis, we examined the contribution of the Golgi-localized Ca 2؉ ATPase Pmr1p in the maintenance of cellular Ca 2؉ homeostasis. We found that a vps33⌬/pmr1⌬ strain was hypersensitive to high extracellular Ca 2؉ . In addition, certain combinations of mutations effecting both vacuolar and Golgi Ca 2؉ transport resulted in synthetic lethality. These results indicate that the Golgi apparatus plays a significant role in maintaining Ca 2؉ homeostasis when vacuolar biogenesis is compromised.

The JAK/STAT pathway is critical for development, regulation, and termination of immune responses, and dysregulation of the JAK/STAT pathway, that is, hyperactivation, has pathological implications in autoimmune and neuroinflammatory diseases. Suppressor of cytokine signaling 3 (SOCS3) regulates STAT3 activation in response to cytokines that play important roles in the pathogenesis of neuroinflammatory diseases, including IL-6 and IL-23. We previously demonstrated that myeloid lineage-specific deletion of SOCS3 resulted in a severe, nonresolving atypical form of experimental autoimmune encephalomyelitis (EAE), characterized by lesions, inflammatory infiltrates, elevated STAT activation, and elevated cytokine and chemokine expression in the cerebellum. Clinically, these mice exhibit ataxia and tremors. In this study, we provide a detailed analysis of this model, demonstrating that the atypical EAE observed in LysMCre-SOCS3 fl/fl mice is characterized by extensive neutrophil infiltration into the cerebellum and brainstem, increased inducible NO synthase levels in the cerebellum and brainstem, and prominent axonal damage. Importantly, infiltrating SOCS3-deficient neutrophils produce high levels of CXCL2, CCL2, CXCL10, NO, TNF-a, and IL-1b. Kinetic studies demonstrate that neutrophil infiltration into the cerebellum and brainstem of LysMCre-SOCS3 fl/fl mice closely correlates with atypical EAE clinical symptoms. Ab-mediated depletion of neutrophils converts the atypical phenotype to the classical EAE phenotype and, in some cases, a mixed atypical/classical phenotype. Blocking CXCR2 signaling ameliorates atypical EAE development by reducing neutrophil infiltration into the cerebellum/brainstem. Thus, neutrophils lacking SOCS3 display elevated STAT3 activation and expression of proinflammatory mediators and play a critical role in the development of atypical EAE.

Protein kinase CK2 is a serine/threonine kinase composed of two catalytic subunits (CK2α and/or CK2α′) and two regulatory subunits (CK2β). CK2 promotes cancer progression by activating the NF-κB, PI3K/AKT/mTOR, and JAK/STAT pathways, and also is critical for immune cell development and function. The potential involvement of CK2 in CD8+ T cell function has not been explored. We demonstrate that CK2 protein levels and kinase activity are enhanced upon mouse CD8+ T cell activation. CK2α deficiency results in impaired CD8+ T cell activation and proliferation upon TCR stimulation. Furthermore, CK2α is involved in CD8+ T cell metabolic reprogramming through regulating the AKT/mTOR pathway. Lastly, using a mouse Listeria monocytogenes infection model, we demonstrate that CK2α is required for CD8+ T cell expansion, maintenance, and effector function in both primary and memory immune responses. Collectively, our study implicates CK2α as an important regulator of mouse CD8+ T cell activation, metabolic reprogramming, and differentiation both in vitro and in vivo.

