Phosphoproteomic analysis reveals CDK5-Mediated phosphorylation of MTDH inhibits protein synthesis in microglia

CDK5 plays a crucial role in maintaining normal central nervous system (CNS) development and synaptic function, while microglia are the primary immune cells present in the CNS and play vital physiological roles in CNS development, immune surveillance, and regulation of synaptic plasticity. Despite this, our understanding of both the substrate proteins and functional mechanisms of CDK5 in microglia remains limited. To address this, we utilized CRISPR-Cas9 knockout of Cdk5 in BV2 cells and conducted quantitative phosphoproteomics analysis to systematically screen potential CDK5 substrates in microglia. Our findings identified 335 phosphorylation sites on 234 proteins as potential CDK5 substrates in microglia based on the reported sequence motif. Through in vitro kinase assay and intracellular inhibition and knockout of CDK5 experiments, we confirmed that ER proteins MTDH (protein LYRIC) and Calnexin are novel substrate proteins of CDK5. Moreover, we demonstrated for the first time a critical mechanism for regulating protein synthesis in microglia, that the phosphorylation of S565 site on MTDH, a key protein mediating cell growth, by CDK5 inhibits protein synthesis. Our data provide valuable insights for the discovery of new substrate proteins of CDK5 and the in-depth investigation of the function and mechanism of CDK5 in microglia.

Regulation of Microtubule Stability in Pulmonary Microvascular Endothelial Cells in Rats with Severe Acute Pancreatitis: Qingyi Decoction is a Potential CDK5 Inhibitor

Purpose

Explore the therapeutic effects and regulatory mechanism of Qingyi Decoction (QYD) on severe acute pancreatitis (SAP) associated acute lung injury (ALI).

Methods

We identified the constituents absorbed into the blood of QYD based on a network pharmacological strategy. The differentially expressed genes from the GEO database were screened to identify the critical targets of QYD treatment of SAP-ALI. The SAP-ALI rat model was constructed.Some methods were used to evaluate the efficacy and mechanism of QYD in treating SAP-ALI. LPS-stimulated pulmonary microvascular endothelial cell injury simulated the SAP-induced pulmonary endothelial injury model. We further observed the therapeutic effect of QYD and CDK5 plasmid transfection on endothelial cell injury.

Results

18 constituents were absorbed into the blood, and 764 targets were identified from QYD, 25 of which were considered core targets for treating SAP-ALI. CDK5 was identified as the most critical gene. The results of differential expression analysis showed that the mRNA expression level of CDK5 in the blood of SAP patients was significantly up-regulated compared with that of healthy people. Animal experiments have demonstrated that QYD can alleviate pancreatic and lung injury inflammatory response and reduce the upregulation of CDK5 in lung tissue. QYD or CDK5 inhibitors could decrease the expression of NFAT5 and GEF-H1, and increase the expression of ACE-tub in SAP rat lung tissue. Cell experiments proved that QYD could inhibit the expression of TNF-α and IL-6 induced by LPS. Immunofluorescence results suggested that QYD could alleviate the cytoskeleton damage of endothelial cells, and the mechanism might be related to the inhibition of CDK5-mediated activation of NFAT5, GEF-H1, and ACE-tub.

Conclusion

CDK5 has been identified as a critical target for pulmonary endothelial injury of SAP-ALI. QYD may partially alleviate microtubule disassembly by targeting the CDK5/NFAT5/GEF-H1 signaling pathway, thus relieving SAP-induced pulmonary microvascular endothelial cell injury.

p35 is a Crucial Player in NK-cell Cytotoxicity and TGFβ-mediated NK-cell Dysfunction

Natural killer (NK) cells are innate lymphocytes with cytotoxic activity. Understanding the factors regulating cytotoxicity is crucial for improving NK-cell adoptive therapies. Here, we studied a previously unknown role of p35 (CDK5R1), a coactivator of cyclin-dependent kinase 5 (CDK5) in NK-cell function. p35 expression was thought to be neuronal-specific and the majority of studies are still focused on neuronal cells. Here, we show that CDK5 and p35 are expressed in NK cells and are kinase-active. NK cells from p35 knockout mice were analyzed and showed significantly increased cytotoxicity against murine cancer cells, while they did not show any differences in cell numbers or maturation stages. We confirmed this using human NK cells transduced with p35 short hairpin RNA (shRNA), showing similar increase in cytotoxicity against human cancer cells. Overexpression of p35 in NK cells resulted in moderate decrease in cytotoxicity, while expressing a kinase-dead mutant of CDK5 displayed increased cytotoxicity. Together, these data suggest that p35 negatively regulates NK-cell cytotoxicity. Surprisingly, we found that TGFβ, a known negative regulator of NK-cell cytotoxicity, induces p35 expression in NK cells. NK cells cultured with TGFβ exhibit reduced cytotoxicity, while NK cells transduced with p35 shRNA or mutant CDK5 expression exhibited partial reversal of this inhibitory effect pointing to an interesting hypothesis that p35 plays an important role in TGFβ-mediated NK-cell exhaustion.

