Loss of Mef2D function enhances TLR induced IL-10 production in macrophages.

Mef2 transcription factors comprise a family of four different isoforms that regulate a number of processes including neuronal and muscle development. While roles for Mef2C and Mef2D have been described in B-cell development their role in immunity has not been extensively studied. In innate immune cells such as macrophages, TLRs drive the production of both pro- and anti-inflammatory cytokines. IL-10 is an important anti-inflammatory cytokine produced by macrophages and it establishes an autocrine feedback loop to inhibit pro-inflammatory cytokine production. We show here that macrophages from Mef2D knockout mice have elevated levels of IL-10 mRNA induction compared with wild-type cells following LPS stimulation. The secretion of IL-10 was also higher from Mef2D knockout macrophages and this correlated to a reduction in the secretion of TNF, IL-6 and IL-12p40. The use of an IL-10 neutralising antibody showed that this reduction in pro-inflammatory cytokine production in the Mef2D knockouts was IL-10 dependent. As the IL-10 promoter has previously been reported to contain a potential binding site for Mef2D, it is possible that the binding of other Mef2 isoforms in the absence of Mef2D may result in a higher activation of the IL-10 gene. Further studies with compound Mef2 isoforms would be required to address this. We also show that Mef2D is highly expressed in the thymus, but that loss of Mef2D does not affect thymic T-cell development or the production of IFNγ from CD8 T cells.

Identifying Inhibitors of Inflammation: A Novel High-Throughput MALDI-TOF Screening Assay for Salt-Inducible Kinases (SIKs).

Matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) mass spectrometry has become a promising alternative for high-throughput drug discovery as new instruments offer high speed, flexibility and sensitivity, and the ability to measure physiological substrates label free. Here we developed and applied high-throughput MALDI TOF mass spectrometry to identify inhibitors of the salt-inducible kinase (SIK) family, which are interesting drug targets in the field of inflammatory disease as they control production of the anti-inflammatory cytokine interleukin-10 (IL-10) in macrophages. Using peptide substrates in in vitro kinase assays, we can show that hit identification of the MALDI TOF kinase assay correlates with indirect ADP-Hunter kinase assays. Moreover, we can show that both techniques generate comparable IC50 data for a number of hit compounds and known inhibitors of SIK kinases. We further take these inhibitors to a fluorescence-based cellular assay using the SIK activity-dependent translocation of CRTC3 into the nucleus, thereby providing a complete assay pipeline for the identification of SIK kinase inhibitors in vitro and in cells. Our data demonstrate that MALDI TOF mass spectrometry is fully applicable to high-throughput kinase screening, providing label-free data comparable to that of current high-throughput fluorescence assays.

MSK1 regulates transcriptional induction of Arc/Arg3.1 in response to neurotrophins.

The immediate early gene activity-regulated cytoskeletal protein (Arc)/Arg3.1 and the neurotrophin brain-derived neurotrophic factor (BDNF) play important roles in synaptic plasticity and learning and memory in the mammalian brain. However, the mechanisms by which BDNF regulates the expression of Arc/Arg3.1 are unclear. In this study, we show that BDNF acts via the ERK1/2 pathway to activate the nuclear kinase mitogen- and stress-activated protein kinase 1 (MSK1). MSK1 then induces Arc/Arg3.1 expression via the phosphorylation of histone H3 at the Arc/Arg3.1 promoter. MSK1 can also phosphorylate the transcription factor cyclic-AMP response element-binding protein (CREB) on Ser133. However, this is not required for BDNF-induced Arc.Arg3.1 transcription as a Ser133Ala knockin mutation had no effect on Arc/Arg3.1 induction. In parallel, ERK1/2 directly activates Arc/Arg3.1 mRNA transcription via at least one serum response element on the promoter, which bind a complex of the Serum Response Factor (SRF) and a Ternary Complex Factor (TCF).

Emerging Roles of the Mitogen and Stress Activated Kinases MSK1 and MSK2.

Mitogen- and stress-activated kinases (MSK) 1 and 2 are nuclear proteins activated downstream of the ERK1/2 or p38 MAPK pathways. MSKs phosphorylate multiple substrates, including CREB and Histone H3, and their major role is the regulation of specific subsets of Immediate Early genes (IEG). While MSKs are expressed in multiple tissues, their levels are high in immune and neuronal cells and it is in these systems most is known about their function. In immunity, MSKs have predominantly anti-inflammatory roles and help regulate production of the anti-inflammatory cytokine IL-10. In the CNS they are implicated in neuronal proliferation and synaptic plasticity. In this review we will focus on recent advances in understanding the roles of MSKs in the innate immune system and neuronal function.

Accelerated apoptotic death and in vivo turnover of erythrocytes in mice lacking functional mitogen- and stress-activated kinase MSK1/2.

The mitogen- and stress-activated kinase MSK1/2 plays a decisive role in apoptosis. In analogy to apoptosis of nucleated cells, suicidal erythrocyte death called eryptosis is characterized by cell shrinkage and cell membrane scrambling leading to phosphatidylserine (PS) externalization. Here, we explored whether MSK1/2 participates in the regulation of eryptosis. To this end, erythrocytes were isolated from mice lacking functional MSK1/2 (msk(-/-)) and corresponding wild-type mice (msk(+/+)). Blood count, hematocrit, hemoglobin concentration and mean erythrocyte volume were similar in both msk(-/-) and msk(+/+) mice, but reticulocyte count was significantly increased in msk(-/-) mice. Cell membrane PS exposure was similar in untreated msk(-/-) and msk(+/+) erythrocytes, but was enhanced by pathophysiological cell stressors ex vivo such as hyperosmotic shock or energy depletion to significantly higher levels in msk(-/-) erythrocytes than in msk(+/+) erythrocytes. Cell shrinkage following hyperosmotic shock and energy depletion, as well as hemolysis following decrease of extracellular osmolarity was more pronounced in msk(-/-) erythrocytes. The in vivo clearance of autologously-infused CFSE-labeled erythrocytes from circulating blood was faster in msk(-/-) mice. The spleens from msk(-/-) mice contained a significantly greater number of PS-exposing erythrocytes than spleens from msk(+/+) mice. The present observations point to accelerated eryptosis and subsequent clearance of erythrocytes leading to enhanced erythrocyte turnover in MSK1/2-deficient mice.

