Suppression of ischemia in arterial occlusive disease by JNK-promoted native collateral artery development

Molecular insights into the role of mixed lineage kinase 3 in cancer hallmarks

Mixed-lineage kinase 3 (MLK3) is a serine/threonine kinase of the MAPK Kinase kinase (MAP3K) family that plays critical roles in various biological processes, including cancer. Upon activation, MLK3 differentially activates downstream MAPKs, such as JNK, p38, and ERK. In addition, it regulates various non-canonical signaling pathways, such as β-catenin, AMPK, Pin1, and PAK1, to regulate cell proliferation, apoptosis, invasion, and metastasis. Recent studies have also uncovered other potentially diverse roles of MLK3 in malignancy, which include metabolic reprogramming, cancer-associated inflammation, and evasion of cancer-related immune surveillance. The role of MLK3 in cancer is complex and cancer-specific, and an understanding of its function at the molecular level aligned specifically with the cancer hallmarks will have profound therapeutic implications for diagnosing and treating MLK3-dependent cancers. This review summarizes the current knowledge about the effect of MLK3 on the hallmarks of cancer, providing insights into its potential as a promising anticancer drug target.

Disruption of DLL4/NOTCH1 Causes Dysregulated PPARγ/AKT Signaling in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a progressive cardiopulmonary disease characterized by vascular remodeling of small pulmonary arteries. Endothelial dysfunction in advanced PAH is associated with proliferation, apoptosis resistance, and endothelial to mesenchymal transition (EndoMT) due to aberrant signaling. DLL4, a cell membrane associated NOTCH ligand, activates NOTCH1 signaling and plays a pivotal role maintaining vascular integrity. Inhibition of DLL4 has been associated with the development of pulmonary hypertension, but the mechanism is incompletely understood. Here we report that BMPR2 silencing in PAECs activated AKT and decreased DLL4 expression. DLL4 loss was also seen in lungs of patients with IPAH and HPAH. Over-expression of DLL4 in PAECs induced BMPR2 promoter activity and exogenous DLL4 increased BMPR2 mRNA through NOTCH1 activation. Furthermore, DLL4/NOTCH1 signaling blocked AKT activation, decreased proliferation and reversed EndoMT in BMPR2-silenced PAECs and ECs from IPAH patients. PPARγ, suppressed by BMPR2 loss, was induced and activated by DLL4/NOTCH1 signaling in both BMPR2-silenced and IPAH PAECs, reversing aberrant phenotypic changes, in part through AKT inhibition. Finally, leniolisib, a well-tolerated oral PI3Kδ/AKT inhibitor, decreased cell proliferation, induced apoptosis and reversed markers of EndoMT in BMPR2-silenced PAECs. Restoring DLL4/NOTCH1/PPARγ signaling and/or suppressing AKT activation may be beneficial in preventing or reversing the pathologic vascular remodeling of PAH.

Dysregulated Genes, MicroRNAs, Biological Pathways, and Gastrocnemius Muscle Fiber Types Associated With Progression of Peripheral Artery Disease: A Preliminary Analysis

Background Peripheral artery disease (PAD) is associated with gastrocnemius muscle abnormalities. However, the biological pathways associated with gastrocnemius muscle dysfunction and their associations with progression of PAD are largely unknown. This study characterized differential gene and microRNA (miRNA) expression in gastrocnemius biopsies from people without PAD compared with those with PAD. Participants with PAD included those with and without PAD progression. Methods and Results mRNA and miRNA sequencing were performed to identify differentially expressed genes, differentially expressed miRNAs, mRNA-miRNA interactions, and associated biological pathways for 3 sets of comparisons: (1) PAD progression (n=7) versus non-PAD (n=7); (2) PAD no progression (n=6) versus non-PAD; and (3) PAD progression versus PAD no progression. Immunohistochemistry was performed to determine gastrocnemius muscle fiber types and muscle fiber size. Differentially expressed genes and differentially expressed miRNAs were more abundant in the comparison of PAD progression versus non-PAD compared with PAD with versus without progression. Among the top significant cellular pathways in subjects with PAD progression were muscle contraction or development, transforming growth factor-beta, growth/differentiation factor, and activin signaling, inflammation, cellular senescence, and notch signaling. Subjects with PAD progression had increased frequency of smaller Type 2a gastrocnemius muscle fibers in exploratory analyses. Conclusions Humans with PAD progression exhibited greater differences in the number of gene and miRNA expression, biological pathways, and Type 2a muscle fiber size compared with those without PAD. Fewer differences were observed between people with PAD without progression and control patients without PAD. Further study is needed to confirm whether the identified transcripts may serve as potential biomarkers for diagnosis and progression of PAD.