Significance

This study reports a role for p35 in NK-cell cytotoxicity and this might help to improve NK-cell adoptive therapy.

A novel CDK8 inhibitor with poly-substituted pyridine core: Discovery and anti-inflammatory activity evaluation in vivo

As an ideal anti-inflammatory target, cyclin-dependent kinase 8 (CDK8) has gradually attracted the attention of researchers. CDK8 inhibition up-regulates Interleukin-10 (IL-10) expression by enhancing the transcriptional activity of activator protein-1 (AP-1), and augmenting IL-10 abundance is a viable strategy for the treatment of inflammatory bowel disease (IBD). In this research, through structure-based drug design and dominant fragment hybridization, a series of poly-substituted pyridine derivatives were designed and synthesized as CDK8 inhibitors. Ultimately, compound CR16 was identified as the best one, which exhibited good inhibitory activity against CDK8 (IC₅₀ = 74.4 nM). In vitro and in vivo studies indicated that CR16 could enhance the transcriptional activity of AP-1, augment the abundance of IL-10, and affect CDK8-related signaling pathways including TLR7/NF-κB/MAPK and IL-10-JAK1-STAT3 pathways. In addition, CR16 showed potent therapeutic effect in an animal model of IBD.

SMTP-44D Inhibits Atherosclerotic Plaque Formation in Apolipoprotein-E Null Mice Partly by Suppressing the AGEs-RAGE Axis

SMTP-44D has been reported to have anti-oxidative and anti-inflammatory reactions, including reduced expression of receptor for advanced glycation end products (RAGE) in experimental diabetic neuropathy. Although activation of RAGE with its ligands, and advanced glycation end products (AGEs), play a crucial role in atherosclerotic cardiovascular disease, a leading cause of death in diabetic patients, it remains unclear whether SMTP-44D could inhibit experimental atherosclerosis by suppressing the AGEs–RAGE axis. In this study, we investigated the effects of SMTP-44D on atherosclerotic plaque formation and expression of AGEs in apolipoprotein-E null (Apoe−/−) mice. We further studied here whether and how SMTP-44D inhibited foam cell formation of macrophages isolated from Apoe−/− mice ex vivo. Although administration of SMTP-44D to Apoe−/− mice did not affect clinical or biochemical parameters, it significantly decreased the surface area of atherosclerotic lesions and reduced the atheromatous plaque size, macrophage infiltration, and AGEs accumulation in the aortic roots. SMTP-44D bound to immobilized RAGE and subsequently attenuated the interaction of AGEs with RAGE in vitro. Furthermore, foam cell formation evaluated by Dil-oxidized low-density lipoprotein (ox-LDL) uptake, and gene expression of RAGE, cyclin-dependent kinase 5 (Cdk5) and CD36 in macrophages isolated from SMTP-44D-treated Apoe−/− mice were significantly decreased compared with those from saline-treated mice. Gene expression levels of RAGE and Cdk5 were highly correlated with each other, the latter of which was also positively associated with that of CD36. The present study suggests that SMTP-44D may inhibit atherosclerotic plaque formation in Apoe−/− mice partly by blocking the AGEs-RAGE-induced ox-LDL uptake into macrophages via the suppression of Cdk5-CD36 pathway.

A network biology approach to identify crucial host targets for COVID-19

The ongoing global pandemic of COVID-19, caused by SARS-CoV-2 has killed more than 5.9 million individuals out of ∼43 million confirmed infections. At present, several parts of the world are encountering the 3rd wave. Mass vaccination has been started in several countries but they are less likely to be broadly available for the current pandemic, repurposing of the existing drugs has drawn highest attention for an immediate solution. A recent publication has mapped the physical interactions of SARS-CoV-2 and human proteins by affinity-purification mass spectrometry (AP-MS) and identified 332 high-confidence SARS-CoV-2-human protein-protein interactions (PPIs). Here, we taken a network biology approach and constructed a human protein-protein interaction network (PPIN) with the above SARS-CoV-2 targeted proteins. We utilized a combination of essential network centrality measures and functional properties of the human proteins to identify the critical human targets of SARS-CoV-2. Four human proteins, namely PRKACA, RHOA, CDK5RAP2, and CEP250 have emerged as the best therapeutic targets, of which PRKACA and CEP250 were also found by another group as potential candidates for drug targets in COVID-19. We further found candidate drugs/compounds, such as guanosine triphosphate, remdesivir, adenosine monophosphate, MgATP, and H-89 dihydrochloride that bind the target human proteins. The urgency to prevent the spread of infection and the death of diseased individuals has prompted the search for agents from the pool of approved drugs to repurpose them for COVID-19. Our results indicate that host targeting therapy with the repurposed drugs may be a useful strategy for the treatment of SARS-CoV-2 infection.