Development of Selective Covalent Janus Kinase 3 Inhibitors.

The Janus kinases (JAKs) and their downstream effectors, signal transducer and activator of transcription proteins (STATs), form a critical immune cell signaling circuit, which is of fundamental importance in innate immunity, inflammation, and hematopoiesis, and dysregulation is frequently observed in immune disease and cancer. The high degree of structural conservation of the JAK ATP binding pockets has posed a considerable challenge to medicinal chemists seeking to develop highly selective inhibitors as pharmacological probes and as clinical drugs. Here we report the discovery and optimization of 2,4-substituted pyrimidines as covalent JAK3 inhibitors that exploit a unique cysteine (Cys909) residue in JAK3. Investigation of structure-activity relationship (SAR) utilizing biochemical and transformed Ba/F3 cellular assays resulted in identification of potent and selective inhibitors such as compounds 9 and 45. A 2.9 Å cocrystal structure of JAK3 in complex with 9 confirms the covalent interaction. Compound 9 exhibited decent pharmacokinetic properties and is suitable for use in vivo. These inhibitors provide a set of useful tools to pharmacologically interrogate JAK3-dependent biology.

HIV protease inhibitors and onset of cardiovascular diseases: a central role for oxidative stress and dysregulation of the ubiquitin-proteasome system.

The successful roll-out of highly active antiretroviral therapy (HAART) has extended life expectancy and enhanced the overall well-being of HIV-positive individuals. There are, however, increased concerns regarding HAART-mediated metabolic derangements and its potential risk for cardiovascular diseases (CVD) in the long-term. Here certain classes of antiretroviral drugs such as the HIV protease inhibitors (PIs) are strongly implicated in this process. This article largely focuses on the direct PI-linked development of cardio-metabolic complications, and reviews the inter-linked roles of oxidative stress and the ubiquitin-proteasome system (UPS) as key mediators driving this process. It is proposed that PIs trigger reactive oxygen species (ROS) production that leads to serious downstream consequences such as cell death, impaired mitochondrial function, and UPS dysregulation. Moreover, we advocate that HIV PIs may also directly lower myocardial UPS function. The attenuation of cardiac UPS can initiate transcriptional changes that contribute to perturbed lipid metabolism, thereby fueling a pro-atherogenic milieu. It may also directly alter ionic channels and interfere with electrical signaling in the myocardium. Therefore HIV PI-induced ROS together with a dysfunctional UPS elicit detrimental effects on the cardiovascular system that will eventually result in the onset of heart diseases. Thus while HIV PIs substantially improve life expectancy and quality of life in HIV-positive patients, its longer-term side-effects on the cardiovascular system should lead to a) greater clinical awareness regarding its benefit-harm paradigm, and b) the development and evaluation of novel co-treatment strategies.

Cardio-metabolic effectsof HIV protease inhibitors (lopinavir/ritonavir).

Although antiretroviral treatment decreases HIV-AIDS morbidity/mortality, long-term side effects may include the onset of insulin resistance and cardiovascular diseases. However, the underlying molecular mechanisms responsible for highly active antiretroviral therapy (HAART)-induced cardio-metabolic effects are poorly understood. In light of this, we hypothesized that HIV protease inhibitor (PI) treatment (Lopinavir/Ritonavir) elevates myocardial oxidative stress and concomitantly inhibits the ubiquitin proteasome system (UPS), thereby attenuating cardiac function. Lopinavir/Ritonavir was dissolved in 1% ethanol (vehicle) and injected into mini-osmotic pumps that were surgically implanted into Wistar rats for 8 weeks vs. vehicle and sham controls. We subsequently evaluated metabolic parameters, gene/protein markers and heart function (ex vivo Langendorff perfusions). PI-treated rats exhibited increased serum LDL-cholesterol, higher tissue triglycerides (heart, liver), but no evidence of insulin resistance. In parallel, there was upregulation of hepatic gene expression, i.e. acetyl-CoA carboxylase b and 3-hydroxy-3-methylglutaryl-CoA-reductase, key regulators of fatty acid oxidation and cholesterol synthesis, respectively. PI-treated hearts displayed impaired cardiac contractile function together with attenuated UPS activity. However, there was no significant remodeling of hearts exposed to PIs, i.e. lack of ultrastructural changes, fibrosis, cardiac hypertrophic response, and oxidative stress. Western blot analysis of PI-treated hearts revealed that perturbed calcium handling may contribute to the PI-mediated contractile dysfunction. Here chronic PI administration led to elevated myocardial calcineurin, nuclear factor of activated T-cells 3 (NFAT3), connexin 43, and phosphorylated phospholamban, together with decreased calmodulin expression levels. This study demonstrates that early changes triggered by PI treatment include increased serum LDL-cholesterol levels together with attenuated cardiac function. Furthermore, PI exposure inhibits the myocardial UPS and leads to elevated calcineurin and connexin 43 expression that may be associated with the future onset of cardiac contractile dysfunction.