Correlation between the expression of miRNA-142-3p,mixed lineage kinase 3 and interleukin-1beta in nucleus pulposus and the degree of lumbar intervertebral disc degeneration / 中国组织工程研究

BACKGROUND:MicroRNA(miRNA)levels are closely related to cell apoptosis and proliferation,extracellular matrix metabolism and inflammatory response in intervertebral disc cells.However,the specific role of miR-142-3p in lumbar intervertebral disc degeneration remains unclear. OBJECTIVE:To investigate the correlation between the expression of miRNA-142-3p,mixed lineage kinase 3 and interleukin-1β in nucleus pulposus tissue and degree of human lumbar intervertebral disc degeneration. METHODS:A total of 82 patients with lumbar intervertebral disc degenerative diseases in Suzhou Ninth People's Hospital from January 2020 to March 2022 were collected as the study subjects,all of whom underwent MRI examination before operation.According to the Videman classification,the patients were divided into mild degeneration group(n=36),moderate degeneration group(n=26)and severe degeneration group(n=20).Eighty-two specimens of the nucleus pulposus were obtained.The mRNA expression of miRNA-142-3p as well as the mRNA and protein expression of mixed lineage kinase 3,interleukin-1β,type I collagen,type II collagen in nucleus pulposus tissue were detected by qPCR and western blot assay.The correlation between the degree of human lumbar intervertebral disc degeneration and the expression levels of miRNA-142-3p,mixed lineage kinase 3,and interleukin-1β was also assessed using the Spearman correlation coefficient method.Thirty adult Sprague-Dawley rats were divided into sham-operated group(executed after puncturing skin and muscle only),mild degeneration group(executed 1 week after puncturing Co7/8 segments)and severe degeneration group(executed 2 weeks after puncturing Co7/8 segments),with 10 rats in each group.After that,we detected the protein expression of mixed lineage kinase 3 and interleukin-1β as well as the gene expression of miRNA-142-3p,mixed lineage kinase 3 and interleukin-1β in the nucleus pulposus tissue. RESULTS AND CONCLUSION:In human nucleus pulposus tissue,the miRNA-142-3p expression ranked from high to low as follows:mild degeneration group>moderate degeneration group>severe degeneration group(P<0.05);the gene and protein expression of mixed lineage kinase 3 and interleukin-1β from low to high was as follows:mild degeneration group<moderate degeneration group<severe degeneration group(P<0.05);the gene and protein expression of type I collagen from low to high was as follows:mild degeneration group<moderate degeneration group<severe degeneration group(P<0.05),and the gene and protein expression of type I collagen from high to low was as follows:mild degeneration group>moderate degeneration group>severe degeneration group(P<0.05).Spearman correlation analysis showed that the degree of disc degeneration was negatively correlated with miRNA-142-3p expression(P<0.05)and positively correlated with mixed lineage kinase 3 and interleukin-1β expression(P<0.05).In rat nucleus pulposus tissue,compared with the sham-operated group,the expression of mixed lineage kinase 3 and interleukin-1β gene and protein was elevated in the mild degeneration group(P<0.05)while miRNA-142-3p expression was decreased(P<0.05);compared with the mild degeneration group,the expression of mixed lineage kinase 3 and interleukin-1β gene and protein was increased in the severe degeneration group(P<0.05)while miRNA-142-3p expression was decreased(P<0.05).To conclude,the degree of human lumbar intervertebral disc degeneration is negatively correlated with miRNA-142-3p expression and positively correlated with mixed lineage kinase 3 and interleukin-1β expression in nucleus pulposus tissue.

[Generation of Mlk3 KO mice by CRISPR/Cas9 and its effect on blood pressure].