p38 MAPK priming boosts VSMC proliferation and arteriogenesis by promoting PGC1α-dependent mitochondrial dynamics

Vascular smooth muscle cell (VSMC) proliferation is essential for arteriogenesis to restore blood flow after artery occlusion, but the mechanisms underlying this response remain unclear. Based on our previous findings showing increased VSMC proliferation in the neonatal aorta of mice lacking the protease MT4-MMP, we aimed at discovering new players in this process. We demonstrate that MT4-MMP absence boosted VSMC proliferation in vitro in response to PDGF-BB in a cell-autonomous manner through enhanced p38 MAPK activity. Increased phospho-p38 in basal MT4-MMP-null VSMCs augmented the rate of mitochondrial degradation by promoting mitochondrial morphological changes through the co-activator PGC1α as demonstrated in PGC1α^−/− VSMCs. We tested the in vivo implications of this pathway in a novel conditional mouse line for selective MT4-MMP deletion in VSMCs and in mice pre-treated with the p38 MAPK activator anisomycin. Priming of p38 MAPK activity in vivo by the absence of the protease MT4-MMP or by anisomycin treatment led to enhanced arteriogenesis and improved flow recovery after femoral artery occlusion. These findings may open new therapeutic opportunities for peripheral vascular diseases.

MLK3 mediates impact of PKG1α on cardiac function and controls blood pressure through separate mechanisms

cGMP-dependent protein kinase 1α (PKG1α) promotes left ventricle (LV) compensation after pressure overload. PKG1-activating drugs improve heart failure (HF) outcomes but are limited by vasodilation-induced hypotension. Signaling molecules that mediate PKG1α cardiac therapeutic effects but do not promote PKG1α-induced hypotension could therefore represent improved therapeutic targets. We investigated roles of mixed lineage kinase 3 (MLK3) in mediating PKG1α effects on LV function after pressure overload and in regulating BP. In a transaortic constriction HF model, PKG activation with sildenafil preserved LV function in MLK3+/+ but not MLK3-/- littermates. MLK3 coimmunoprecipitated with PKG1α. MLK3-PKG1α cointeraction decreased in failing LVs. PKG1α phosphorylated MLK3 on Thr277/Ser281 sites required for kinase activation. MLK3-/- mice displayed hypertension and increased arterial stiffness, though PKG stimulation with sildenafil or the soluble guanylate cyclase (sGC) stimulator BAY41-2272 still reduced BP in MLK3-/- mice. MLK3 kinase inhibition with URMC-099 did not affect BP but induced LV dysfunction in mice. These data reveal MLK3 as a PKG1α substrate mediating PKG1α preservation of LV function but not acute PKG1α BP effects. Mechanistically, MLK3 kinase-dependent effects preserved LV function, whereas MLK3 kinase-independent signaling regulated BP. These findings suggest augmenting MLK3 kinase activity could preserve LV function in HF but avoid hypotension from PKG1α activation.

A novel model of chronic limb ischemia to therapeutically evaluate the angiogenic effects of drug candidates