Cyclin-dependent kinase 5 inhibitor attenuates lipopolysaccharide-induced neuroinflammation through metabolic reprogramming

The atypical cyclin-dependent kinase 5 (CDK5) is considered a neuron-specific kinase that plays important roles in many cellular functions including neuronal migration, neuronal differentiation, synapse development, and synaptic functions. However, the role of CDK5 in microglia under physiological and pathological conditions remains unclear. This study showed that treatment with lipopolysaccharide (LPS) caused the release of pro-inflammatory mediators and increased expression of CDK5 in BV2 microglia in vitro. Moreover, lipopolysaccharide treatment-induced glycolysis by increasing the expression levels of HIF-1α, PFKFB3, and HK2. Application of CDK5 inhibitor roscovitine significantly decreased LPS-induced CDK5 expression and glycolysis, thus suppressing neuroinflammation in the cells. The roscovitine treatment of BV2 cells also significantly blocked the HIF-1 activator, CoCl₂-mediated HIF-1α, HK2, and PFKFB3 expression. Finally, we demonstrated that roscovitine inhibited microglial activation, metabolic reprogramming, expression of pro-inflammatory markers, cell apoptosis, and alleviated memory impairment in LPS-injected mice. In summary, our results suggest that inhibition of CDK5 can reduce the neuroinflammation of microglia through modulation of metabolic reprogramming.

Roles for macrophage-polarizing interleukins in cancer immunity and immunotherapy

Macrophages are the most abundant and one of the most critical cells of tumor immunity. They provide a bridge between innate and adaptive immunity through releasing cytokines into the tumor microenvironment (TME). A number of interleukin (IL) cytokine family members is involved in shaping the final phenotype of macrophages toward either a classically-activated pro-inflammatory M1 state with anti-tumor activity or an alternatively-activated anti-inflammatory M2 state with pro-tumor activity. Shaping TME macrophages toward the M1 phenotype or recovering this phenotypic state may offer a promising therapeutic approach in patients with cancer. Here, we focus on the impact of macrophage-polarizing ILs on immune cells and IL-mediated cellular cross-interactions within the TME. The key aim of this review is to define therapeutic schedules for addressing ILs in cancer immunotherapy based on their multi-directional impacts in such a milieu. Gathering more knowledge on this area is also important for defining adverse effects related to cytokine therapy and addressing them for reinforcing the efficacy of immunotherapy against cancer.

Endophenotype-based in silico network medicine discovery combined with insurance record data mining identifies sildenafil as a candidate drug for Alzheimer's disease

We developed an endophenotype disease module-based methodology for Alzheimer's disease (AD) drug repurposing and identified sildenafil as a potential disease risk modifier. Based on retrospective case-control pharmacoepidemiologic analyses of insurance claims data for 7.23 million individuals, we found that sildenafil usage was significantly associated with a 69% reduced risk of AD (hazard ratio = 0.31, 95% confidence interval 0.25-0.39, P<1.0×10^-8). Propensity score stratified analyses confirmed that sildenafil is significantly associated with a decreased risk of AD across all four drug cohorts we tested (diltiazem, glimepiride, losartan and metformin) after adjusting age, sex, race, and disease comorbidities. We also found that sildenafil increases neurite growth and decreases phospho-tau expression in AD patient-induced pluripotent stem cells-derived neuron models, supporting mechanistically its potential beneficial effect in Alzheimer's disease. The association between sildenafil use and decreased incidence of AD does not establish causality or its direction, which requires a randomized clinical trial approach.

Protocols for Characterization of Cdk5 Kinase Activity

Cyclin-dependent kinases (Cdks) are generally known to be involved in controlling the cell cycle, but Cdk5 is a unique member of this protein family for being most active in post-mitotic neurons. Cdk5 is developmentally important in regulating neuronal migration, neurite outgrowth, and axon guidance. Cdk5 is enriched in synaptic membranes and is known to modulate synaptic activity. Postnatally, Cdk5 can also affect neuronal processes such as dopaminergic signaling and pain sensitivity. Dysregulated Cdk5, in contrast, has been linked to neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). Despite primarily being implicated in neuronal development and activity, Cdk5 has lately been linked to non-neuronal functions including cancer cell growth, immune responses, and diabetes. Since Cdk5 activity is tightly regulated, a method for measuring its kinase activity is needed to fully understand the precise role of Cdk5 in developmental and disease processes. This article includes methods for detecting Cdk5 kinase activity in cultured cells or tissues, identifying new substrates, and screening for new kinase inhibitors. Furthermore, since Cdk5 shares homology and substrate specificity with Cdk1 and Cdk2, the Cdk5 kinase assay can be used, with modification, to measure the activity of other Cdks as well. © 2021 Wiley Periodicals LLC. This article has been contributed to by US Government employees and their work is in the public domain in the USA. Basic Protocol 1: Measuring Cdk5 activity from protein lysates Support Protocol 1: Immunoprecipitation of Cdk5 using Dynabeads Alternate Protocol: Non-radioactive protocols to measure Cdk5 kinase activity Support Protocol 2: Western blot analysis for the detection of Cdk5, p35, and p39 Support Protocol 3: Immunodetection analysis for Cdk5, p35, and p39 Support Protocol 4: Genetically engineered mice (+ and - controls) Basic Protocol 2: Identifying new Cdk5 substrates and kinase inhibitors.