To explore the effect of Mlk3 (mixed lineage kinase 3) deficiency on blood pressure, Mlk3 gene knockout (Mlk3KO) mice were generated. Activities of sgRNAs targeted Mlk3 gene were evaluated by T7 endonuclease I (T7E1) assay. CRISPR/Cas9 mRNA and sgRNA were obtained by in vitro transcription, microinjected into zygote, followed by transferring into a foster mother. Genotyping and DNA sequencing confirmed the deletion of Mlk3 gene. Real- time PCR (RT-PCR), Western blotting or immunofluorescence analysis showed that Mlk3KO mice had an undetectable expression of Mlk3 mRNA or Mlk3 protein. Mlk3KO mice exhibited an elevated systolic blood pressure compared with wild-type mice as measured by tail-cuff system. Immunohistochemistry and Western blotting analysis showed that the phosphorylation of MLC (myosin light chain) was significantly increased in aorta isolated from Mlk3KO mice. Together, Mlk3KO mice was successfully generated by CRISPR/Cas9 system. MLK3 functions in maintaining blood pressure homeostasis by regulating MLC phosphorylation. This study provides an animal model for exploring the mechanism by which Mlk3 protects against the development of hypertension and hypertensive cardiovascular remodeling.

Generation of Mlk3 KO mice by CRISPR/Cas9 and its effect on blood pressure / 生物工程学报

To explore the effect of Mlk3 (mixed lineage kinase 3) deficiency on blood pressure, Mlk3 gene knockout (Mlk3KO) mice were generated. Activities of sgRNAs targeted Mlk3 gene were evaluated by T7 endonuclease I (T7E1) assay. CRISPR/Cas9 mRNA and sgRNA were obtained by in vitro transcription, microinjected into zygote, followed by transferring into a foster mother. Genotyping and DNA sequencing confirmed the deletion of Mlk3 gene. Real- time PCR (RT-PCR), Western blotting or immunofluorescence analysis showed that Mlk3KO mice had an undetectable expression of Mlk3 mRNA or Mlk3 protein. Mlk3KO mice exhibited an elevated systolic blood pressure compared with wild-type mice as measured by tail-cuff system. Immunohistochemistry and Western blotting analysis showed that the phosphorylation of MLC (myosin light chain) was significantly increased in aorta isolated from Mlk3KO mice. Together, Mlk3KO mice was successfully generated by CRISPR/Cas9 system. MLK3 functions in maintaining blood pressure homeostasis by regulating MLC phosphorylation. This study provides an animal model for exploring the mechanism by which Mlk3 protects against the development of hypertension and hypertensive cardiovascular remodeling.

Phosphorylation of mixed lineage kinase MLK3 by cyclin-dependent kinases CDK1 and CDK2 controls ovarian cancer cell division.

Mixed lineage kinase 3 (MLK3) is a serine/threonine mitogen-activated protein kinase kinase kinase that promotes the activation of multiple mitogen-activated protein kinase pathways and is required for invasion and proliferation of ovarian cancer cells. Inhibition of MLK activity causes G2/M arrest in HeLa cells; however, the regulation of MLK3 during ovarian cancer cell cycle progression is not known. Here, we found that MLK3 is phosphorylated in mitosis and that inhibition of cyclin-dependent kinase 1 (CDK1) prevented MLK3 phosphorylation. In addition, we observed that c-Jun N-terminal kinase, a downstream target of MLK3 and a direct target of MKK4 (SEK1), was activated in G2 phase when CDK2 activity is increased and then inactivated at the beginning of mitosis concurrent with the increase in CDK1 and MLK3 phosphorylation. Using in vitro kinase assays and phosphomutants, we determined that CDK1 phosphorylates MLK3 on Ser548 and decreases MLK3 activity during mitosis, whereas CDK2 phosphorylates MLK3 on Ser770 and increases MLK3 activity during G1/S and G2 phases. We also found that MLK3 inhibition causes a reduction in cell proliferation and a cell cycle arrest in ovarian cancer cells, suggesting that MLK3 is required for ovarian cancer cell cycle progression. Taken together, our results suggest that phosphorylation of MLK3 by CDK1 and CDK2 is important for the regulation of MLK3 and c-Jun N-terminal kinase activities during G1/S, G2, and M phases in ovarian cancer cell division.