Critical limb ischemia (CLI) is a severe state of peripheral artery disease with high unmet clinical needs. Further, there are no effective treatment options for patients with CLI. Based on preclinical study results, predicting the clinical efficacy of CLI treatments is typically difficult because conventional hindlimb ischemia (HLI) rodent models display spontaneous recovery from ischemia, which is not observed in patients with CLI. Therefore, we aimed to develop a novel chronic and severe HLI model to properly evaluate the therapeutic effects of drug candidates for CLI. Severe HLI mice (Type-N) were generated by increasing the excised area of blood vessels in a hindlimb of NOG mice. Immunohistochemistry and gene expression analysis at 9 wk after the Type-N operation revealed that the ischemic limb was in a steady state with impaired angiogenesis, like that observed in patients with CLI. We did selection of chronic Type-N mice based on the number of necrotic nails and blood flow rate at 2 wk after surgery because some Type-N mice showed mild symptoms. Therapeutic treatment with cilostazol, which is used for intermittent claudication, did not restore blood flow in chronic Type-N mice. In contrast, therapeutic transplantation of pericytes and vascular endothelial cells, which can form new blood vessels in vivo, significantly improved blood flow in a subset of Type-N mice. These findings suggest that this novel chronic and severe HLI model may be a valuable standard animal model for therapeutic evaluation of the angiogenic effects of CLI drug candidates.NEW & NOTEWORTHY We developed a chronic and severe hindlimb ischemia (HLI) mouse model for preclinical research on critical limb ischemia (CLI). This model partially reflects human CLI pathology in that it does not show spontaneous restoration of blood flow or expression of angiogenic genes in the ischemic limb. This novel model may be valuable for therapeutic evaluation of the angiogenic effects of CLI drug candidates.

Diminished Expression of P-glycoprotein Using Focused Ultrasound Is Associated With JNK-Dependent Signaling Pathway in Cerebral Blood Vessels

MRI-guided focused ultrasound (MRgFUS) combined with microbubbles (MBs) is a promising technology that can facilitate drug delivery through a temporarily disrupted blood-brain barrier (BBB) and induce the down-regulation of P-glycoprotein (P-gp) expression on the blood vessels. Despite the increasing evidence regarding the down-regulation of P-gp expression after MRgFUS BBB disruption (BBBD), its underlying molecular events remain unclear. The aim of this study was to evaluate the underlying mechanism of FUS BBBD-mediated P-gp down-regulation. While our results showed down-regulation of P-gp at 24 h post-BBBD in transcriptional and translational levels, restoration to the normal expression appeared at different time points for transcriptional (72 h) and translational (120 h) levels. In addition, the signaling molecule, JNK, was significantly activated in the cerebral blood vessels at 24 h post-BBBD. Although P-gp levels were significantly decreased, the expression levels of proteins involved in the integrity of blood vessels, such as Glut1, ZO-1 and occludin, were not decreased at 24 h post-BBBD. Our study suggests that the JNK signaling pathway is involved in the regulation of FUS-induced P-gp expression, without affecting vessel integrity, and a detailed regulatory mechanism can provide the basis for clinical application of FUS to the treatment of neurological disease.

Neural JNK3 regulates blood flow recovery after hindlimb ischemia in mice via an Egr1/Creb1 axis

Diseases related to impaired blood flow such as peripheral artery disease (PAD) impact nearly 10 million people in the United States alone, yet patients with clinical manifestations of PAD (e.g., claudication and limb ischemia) have limited treatment options. In ischemic tissues, stress kinases such as c-Jun N-terminal kinases (JNKs), are activated. Here, we show that inhibition of the JNK3 (Mapk10) in the neural compartment strikingly potentiates blood flow recovery from mouse hindlimb ischemia. JNK3 deficiency leads to upregulation of growth factors such as Vegfa, Pdgfb, Pgf, Hbegf and Tgfb3 in ischemic muscle by activation of the transcription factors Egr1/Creb1. JNK3 acts through Forkhead box O3 (Foxo3a) to suppress the activity of Egr1/Creb1 transcription regulators in vitro. In JNK3-deficient cells, Foxo3a is suppressed which leads to Egr1/Creb1 activation and upregulation of downstream growth factors. Collectively, these data suggest that the JNK3-Foxo3a-Egr1/Creb1 axis coordinates the vascular remodeling response in peripheral ischemia.

Stress kinases are activated in peripheral ischemic tissues in the presence of vascular diseases. Here the authors show that inhibition of the neural JNK3 kinase improves recovery from hind limb ischemia in animals through activation of the transcription factors Egr1/Creb1 and upregulation of growth factors.