Multimodal single-cell/nucleus RNA sequencing data analysis uncovers molecular networks between disease-associated microglia and astrocytes with implications for drug repurposing in Alzheimer's disease

Because disease-associated microglia (DAM) and disease-associated astrocytes (DAA) are involved in the pathophysiology of Alzheimer's disease (AD), we systematically identified molecular networks between DAM and DAA to uncover novel therapeutic targets for AD. Specifically, we develop a network-based methodology that leverages single-cell/nucleus RNA sequencing data from both transgenic mouse models and AD patient brains, as well as drug-target network, metabolite-enzyme associations, the human protein-protein interactome, and large-scale longitudinal patient data. Through this approach, we find both common and unique gene network regulators between DAM (i.e., PAK1, MAPK14, and CSF1R) and DAA (i.e., NFKB1, FOS, and JUN) that are significantly enriched by neuro-inflammatory pathways and well-known genetic variants (i.e., BIN1). We identify shared immune pathways between DAM and DAA, including Th17 cell differentiation and chemokine signaling. Last, integrative metabolite-enzyme network analyses suggest that fatty acids and amino acids may trigger molecular alterations in DAM and DAA. Combining network-based prediction and retrospective case-control observations with 7.2 million individuals, we identify that usage of fluticasone (an approved glucocorticoid receptor agonist) is significantly associated with a reduced incidence of AD (hazard ratio [HR] = 0.86, 95% confidence interval [CI] 0.83-0.89, P < 1.0 × 10-8). Propensity score-stratified cohort studies reveal that usage of mometasone (a stronger glucocorticoid receptor agonist) is significantly associated with a decreased risk of AD (HR = 0.74, 95% CI 0.68-0.81, P < 1.0 × 10-8) compared to fluticasone after adjusting age, gender, and disease comorbidities. In summary, we present a network-based, multimodal methodology for single-cell/nucleus genomics-informed drug discovery and have identified fluticasone and mometasone as potential treatments in AD.

Deletion of Cdk5 in Macrophages Ameliorates Anti-Inflammatory Response during Endotoxemia through Induction of C-Maf and Il-10

Immune response control is critical as excessive cytokine production can be detrimental and damage the host. Interleukin-10 (Il-10), an anti-inflammatory cytokine produced primarily by macrophages, is a key regulator that counteracts and controls excessive inflammatory response. Il-10 expression is regulated through the transcription factor c-Maf. Another regulator of Il-10 production is p35, an activator of the cyclin-dependent kinase 5 (Cdk5), which decreases Il-10 production in macrophages, thus increasing inflammation. However, Cdk5 regulation of c-Maf and the involvement of Il-10 production in macrophages has not yet been investigated. We used in vitro primary bone marrow-derived macrophages (BMDMs) lacking Cdk5, stimulated them with lipopolysaccharid (LPS) and observed increased levels of c-Maf and Il-10. In an in vivo mouse model of LPS-induced endotoxemia, mice lacking Cdk5 in macrophages showed increased levels of c-Maf and elevated levels of Il-10 in lungs as well as in plasma, resulting in ameliorated survival. Taken together, we identified Cdk5 as a potential novel regulator of Il-10 production through c-Maf in macrophages under inflammatory conditions. Our results suggest that inhibition of Cdk5 enhances the c-Maf-Il-10 axis and thus potentiates improvement of anti-inflammatory therapy.

Neuropathological Effects of Chemotherapeutic Drugs

Novel treatments, screening, and detection methods have prolonged the lives of numerous cancer patients worldwide. Unfortunately, existing and many promising new chemotherapeutics can cause deleterious, off-target side effects in normal tissue and organ systems. The central and peripheral nervous systems are widely recognized as frequent off-target effectors of anticancer drugs which can produce persistent neurological and neuropsychiatric symptoms collectively termed "chemobrain". Following chemotherapy, patients report several forms of cognitive impairment occurring acutely and sometimes persisting years after treatment. There are no effective treatments for cognitive decline induced by chemotherapeutics, and the underlying molecular mechanisms are poorly characterized and understood. In this study, we find that chronic treatment with two common chemotherapeutic agents, cisplatin and gemcitabine, impairs brain region-specific metabolism, hippocampus-dependent memory formation, and stress response behavior. This corresponds to reduced hippocampal synaptic excitability, altered neuronal signal transduction, and neuroinflammation. These findings underline that a better understanding of the basic pathological consequences of chemotherapy-induced cognitive impairment is the first step toward improving cancer treatment survivorship.