Silence of MLK3 alleviates lipopolysaccharide-induced lung epithelial cell injury via inhibiting p53-mediated ferroptosis.

Acute lung injury (ALI) is characterized with a high rate of morbidity and mortality. The injury and apoptosis of lung epithelial cells play crucial roles in the progression of ALI. Mixed lineage kinase 3 (MLK3) has been reported to be involved in the regulation of cellular biological functions, such as cell proliferation, apoptosis and ferroptosis. However, the effect of MLK3 exerted on ALI has not been reported. Here, LPS-stimulated MLE12 pulmonary epithelial cells were used as an in vitro model for ALI. In this research, LPS elevated the expression of MLK3 in MLE12 cells. The silence of MLK3 alleviated LPS-induced cell injury. Notably, LPS promoted ferroptosis through enhancing GSH depletion and the productions of MDA and iron, which was attenuated by MLK3 knockdown. Moreover, the silence of MLK3 inhibited p53 expression in LPS-induced cells along with a decrease in the expressions of p21 and Bax, while overexpressing p53 reversed these effects of MLK3 silence. Meanwhile, p53 overexpression reversed the positive effects of MLK3 knockdown on LPS-induced cell ferroptosis and injury. Together, our results confirmed that the silence of MLK3 alleviated LPS-induced lung epithelial cell injury by inhibiting p53-mediated ferroptosis.

Hyperoside protects cardiomyocytes against hypoxia­induced injury via upregulation of microRNA­138.

Following hypoxia, cardiomyocytes are susceptible to damage, against which microRNA (miR)­138 may act protectively. Hyperoside (Hyp) is a Chinese herbal medicine with multiple biological functions that serve an important role in cardiovascular disease. The aim of the present study was to investigate the role of Hyp in hypoxic cardiomyocytes and its effect on miR­138. A hypoxia model was established in both H9C2 cells and C57BL/6 mice, which were stimulated by Hyp. The expression levels of miR­138 were increased in the hypoxic myocardium in the presence of Hyp at concentrations of >50 µmol/l in vivo and >50 mg/kg in vitro. Using Cell Counting Kit­8 and 5­ethynyl­2'­deoxyuridine assays, it was observed that Hyp improved hypoxia­induced impairment of cell proliferation. Cell apoptosis was evaluated by flow cytometry and a TUNEL assay. The number of apoptotic cells in the Hyp group was lower than that in the control group. As markers of myocardial injury, the levels of lactate dehydrogenase, creatine kinase­myocardial band isoenzyme and malondialdehyde were decreased in the Hyp group compared with the control group, whereas the levels of superoxide dismutase were increased. A marked decrease in the levels of cleaved caspase­3 and cleaved poly(ADP) ribose polymerase and a marked increase in expression levels of Bcl­2 were observed in the presence of Hyp. However, miR­138 inhibition by antagomir attenuated the protective effects of Hyp. Furthermore, Hyp treatment was associated with marked downregulation of mixed lineage kinase 3 and lipocalin­2, but not pyruvate dehydrogenase kinase 1, in hypoxic H9C2 cells. These findings demonstrated that Hyp may be beneficial for myocardial cell survival and may alleviate hypoxic injury via upregulation of miR­138, thereby representing a promising potential strategy for clinical cardioprotection.

The regulatory function of mixed lineage kinase 3 in tumor and host immunity.

Protein kinases are the second most sought-after G-protein coupled receptors as drug targets because of their overexpression, mutations, and dysregulated catalytic activities in various pathological conditions. Till 2019, 48 protein kinase inhibitors have received FDA approval for the treatment of multiple illnesses, of which the majority of them are indicated for different malignancies. One of the attractive sub-group of protein kinases that has attracted attention for drug development is the family members of MAPKs that are recognized to play significant roles in different cancers. Several inhibitors have been developed against various MAPK members; however, none of them as monotherapy has shown sustainable efficacy. One of the MAPK members, called Mixed Lineage Kinase 3 (MLK3), has attracted considerable attention due to its role in inflammation and neurodegenerative diseases; however, its role in cancer is an emerging area that needs more investigation. Recent advances have shown that MLK3 plays a role in cancer cell survival, migration, drug resistance, cell death, and tumor immunity. This review describes how MLK3 regulates different MAPK pathways, cancer cell growth and survival, apoptosis, and host's immunity. We also discuss how MLK3 inhibitors can potentially be used along with immunotherapy for different malignancies.