IntroductionMyeloid cells play a critical role in the pathogenesis of Inflammatory Bowel Diseases (IBDs), including Ulcerative Colitis (UC) and Crohn’s Disease (CD). Dysregulation of the JAK/STAT pathway is associated with many pathological conditions, including IBD. Suppressors Of Cytokine Signaling (SOCS) are a family of proteins that negatively regulate the JAK/STAT pathway. Our previous studies identified that mice lacking Socs3 in myeloid cells developed a hyper-activated phenotype of macrophages and neutrophils in a pre-clinical model of Multiple Sclerosis.MethodsTo better understand the function of myeloid cell Socs3 in the pathogenesis of colitis, mice with Socs3 deletion in myeloid cells (Socs3ΔLysM) were utilized in a DSS-induced colitis model.ResultsOur results indicate that Socs3 deficiency in myeloid cells leads to more severe colitis induced by DSS, which correlates with increased infiltration of monocytes and neutrophils in the colon and increased numbers of monocytes and neutrophils in the spleen. Furthermore, our results demonstrate that the expression of genes related to the pathogenesis and diagnosis of colitis such as Il1β, Lcn2, S100a8 and S100a9 were specifically enhanced in Socs3-deficient neutrophils localized to the colon and spleen. Conversely, there were no observable differences in gene expression in Ly6C+ monocytes. Depletion of neutrophils using a neutralizing antibody to Ly6G significantly improved the disease severity of DSS-induced colitis in Socs3-deficient mice.DiscussionThus, our results suggest that deficiency of Socs3 in myeloid cells exacerbates DSS-induced colitis and that Socs3 prevents overt activation of the immune system in IBD. This study may provide novel therapeutic strategies to IBD patients with hyperactivated neutrophils.

Parkinson’s Disease (PD) is an age-related, chronic neurodegenerative disorder. At present, there are no therapies to prevent PD progression. Activated microglia and subsequent neuroinflammation associate with the pathogenesis and progression of PD. Accumulation of α-synuclein (α-syn) in the brain is a core feature of PD and leads to microglial activation, inflammatory cytokines/chemokines production and neurodegeneration. Given the importance of the JAK/STAT pathway in activating microglia and inducing cytokine/chemokine expression, we investigated the therapeutic potential of inhibiting the JAK/STAT pathway using the JAK1/2 inhibitor, AZD1480. We utilized an in vivo rat model of PD induced by viral overexpression of α-syn. We find that AZD1480 treatment inhibits α-syn-induced neuroinflammation by inhibiting microglia activation and CD3+ T-cell infiltration, and neurodegeneration by preventing the degeneration of dopaminergic neurons in vivo. In vitro, AZD1480 inhibits α-syn- and IFN-γ-induced MHC Class II, CD40, iNOS, TNF-α and IL-6 expression in microglia and macrophages by reducing STAT1 and STAT3 activation. These results indicate that inhibiting the JAK/STAT pathway can prevent neuroinflammation and neurodegeneration by suppressing activation of innate and adaptive immune responses to α-syn and inflammatory cytokines in this PD model. Furthermore, this suggests the feasibility of targeting the JAK/STAT pathway as neuroprotective therapy for neurodegenerative diseases.

Multiple sclerosis (MS) is associated with a dysregulated JAK/STAT signaling pathway. Suppressors of cytokine signaling (SOCS) negatively regulate the JAK/STAT pathway. MS patients with disease affecting the cerebellum display rapid progression and poor prognosis. Previous data from our laboratory demonstrates a severe, brain-targeted form of experimental autoimmune encephalomyelitis (EAE) in mice lacking Socs3 in myeloid cells (Socs3ΔLysM), with increased cerebellar infiltration of primed neutrophils. Here, we induced EAE in mice lacking Socs3 specifically in neutrophils (Socs3ΔLy6G; n=26) and Ly6G−/+ control mice (n=13), and examined disease progression, neutrophil populations and CD4+ T-cell polarization at disease peak. Ly6G−/+ mice exhibited clinical signs of classical EAE, whereas Socs3ΔLy6G mice exhibited clinical signs of brain-targeted EAE, similar to Socs3ΔLysM mice. An analysis of the cerebellar cell infiltrate in Socs3ΔLy6G mice demonstrated an increased cellularity (p=0.005), which was comprised of both an increase in the percentage (p=0.020) and total number (p<0.001) of cerebellar neutrophils. Neutrophils from Socs3ΔLy6G mice exhibited a primed phenotype with increased surface expression of CD11b (p=0.084) and reduced expression of CD62L (p<0.001). Additionally, Socs3ΔLy6G mice exhibited an increase in the percent of cerebellar CD4+ T-cells (p=0.018) and a shift toward IFN-γ-producing Th1 CD4+ T-cells (p=0.012). These data conclusively document that neutrophil-specific deficiency of Socs3 is sufficient to induce brain-targeted EAE. Future studies will identify targets to dampen the role of neutrophils in brain-targeted autoimmune neuroinflammation.