MLK3 silence induces cervical cancer cell apoptosis via the Notch-1/autophagy network

Mixed-lineage kinase 3 (MLK3), the mitogen-activated protein kinase kinase kinase (MAP3K), has been recognized as a player in tumorigenesis and oncogenic signalling, yet its detailed functions and signalling in cervical cancer have not been fully elucidated. Here, we identify that cervical cancer cells display higher mRNA and protein levels of MLK3 than normal cervical epithelial squamous cells. In HeLa and SiHa cell, MLK3 knockdown using siRNA remarkably suppressed cell survival and promoted cell apoptosis, with increased expression of the apoptosis-related protein Bax and reduced Bcl-2. Moreover, MLK3 knockdown promoted cell autophagy, demonstrated by increased ratio of autophagy-related proteins LC3II/LC3I and decreased p62 expression in MLK3 depletion cells. Furthermore, MLK3 knockdown remarkably abolished Notch-1 expression in cervical cancer cells. By co-treating Hela cells with MLK3 specific siRNA and pcDNA3.1-Notch-1 overexpression plasmid or autophagy inhibitor 3-MA, we found that MLK3 played its role in cervical cancer cells via the Notch-1/autophagy network. Our results demonstrate the importance of MLK3 in cervical cancer progression via modulating the Notch-1/autophagy network, and suggest that MLK3 is a promising therapeutic target for cervical cancer.

JNK and cardiometabolic dysfunction

Cardiometabolic syndrome (CMS) describes the cluster of metabolic and cardiovascular diseases that are generally characterized by impaired glucose tolerance, intra-abdominal adiposity, dyslipidemia, and hypertension. CMS currently affects more than 25% of the world’s population and the rates of diseases are rapidly rising. These CMS conditions represent critical risk factors for cardiovascular diseases including atherosclerosis, heart failure, myocardial infarction, and peripheral artery disease (PAD). Therefore, it is imperative to elucidate the underlying signaling involved in disease onset and progression. The c-Jun N-terminal Kinases (JNKs) are a family of stress signaling kinases that have been recently indicated in CMS. The purpose of this review is to examine the in vivo implications of JNK as a potential therapeutic target for CMS. As the constellation of diseases associated with CMS are complex and involve multiple tissues and environmental triggers, carefully examining what is known about the JNK pathway will be important for specificity in treatment strategies.

Sema3E/PlexinD1 signaling inhibits postischemic angiogenesis by regulating endothelial DLL4 and filopodia formation in a rat model of ischemic stroke

Angiogenesis is a crucial defense response to hypoxia that regulates the process of raising the promise of long-term neurologic recovery during the management of stroke. A high expression of antiangiogenic factors leads to the loss of neovascularization capacity in pathologic conditions. We have previously documented an impairment of the cerebral vessel perfusion and neovascularization in the cortex neighboring the stroke-induced lesion, which was accompanied by an activation of semaphorin 3E (Sema3E)/PlexinD1 after ischemic stroke. In this study, we employed micro-optical sectioning tomography to fully investigate the details of the vascular pattern, including the capillaries. We found that after transient middle cerebral artery occlusion, inhibiting PlexinD1 signaling led to an organized recovery of the vascular network in the ischemic area. We then further explored the possible mechanisms. In vivo, Sema3E substantially decreased dynamic delta-like 4 (DLL4) expression. In cultured brain microvascular endothelial cells, Sema3E down-regulated DLL4 expression via inhibiting Ras-related C3 botulinum toxin substrate 1-induced JNK phosphorylation. At the microcosmic level, Sema3E/PlexinD1 signaling promoted F-actin disassembly and focal adhesion reduction by activating the small guanosine triphosphatase Ras homolog family member J by releasing RhoGEF Tuba from direct binding to PlexinD1, thus mediating endothelial cell motility and filopodia retraction. Our study reveals that Sema3E/PlexinD1 signaling, which suppressed endothelial DLL4 expression, cell motility, and filopodia formation, is expected to be a novel druggable target for angiogenesis during poststroke progression.-Zhou, Y.-F., Chen, A.-Q., Wu, J.-H., Mao, L., Xia, Y.-P., Jin, H.-J., He, Q.-W., Miao, Q. R., Yue, Z.-Y., Liu, X.-L., Huang, M., Li, Y.-N., Hu, B. Sema3E/PlexinD1 signaling inhibits postischemic angiogenesis by regulating endothelial DLL4 and filopodia formation in a rat model of ischemic stroke.