MLK3 Is Associated With Poor Prognosis in Patients With Glioblastomas and Actin Cytoskeleton Remodeling in Glioblastoma Cells.

Mixed lineage kinase 3 (MLK3) has been implicated in human melanoma and breast cancers. However, the clinical significance of MLK3 in human gliomas and the underlying cellular and molecular mechanisms remain unclear. We found that MLK3 proteins were highly expressed in high-grade human glioma specimens and especially prevalent in primary and recurrent glioblastoma multiforme (GBM). High levels of MLK3 mRNA were correlated with poor prognosis in patients with isocitrate dehydrogenase (IDH)-wild-type (wt) gliomas. Furthermore, genetic ablation of MLK3 significantly suppressed the migration and invasion abilities of GBM cells and disrupted actin cytoskeleton organization. Importantly, MLK3 directly bound to epidermal growth factor receptor kinase substrate 8 (EPS8) and regulated the cellular location of EPS8, which is essential for actin cytoskeleton rearrangement. Overall, these findings provide evidence that MLK3 upregulation predicts progression and poor prognosis in human IDH-wt gliomas and suggest that MLK3 promotes the migration and invasion of GBM cells by remodeling the actin cytoskeleton via MLK3-EPS8 signaling.

The broad spectrum mixed-lineage kinase 3 inhibitor URMC-099 prevents acute microgliosis and cognitive decline in a mouse model of perioperative neurocognitive disorders.

BACKGROUND: Patients with pre-existing neurodegenerative disease commonly experience fractures that require orthopedic surgery. Perioperative neurocognitive disorders (PND), including delirium and postoperative cognitive dysfunction, are serious complications that can result in increased 1-year mortality when superimposed on dementia. Importantly, there are no disease-modifying therapeutic options for PND. Our lab developed the "broad spectrum" mixed-lineage kinase 3 inhibitor URMC-099 to inhibit pathological innate immune responses that underlie neuroinflammation-associated cognitive dysfunction. Here, we test the hypothesis that URMC-099 can prevent surgery-induced neuroinflammation and cognitive impairment. METHODS: Orthopedic surgery was performed by fracturing the tibia of the left hindlimb with intramedullary fixation under general anesthesia and analgesia. In a pilot experiment, 9-month-old mice were treated five times with URMC-099 (10 mg/kg, i.p.), spaced 12 h apart, with three doses prior to surgery and two doses following surgery. In this experiment, microgliosis was evaluated using unbiased stereology and blood-brain barrier (BBB) permeability was assessed using immunoglobulin G (IgG) immunostaining. In follow-up experiments, 3-month-old mice were treated only three times with URMC-099 (10 mg/kg, i.p.), spaced 12 h apart, prior to orthopedic surgery. Two-photon scanning laser microscopy and CLARITY with light-sheet microscopy were used to define surgery-induced changes in microglial dynamics and morphology, respectively. Surgery-induced memory impairment was assessed using the "What-Where-When" and Memory Load Object Discrimination tasks. The acute peripheral immune response to surgery was assessed by cytokine/chemokine profiling and flow cytometry. Finally, long-term fracture healing was assessed in fracture callouses using micro-computerized tomography (microCT) and histomorphometry analyses. RESULTS: Orthopedic surgery induced BBB disruption and microglial activation, but had no effect on microglial process motility. Surgically treated mice exhibited impaired object place and identity discrimination in the "What-Where-When" and Memory Load Object Discrimination tasks. Both URMC-099 dosing paradigms prevented the neuroinflammatory sequelae that accompanied orthopedic surgery. URMC-099 prophylaxis had no effect on the mobilization of the peripheral innate immune response and fracture healing. CONCLUSIONS: These findings show that prophylactic URMC-099 treatment is sufficient to prevent surgery-induced microgliosis and cognitive impairment without affecting fracture healing. Together, these findings provide compelling evidence for the advancement of URMC-099 as a therapeutic option for PND.