Glucose-Dependent Insulinotropic Polypeptide Suppresses Foam Cell Formation of Macrophages through Inhibition of the Cyclin-Dependent Kinase 5-CD36 Pathway

Glucose-dependent insulinotropic polypeptide (GIP) has been reported to have an atheroprotective property in animal models. However, the effect of GIP on macrophage foam cell formation, a crucial step of atherosclerosis, remains largely unknown. We investigated the effects of GIP on foam cell formation of, and CD36 expression in, macrophages extracted from GIP receptor-deficient (Gipr^−/−) and Gipr^+/+ mice and cultured human U937 macrophages by using an agonist for GIP receptor, [D-Ala²]GIP(1–42). Foam cell formation evaluated by esterification of free cholesterol to cholesteryl ester and CD36 gene expression in macrophages isolated from Gipr^+/+ mice infused subcutaneously with [D-Ala²]GIP(1–42) were significantly suppressed compared with vehicle-treated mice, while these beneficial effects were not observed in macrophages isolated from Gipr^−/− mice infused with [D-Ala²]GIP(1–42). When macrophages were isolated from Gipr^+/+ and Gipr^−/− mice, and then exposed to [D-Ala²]GIP(1–42), similar results were obtained. [D-Ala²]GIP(1–42) attenuated ox-LDL uptake of, and CD36 gene expression in, human U937 macrophages as well. Gene expression level of cyclin-dependent kinase 5 (Cdk5) was also suppressed by [D-Ala²]GIP(1–42) in U937 cells, which was corelated with that of CD36. A selective inhibitor of Cdk5, (R)-DRF053 mimicked the effects of [D-Ala²]GIP(1–42) in U937 cells. The present study suggests that GIP could inhibit foam cell formation of macrophages by suppressing the Cdk5-CD36 pathway via GIP receptor.

Cellular and Molecular Mechanisms of R/S-Roscovitine and CDKs Related Inhibition under Both Focal and Global Cerebral Ischemia: A Focus on Neurovascular Unit and Immune Cells

Ischemic stroke is the second leading cause of death worldwide. Following ischemic stroke, Neurovascular Unit (NVU) inflammation and peripheral leucocytes infiltration are major contributors to the extension of brain lesions. For a long time restricted to neurons, the 10 past years have shown the emergence of an increasing number of studies focusing on the role of Cyclin-Dependent Kinases (CDKs) on the other cells of NVU, as well as on the leucocytes. The most widely used CDKs inhibitor, (R)-roscovitine, and its (S) isomer both decreased brain lesions in models of global and focal cerebral ischemia. We previously showed that (S)-roscovitine acted, at least, by modulating NVU response to ischemia. Interestingly, roscovitine was shown to decrease leucocytes-mediated inflammation in several inflammatory models. Specific inhibition of roscovitine majors target CDK 1, 2, 5, 7, and 9 showed that these CDKs played key roles in inflammatory processes of NVU cells and leucocytes after brain lesions, including ischemic stroke. The data summarized here support the investigation of roscovitine as a potential therapeutic agent for the treatment of ischemic stroke, and provide an overview of CDK 1, 2, 5, 7, and 9 functions in brain cells and leucocytes during cerebral ischemia.

AGE-RAGE Axis Stimulates Oxidized LDL Uptake into Macrophages through Cyclin-Dependent Kinase 5-CD36 Pathway via Oxidative Stress Generation

Advanced glycation end products (AGEs) are localized in macrophage-derived foam cells within atherosclerotic lesions, which could be associated with the increased risk of atherosclerotic cardiovascular disease under diabetic conditions. Although foam cell formation of macrophages has been shown to be enhanced by AGEs, the underlying molecular mechanism remains unclear. Since cyclin-dependent kinase 5 (Cdk5) is reported to modulate inflammatory responses in macrophages, we investigated whether Cdk5 could be involved in AGE-induced CD36 gene expression and foam cell formation of macrophages. AGEs significantly increased Dil-oxidized low-density lipoprotein (ox-LDL) uptake, and Cdk5 and CD36 gene expression in U937 human macrophages, all of which were inhibited by DNA aptamer raised against RAGE (RAGE-aptamer). Cdk5 and CD36 gene expression levels were correlated with each other. An antioxidant, N-acetyl-l-cysteine, mimicked the effects of RAGE-aptamer on AGE-exposed U937 cells. A selective inhibitor of Cdk5, (R)-DRF053, attenuated the AGE-induced Dil-ox-LDL uptake and CD36 gene expression, whereas anti-CD36 antibody inhibited the Dil-ox-LDL uptake but not Cdk5 gene expression. The present study suggests that AGEs may stimulate ox-LDL uptake into macrophages through the Cdk5–CD36 pathway via RAGE-mediated oxidative stress.