Mixed lineage kinase-3 prevents cardiac dysfunction and structural remodeling with pressure overload

Myocardial hypertrophy is an independent risk factor for heart failure (HF), yet the mechanisms underlying pathological cardiomyocyte growth are incompletely understood. The c-Jun NH2-terminal kinase (JNK) signaling cascade modulates cardiac hypertrophic remodeling, but the upstream factors regulating myocardial JNK activity remain unclear. In this study, we sought to identify JNK-activating molecules as novel regulators of cardiac remodeling in HF. We investigated mixed lineage kinase-3 (MLK3), a master regulator of upstream JNK-activating kinases, whose role in the remodeling process had not previously been studied. We observed increased MLK3 protein expression in myocardium from patients with nonischemic and hypertrophic cardiomyopathy and in hearts of mice subjected to transverse aortic constriction (TAC). Mice with genetic deletion of MLK3 (MLK3-/-) exhibited baseline cardiac hypertrophy with preserved cardiac function. MLK3-/- mice subjected to chronic left ventricular (LV) pressure overload (TAC, 4 wk) developed worsened cardiac dysfunction and increased LV chamber size compared with MLK3+/+ littermates ( n = 8). LV mass, pathological markers of hypertrophy ( Nppa, Nppb), and cardiomyocyte size were elevated in MLK3-/- TAC hearts. Phosphorylation of JNK, but not other MAPK pathways, was selectively impaired in MLK3-/- TAC hearts. In adult rat cardiomyocytes, pharmacological MLK3 kinase inhibition using URMC-099 blocked JNK phosphorylation induced by neurohormonal agents and oxidants. Sustained URMC-099 exposure induced cardiomyocyte hypertrophy. These data demonstrate that MLK3 prevents adverse cardiac remodeling in the setting of pressure overload. Mechanistically, MLK3 activates JNK, which in turn opposes cardiomyocyte hypertrophy. These results support modulation of MLK3 as a potential therapeutic approach in HF. NEW & NOTEWORTHY Here, we identified a role for mixed lineage kinase-3 (MLK3) as a novel antihypertrophic and antiremodeling molecule in response to cardiac pressure overload. MLK3 regulates phosphorylation of the stress-responsive JNK kinase in response to pressure overload and in cultured cardiomyocytes stimulated with hypertrophic agonists and oxidants. This study reveals MLK3-JNK signaling as a novel cardioprotective signaling axis in the setting of pressure overload.

JNK at the crossroad of obesity, insulin resistance, and cell stress response

BACKGROUND

The cJun-N-terminal-kinase (JNK) plays a central role in the cell stress response, with outcomes ranging from cell death to cell proliferation and survival, depending on the specific context. JNK is also one of the most investigated signal transducers in obesity and insulin resistance, and studies have identified new molecular mechanisms linking obesity and insulin resistance. Emerging evidence indicates that whereas JNK1 and JNK2 isoforms promote the development of obesity and insulin resistance, JNK3 activity protects from excessive adiposity. Furthermore, current evidence indicates that JNK activity within specific cell types may, in specific stages of disease progression, promote cell tolerance to the stress associated with obesity and type-2 diabetes.

SCOPE OF REVIEW

This review provides an overview of the current literature on the role of JNK in the progression from obesity to insulin resistance, NAFLD, type-2 diabetes, and diabetes complications.

MAJOR CONCLUSION

Whereas current evidence indicates that JNK1/2 inhibition may improve insulin sensitivity in obesity, the role of JNK in the progression from insulin resistance to diabetes, and its complications is largely unresolved. A better understanding of the role of JNK in the stress response to obesity and type-2 diabetes, and the development of isoform-specific inhibitors with specific tissue distribution will be necessary to exploit JNK as possible drug target for the treatment of type-2 diabetes.