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.

The second generation mixed lineage kinase-3 (MLK3) inhibitor CLFB-1134 protects against neurotoxin-induced nigral dopaminergic neuron loss.

Dopaminergic neurons express mixed lineage kinases which regulate the expression of cell death genes. In Parkinson's disease, cell death via apoptosis is prevalent, and previous work testing mixed lineage kinase inhibitors in animal models suggested the inhibitors had some neuroprotective potential. CLFB-1134 is a new, brain-penetrant inhibitor specific for MLK3, tested here in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of dopaminergic depletion and nigral neuron death in mice. After ensuring that treatment with CLFB-1134 did not alter conversion of MPTP to MPP+, we demonstrated CLFB-1134's inhibition of MLK3 and neuroprotective efficacy. Specifically we evaluated the integrity of the nigrostriatal dopamine system following MPTP by assessing protein expression, high performance liquid chromatography, and immunohistology with stereology. We found that CLFB-1134 achieves protection of striatal dopaminergic terminals and nigral cell bodies when dosed simultaneously or following MPTP treatment. By preventing phosphorylation of JNK and other downstream targets of MLK3, CLFB-1134 protects against the neurotoxin MPTP. Inhibition of MLK3 may be a valid target for future work investigating treatment of Parkinson's disease.

miRNA-138 regulates MLK3/JNK/MAPK pathway to protect BV-2 cells from H2O2-induced apoptosis.

BACKGROUND: miR-138 is one of the down-regulated miRNAs during acute spinal cord injury. Mixed lineage kinase 3 (MLK3), a key factor of jun N-terminal kinase (JNK)/mitogen-activated protein kinase (MAPK) pathway, is the target of miR-138. The aim of this study was to investigate the role of miR-138 in H2O2-treated BV-2 cells. METHODS: Murine microglia BV-2 cells were treated with H2O2 and tested for cell viability and miR-138 expression. The cells were then transfected with miR-138 agomir or miR-138 antagomir, and treated with 200 µM H2O2 for 24 h. The cellular apoptosis was detected by Aennexin V/PI staining. Expression of miR-138, MLK3, and other factors of JNK/MAPK pathway was detected. RESULTS: After treatment of various concentrations of H2O2, the cell viabilities were reduced, and miR-138 expression was down-regulated. Compared to the control cells, over-expressing miR-138 in BV-2 cells reduced apoptosis rate from 24.2 % to 11.9 %. Western blot further showed that JNK, p-JNK, c-jun, p-c-jun, p38 MAPK, and p-p38 MAPK were down-regulated. Expression of pro-apoptosis factors iNOS and COX-2 were also down-regulated. Transfection of miR-138 antagomir produced the opposite effect of the transfection of miR-138 agomir. CONCLUSION: miR-138 was able to reduce H2O2-induced apoptosis in BV-2 cells. The protective effect was related to the down-regulation of MLK3 proteins and sequentially inhibiting JNK/MAPK signaling pathway (Fig. 3, Ref. 27). Text in PDF www.elis.sk.

Osmotic and heat stress-dependent regulation of MLK4ß and MLK3 by the CHIP E3 ligase in ovarian cancer cells.