A kinase of many talents: non-neuronal functions of CDK5 in development and disease

The cyclin-dependent kinase 5 (CDK5) represents an unusual member of the family of cyclin-dependent kinases, which is activated upon binding to non-cyclin p35 and p39 proteins. The role of CDK5 in the nervous system has been very well established. In addition, there is growing evidence that CDK5 is also active in non-neuronal tissues, where it has been postulated to affect a variety of functions such as the immune response, angiogenesis, myogenesis, melanogenesis and regulation of insulin levels. Moreover, high levels of CDK5 have been observed in different tumour types, and CDK5 was proposed to play various roles in the tumorigenic process. In this review, we discuss these various CDK5 functions in normal physiology and disease, and highlight the therapeutic potential of targeting CDK5.

Cdk5 Deletion Enhances the Anti-inflammatory Potential of GC-Mediated GR Activation During Inflammation

The suppression of activated pro-inflammatory macrophages during immune response has a major impact on the outcome of many inflammatory diseases including sepsis and rheumatoid arthritis. The pro- and anti-inflammatory functions of macrophages have been widely studied, whereas their regulation under immunosuppressive treatments such as glucocorticoid (GC) therapy is less well-understood. GC-mediated glucocorticoid receptor (GR) activation is crucial to mediate anti-inflammatory effects. In addition, the anti-cancer drug roscovitine, that is currently being tested in clinical trials, was recently described to regulate inflammatory processes by inhibiting different Cdks such as cyclin-dependent kinase 5 (Cdk5). Cdk5 was identified as a modulator of inflammatory processes in different immune cells and furthermore described to influence GR gene expression in the brain. Whether roscovitine can enhance the immunosuppressive effects of GCs and if the inhibition of Cdk5 affects GR gene regulatory function in innate immune cells, such as macrophages, has not yet been investigated. Here, we report that roscovitine enhances the immunosuppressive Dexamethasone (Dex) effect on the inducible nitric oxide synthase (iNos) expression, which is essential for immune regulation. Cdk5 deletion in macrophages prevented iNos protein and nitric oxide (NO) generation after a combinatory treatment with inflammatory stimuli and Dex. Cdk5 deletion in macrophages attenuated the GR phosphorylation on serine 211 after Dex treatment alone and in combination with inflammatory stimuli, but interestingly increased the GR-dependent anti-inflammatory target gene dual-specificity phosphatase 1 (Dusp1, Mkp1). Mkp1 phosphatase activity decreases the activation of its direct target p38Mapk, reduced iNos expression and NO production upon inflammatory stimuli and Dex treatment in the absence of Cdk5. Taken together, we identified Cdk5 as a potential novel regulator of NO generation in inflammatory macrophages under GC treatment. Our data suggest that GC treatment in combination with specific Cdk5 inhibtior(s) provides a stronger suppression of inflammation and could thus replace high-dose GC therapy which has severe side effects in the treatment of inflammatory diseases.

The Post-amyloid Era in Alzheimer's Disease: Trust Your Gut Feeling

The amyloid hypothesis, the assumption that beta-amyloid toxicity is the primary cause of neuronal and synaptic loss, has been the mainstream research concept in Alzheimer's disease for the past two decades. Currently, this model is quietly being replaced by a more holistic, “systemic disease” paradigm which, like the aging process, affects multiple body tissues and organs, including the gut microbiota. It is well-established that inflammation is a hallmark of cellular senescence; however, the infection-senescence link has been less explored. Microbiota-induced senescence is a gradually emerging concept promoted by the discovery of pathogens and their products in Alzheimer's disease brains associated with senescent neurons, glia, and endothelial cells. Infectious agents have previously been associated with Alzheimer's disease, but the cause vs. effect issue could not be resolved. A recent study may have settled this debate as it shows that gingipain, a Porphyromonas gingivalis toxin, can be detected not only in Alzheimer's disease but also in the brains of older individuals deceased prior to developing the illness. In this review, we take the position that gut and other microbes from the body periphery reach the brain by triggering intestinal and blood-brain barrier senescence and disruption. We also surmise that novel Alzheimer's disease findings, including neuronal somatic mosaicism, iron dyshomeostasis, aggressive glial phenotypes, and loss of aerobic glycolysis, can be explained by the infection-senescence model. In addition, we discuss potential cellular senescence targets and therapeutic strategies, including iron chelators, inflammasome inhibitors, senolytic antibiotics, mitophagy inducers, and epigenetic metabolic reprograming.

Aryl Hydrocarbon Receptor Promotes IL-10 Expression in Inflammatory Macrophages Through Src-STAT3 Signaling Pathway

The aryl hydrocarbon receptor (AhR) is an important immune regulator with a role in inflammatory response. However, the role of AhR in IL-10 production by inflammatory macrophages is currently unknown. In this study, we investigated LPS-induced IL-10 expression in macrophages from AhR-KO mice and AhR-overexpressing RAW264.7 cells. AhR was highly expressed after LPS stimulation through NF-κB pathway. Loss of AhR resulted in reduced IL-10 expression in LPS-induced macrophages. Moreover, the IL-10 expression was elevated in LPS-induced AhR-overexpressing RAW264.7 cells. Maximal IL-10 expression was dependent on an AhR non-genomic pathway closely related to Src and STAT3. Furthermore, AhR-associated Src activity was responsible for tyrosine phosphorylation of STAT3 and IL-10 expression by inflammatory macrophages. Adoptive transfer of AhR-expressing macrophages protected mice against LPS-induced peritonitis associated with high IL-10 production. In conclusion, we identified the AhR-Src-STAT3-IL-10 signaling pathway as a critical pathway in the immune regulation of inflammatory macrophages, It suggests that AhR may be a potential therapeutic target in immune response.