Mixed Lineage Kinase 3 (MLK3), a member of the MLK subfamily of protein kinases, is a mitogen-activated protein (MAP) kinase kinase kinase (MAP3K) that activates MAPK signalling pathways and regulates cellular responses such as proliferation, invasion and apoptosis. MLK4ß, another member of the MLK subfamily, is less extensively studied, and the regulation of MLK4ß by stress stimuli is not known. In this study, the regulation of MLK4ß and MLK3 by osmotic stress, thermostress and heat shock protein 90 (Hsp90) inhibition was investigated in ovarian cancer cells. MLK3 and MLK4ß protein levels declined under conditions of prolonged osmotic stress, heat stress or exposure to the Hsp90 inhibitor geldanamycin (GA); and MLK3 protein declined faster than MLK4ß. Similar to MLK3, the reduction in MLK4ß protein in cells exposed to heat or osmotic stresses occurred via a mechanism that involves the E3 ligase, carboxy-terminus of Hsc70-interacting protein (CHIP). Both heat shock protein 70 (Hsp70) and CHIP overexpression led to polyubiquitination and a decrease in endogenous MLK4ß protein, and MLK4ß was ubiquitinated by CHIP in vitro. In untreated cells and cells exposed to osmotic and heat stresses for short time periods, small interfering RNA (siRNA) knockdown of MLK4ß elevated the levels of activated MLK3, c-Jun N-terminal kinase (JNK) and p38 MAPKs. Furthermore, MLK3 binds to MLK4ß, and this association is regulated by osmotic stress. These results suggest that in the early response to stressful stimuli, MLK4ß-MLK3 binding is important for regulating MLK3 activity and MAPK signalling, and after prolonged periods of stress exposure, MLK4ß and MLK3 proteins decline via CHIP-dependent degradation. These findings provide insight into how heat and osmotic stresses regulate MLK4ß and MLK3, and reveal an important function for MLK4ß in modulating MLK3 activity in stress responses.

Effects of DL-3-n-Butylphthalide on Proliferation and Apoptosis of 1-Methyl-4-Phenylpyridinium-induced SH-SY5Y Cells via Mixed Lineage Kinase 3 Signaling Pathway / 中国康复理论与实践

Objective To investigate the effects of DL-3-n-Butylphthalide(NBP)on proliferation and apoptosis of 1-methyl-4-phenyl-pyridinium (MPP +)-induced SH-SY5Y cells, and mechanisms via mixed lineage kinase 3 (MLK3) signaling pathway. Methods The SH-SY5Y cells were divided into control group,MPP+group,NBP group and URMC-099 group,that cultured normally,with 1 mmol/L MPP+for 24 hours,with 10μmol/L NBP for 3 hours and then with MPP+for 24 hours,and with 200 nmol/L MLK3 inhibitor URMC-099 for 3 hours and then with MPP+for 24 hours,respectively.The morphology of SH-SY5Y cells was observed under inverted phase contrast mi-croscope and the survival rate was measured with 3-(4,5-Cimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assays.The apoptosis was quantified under flow cytometry with Annexin V/PI fluorescence staining,and the nuclear morphology was observed with Hoechst 33342 staining.The expression of phosphorylated protein of MLK3(p-MLK3),c-Jun N-terminal kinase(p-JNK),extra cellular regulated protein ki-nases(p-ERK1/2)were detected with Western blotting.Results Compared with the control group,the survival rate reduced and apoptosis in-creased in MPP+group(P<0.05),with the increase of p-MLK3 and p-JNK and decrease of p-ERK1/2 d(P<0.05).Compared with MPP+group,the survival rate increased and apoptosis reduced in both NBP and URMC-099 groups(P<0.05),with the decrease of p-MLK3 and p-JNK and increase of p-ERK1/2(P<0.05).Conclusion NBP can decrease the apoptosis and promote the proliferation of SH-SY5Y cells in-duced by MPP+,which may be associated with inhibiting MLK3 signaling pathway,and regulating the downstream p-JNK and p-ERK1/2.

The mixed-lineage kinase 3 inhibitor URMC-099 facilitates microglial amyloid-ß degradation.

BACKGROUND: Amyloid-ß (Aß)-stimulated microglial inflammatory responses engage mitogen-activated protein kinase (MAPK) pathways in Alzheimer's disease (AD). Mixed-lineage kinases (MLKs) regulate upstream MAPK signaling that include p38 MAPK and c-Jun amino-terminal kinase (JNK). However, whether MLK-MAPK pathways affect Aß-mediated neuroinflammation is unknown. To this end, we investigated if URMC-099, a brain-penetrant small-molecule MLK type 3 inhibitor, can modulate Aß trafficking and processing required for generating AD-associated microglial inflammatory responses. METHODS: Aß1-42 (Aß42) and/or URMC-099-treated murine microglia were investigated for phosphorylated mitogen-activated protein kinase kinase (MKK)3, MKK4 (p-MKK3, p-MKK4), p38 (p-p38), and JNK (p-JNK). These pathways were studied in tandem with the expression of the pro-inflammatory cytokines interleukin (IL)-1ß, IL-6, and tumor necrosis factor (TNF)-α. Gene expression of the anti-inflammatory cytokines, IL-4 and IL-13, was evaluated by real-time quantitative polymerase chain reaction. Aß uptake and expression of scavenger receptors were measured. Protein trafficking was assessed by measures of endolysosomal markers using confocal microscopy. RESULTS: Aß42-mediated microglial activation pathways were shown by phosphorylation of MKK3, MKK4, p38, and JNK and by expression of IL-1ß, IL-6, and TNF-α. URMC-099 modulated microglial inflammatory responses with induction of IL-4 and IL-13. Phagocytosis of Aß42 was facilitated by URMC-099 with up-regulation of scavenger receptors. Co-localization of Aß and endolysosomal markers associated with enhanced Aß42 degradation was observed. CONCLUSIONS: URMC-099 reduced microglial inflammatory responses and facilitated phagolysosomal trafficking with associated Aß degradation. These data demonstrate a new immunomodulatory role for URMC-099 to inhibit MLK and to induce microglial anti-inflammatory responses. Thus, URMC-099 may be developed further as a novel disease-modifying AD therapy.

MLK3 Signaling in Cancer Invasion.

Mixed-lineage kinase 3 (MLK3) was first cloned in 1994; however, only in the past decade has MLK3 become recognized as a player in oncogenic signaling. MLK3 is a mitogen-activated protein kinase kinase kinase (MAP3K) that mediates signals from several cell surface receptors including receptor tyrosine kinases (RTKs), chemokine receptors, and cytokine receptors. Once activated, MLK3 transduces signals to multiple downstream pathways, primarily to c-Jun terminal kinase (JNK) MAPK, as well as to extracellular-signal-regulated kinase (ERK) MAPK, P38 MAPK, and NF-κB, resulting in both transcriptional and post-translational regulation of multiple effector proteins. In several types of cancer, MLK3 signaling is implicated in promoting cell proliferation, as well as driving cell migration, invasion and metastasis.

MLK3 is a novel target of dehydroglyasperin D for the reduction in UVB-induced COX-2 expression in vitro and in vivo.

Dehydroglyasperin D (DHGA-D), a compound present in licorice, has been found to exhibit anti-obesity, antioxidant and anti-aldose reductase effects. However, the direct molecular mechanism and molecular targets of DHGA-D during skin inflammation remain unknown. In the present study, we investigated the effect of DHGA-D on inflammation and its mechanism of action on UVB-induced skin inflammation in HaCaT human keratinocytes and SKH-1 hairless mice. DHGA-D treatment strongly suppressed UVB-induced COX-2 expression, PGE2 generation and AP-1 transactivity in HaCaT cells without affecting cell viability. DHGA-D also inhibited phosphorylation of the mitogen-activated protein kinase kinase (MKK) 3/6/p38, MAPK/Elk-1, MKK4/c-Jun N-terminal kinase (JNK) 1/2/c-Jun/mitogen, and stress-activated protein kinase (MSK), whereas phosphorylation of the mixed-lineage kinase (MLK) 3 remained unaffected. Kinase and co-precipitation assays with DHGA-D Sepharose 4B beads showed that DHGA-D significantly suppressed MLK3 activity through direct binding to MLK3. Knockdown of MLK3 suppressed COX-2 expression as well as phosphorylation of MKK4/p38 and MKK3/6/JNK1/2 in HaCaT cells. Furthermore, Western blot assay and immunohistochemistry results showed that DHGA-D pre-treatment significantly inhibits UVB-induced COX-2 expression in vivo. Taken together, these results indicate that DHGA-D may be a promising anti-inflammatory agent that mediates suppression of both COX-2 expression and the MLK3 signalling pathway through direct binding and inhibition of MLK3.