Electro-Acupuncture at Zusanli Acupoint (ST36) Suppresses Inflammation in Allergic Contact Dermatitis Via Triggering Local IL-10 Production and Inhibiting p38 MAPK Activation

Acupuncture has shown beneficial effect in the treatment of multiple dermatologic conditions including dermatitis, pruritus, urticaria, and hyperhidrosis; however, the detailed mechanisms are still kept unclear. This study aimed to investigate if electro-acupuncture (EA) treatment prevents 2,4-dinitrofluorobenzene (DNFB)-induced allergic contact dermatitis (ACD) in rats and explore its underlying mechanisms. ACD was induced by sensitizing and challenging with DNFB topically. Rats were treated daily following bilateral subcutaneous stimulation of EA at Zusanli acupoint (ST36) for 1 week. Ear swelling and serum IgE levels were measured. The ear biopsies were obtained for histology. Inflammatory cytokines on the dermatological ear and local acupoint tissue were assayed. Spleen lymphocytes and the homogenized supernatant of local acupuncture area were used to co-culture for flow cytology and immune analysis, respectively. EA treatment at ST36 notably inhibited ear swelling and inflammatory cell infiltration on DNFB-induced ACD. EA also decreased serum IgE concentrations and alleviated the production of inflammatory cytokines in dermatological ear. Additionally, EA treatment attenuated the percentage of CD4⁺IFN-γ⁺ and CD4⁺IL-4⁺ T cells associated with ACD. Interestingly, secretion of interleukin (IL)-10 in the local acupoint tissue following EA stimulation was increased and showed suppressive function when co-cultured with the spleen lymphocytes from DNFB group. Lastly, EA treatment demonstrably suppressed p38 MAPK activation in DNFB-treated rats. Our findings suggest that EA treatment at ST36 may ameliorate inflammation associated with DNFB-induced ACD via triggering local IL-10 production and inhibiting p38 MAPK activation, which provide an alternative and promising therapy for ACD.

CDK5 in oncology: recent advances and future prospects

Selective abrogation of cyclin-dependent kinases (CDK) activity is a highly promising strategy in cancer treatment. The atypical CDK, CDK5 has long been known for its role in neurodegenerative diseases, and is becoming an attractive drug target for cancer therapy. Myriads of recent studies have uncovered that aberrant expression of CDK5 contributes to the oncogenic initiation and progression of multiple solid and hematological malignancies. CDK5 is also implicated in the regulation of cancer stem cell biology. In this review, we present the current state of knowledge of CDK5 as a druggable target for cancer treatment. We also provide a detailed outlook of designing selective and potent inhibitors of this enzyme.

Three-dimensional structural analysis reveals a Cdk5-mediated kinase cascade regulating hepatic biliary network branching in zebrafish

The intrahepatic biliary network is a highly branched three-dimensional network lined by biliary epithelial cells, but how its branching patterns are precisely established is not clear. We designed a new computer-based algorithm that quantitatively computes the structural differences of the three-dimensional networks. Utilizing the algorithm, we showed that inhibition of Cyclin-dependent kinase 5 (Cdk5) led to reduced branching in the intrahepatic biliary network in zebrafish. Further, we identified a previously unappreciated downstream kinase cascade regulated by Cdk5. Pharmacological manipulations of this downstream kinase cascade produced a crowded branching defect in the intrahepatic biliary network and influenced actin dynamics in biliary epithelial cells. We generated larvae carrying a mutation in cdk5 regulatory subunit 1a (cdk5r1a), an essential activator of Cdk5. cdk5r1a mutant larvae show similar branching defects as those observed in Cdk5 inhibitor-treated larvae. A small-molecule compound that interferes with the downstream kinase cascade rescued the mutant phenotype. These results provide new insights into branching morphogenesis of the intrahepatic biliary network.

Small-molecule studies identify CDK8 as a regulator of IL-10 in myeloid cells

Enhancing production of the anti-inflammatory cytokine interleukin-10 (IL-10) is a promising strategy to suppress pathogenic inflammation. To identify new mechanisms regulating IL-10 production, we conducted a phenotypic screen for small molecules that enhance IL-10 secretion from activated dendritic cells. Mechanism-of-action studies using a prioritized hit from the screen, BRD6989, identified the Mediator-associated kinase CDK8, and its paralog CDK19, as negative regulators of IL-10 production during innate immune activation. The ability of BRD6989 to upregulate IL-10 is recapitulated by multiple, structurally differentiated CDK8 and CDK19 inhibitors and requires an intact cyclin C-CDK8 complex. Using a highly parallel pathway reporter assay, we identified a role for enhanced AP-1 activity in IL-10 potentiation following CDK8 and CDK19 inhibition, an effect associated with reduced phosphorylation of a negative regulatory site on c-Jun. These findings identify a function for CDK8 and CDK19 in regulating innate immune activation and suggest that these kinases may warrant consideration as therapeutic targets for inflammatory disorders.

Cyclin-dependent kinase 5 activity is required for allogeneic T-cell responses after hematopoietic cell transplantation in mice

Molecular intermediates in T-cell activation pathways are crucial targets for the therapy and prevention of graft-versus-host disease (GVHD) following allogeneic hematopoietic cell transplantation (allo-HCT). We recently identified an essential role for cyclin-dependent kinase 5 (Cdk5) in T-cell activation and effector function, but the contribution of Cdk5 activity to the development of GVHD has not been explored. Using an established, preclinical, murine, GVHD model, we reveal that Cdk5 activity is increased in key target organs early after allo-HCT. We then generated chimeric mice (Cdk5^+/+C or Cdk5^-/-C) using hematopoietic progenitors from either embryonic day 16.5 Cdk5^+/+ or Cdk5^-/- embryos to enable analyses of the role of Cdk5 in GVHD, as germ line Cdk5 gene deletion is embryonically lethal. The immunophenotype of adult Cdk5^-/-C mice is identical to control Cdk5^+/+C mice. However, transplantation of donor Cdk5^-/-C bone marrow and T cells dramatically reduced the severity of systemic and target organ GVHD. This phenotype is attributed to decreased T-cell migration to secondary lymphoid organs (SLOs), reduced in vivo proliferation within these organs, and fewer cytokine-producing donor T cells during GVHD development. Moreover, these defects in Cdk5^-/- T-cell function are associated with altered CCR7 signaling following ligation by CCL19, a receptor:ligand interaction critical for T-cell migration into SLOs. Although Cdk5 activity in donor T cells contributed to graft-versus-tumor effects, pharmacologic inhibition of Cdk5 preserved leukemia-free survival. Collectively, our data implicate Cdk5 in allogeneic T-cell responses after HCT and as an important new target for therapeutic intervention.

Experimental approaches for investigation of aminoacyl tRNA synthetase phosphorylation

Phosphorylation of many aminoacyl tRNA synthetases (AARSs) has been recognized for decades, but the contribution of post-translational modification to their primary role in tRNA charging and decryption of genetic code remains unclear. In contrast, phosphorylation is essential for performance of diverse noncanonical functions of AARSs unrelated to protein synthesis. Phosphorylation of glutamyl-prolyl tRNA synthetase (EPRS) has been investigated extensively in our laboratory for more than a decade, and has served as an archetype for studies of other AARSs. EPRS is a constituent of the IFN-γ-activated inhibitor of translation (GAIT) complex that directs transcript-selective translational control in myeloid cells. Stimulus-dependent phosphorylation of EPRS is essential for its release from the parental multi-aminoacyl tRNA synthetase complex (MSC), for binding to other GAIT complex proteins, and for regulating the binding to target mRNAs. Importantly, phosphorylation is the common driving force for the context- and stimulus-dependent release, and non-canonical activity, of other AARSs residing in the MSC, for example, lysyl tRNA synthetase (KARS). Here, we describe the concepts and experimental methodologies we have used to investigate the influence of phosphorylation on the structure and function of EPRS. We suggest that application of these approaches will help to identify new functional phosphorylation event(s) in other AARSs and elucidate their possible roles in noncanonical activities.

CRMPs Function in Neurons and Glial Cells: Potential Therapeutic Targets for Neurodegenerative Diseases and CNS Injury

Neurodegeneration in the adult mammalian central nervous system (CNS) is fundamentally accelerated by its intrinsic neuronal mechanisms, including its poor regenerative capacity and potent extrinsic inhibitory factors. Thus, the treatment of neurodegenerative diseases faces many obstacles. The degenerative processes, consisting of axonal/dendritic structural disruption, abnormal axonal transport, release of extracellular factors, and inflammation, are often controlled by the cytoskeleton. From this perspective, regulators of the cytoskeleton could potentially be a therapeutic target for neurodegenerative diseases and CNS injury. Collapsin response mediator proteins (CRMPs) are known to regulate the assembly of cytoskeletal proteins in neurons, as well as control axonal growth and neural circuit formation. Recent studies have provided some novel insights into the roles of CRMPs in several inhibitory signaling pathways of neurodegeneration, in addition to its functions in neurological disorders and CNS repair. Here, we summarize the roles of CRMPs in axon regeneration and its emerging functions in non-neuronal cells, especially in inflammatory responses. We also discuss the direct and indirect targeting of CRMPs as a novel therapeutic strategy for neurological diseases.