MLK3-MKK3/6-P38MAPK cascades following N-methyl-D-aspartate receptor activation contributes to amyloid-ß peptide-induced apoptosis in SH-SY5Y cells.

Amyloid-ß peptide (Aß) has been implicated in the development of Alzheimer's disease (AD), but the underlying molecular mechanisms remain unclear. The present study explores the proapoptosis signaling evoked by N-methyl-D-aspartate (NMDA) receptors in Aß neurotoxicity. Oligomeric Aß25-35 incubation resulted in significant apoptosis of neuronal SH-SY5Y cells. Preadministration of the potent NMDA receptor antagonist MK801 promoted neuronal survival. Both NVP-AAM077 and Ro25-6981, GluN2A- and GluN2B-subunit-selective NMDA receptor antagonists, respectively, showed effects similar to those of MK801, supporting a critical role of GluN2A- or GluN2B-containing NMDA receptors in Aß neurotoxicity. Exposure to oligomeric Aß25-35 increased the phosphorylation (activation) of mixed-lineage kinase 3 (MLK3), dual-specific mitogen-activated protein kinase kinase 3/6 (MKK3/6), and P38 mitogen-activated protein kinase (P38MAPK) in SH-SY5Y cells. Inhibition of P38MAPK activation by SB239063 had a neuroprotective effect. K252a attenuated the phosphorylation of MLK3, MKK3/6, and P38MAPK but also partially prevented SH-SY5Y cells apoptosis. MK801, NVP-AAM077, and Ro25-6981, abrogated the MLK3-MKK3/6-P38MAPK activation induced by oligomeric Aß25-35. These results suggest that the activation of GluN2A- or GluN2B-containing NMDA receptors is responsible for the activation of MLK3-MKK3/6-P38MAPK cascades, which contributes to Aß-mediated cell apoptosis.

MLK3 regulates fMLP-stimulated neutrophil motility.

INTRODUCTION: Mixed lineage kinase 3 (MLK3) is part of the intracellular regulatory system that connects extracellular cytokine or mitogen signals received through G-protein coupled receptors to changes in gene expression. MLK3 activation stimulates motility of epithelial cells and epithelial-derived tumor cells, but its role in mediating the migration of other cell types remains unknown. Since neutrophils play a crucial role in innate immunity and contribute to the pathogenesis of several diseases, we therefore examined whether MLK3 might regulate the motility of mouse neutrophils responding to a chemotactic stimulus, the model bacterial chemoattractant fMLP. METHODS: The expression of Mlk3 in mouse neutrophils was determined by immunocytochemistry and by RT-PCR. In vitro chemotaxis in a gradient of fMLP, fMLP-stimulated random motility, fMLP-stimulated F-actin formation were measured by direct microscopic observation using neutrophils pre-treated with a novel small molecule inhibitor of MLK3 (URMC099) or neutrophils obtained from Mlk3-/- mice. In vivo effects of MLK3 inhibition were measured by counting the fMLP-induced accumulation of neutrophils in the peritoneum following pre-treatment with URMC099 in wild-type C57Bl/6 or mutant Mlk3-/- mice. RESULTS: The expression of Mlk3 mRNA and protein was observed in neutrophils purified from wild-type C57Bl/6 mice but not in neutrophils from mutant Mlk3-/- mice. Chemotaxis by wild-type neutrophils induced by a gradient of fMLP was reduced by pre-treatment with URMC099. Neutrophils from C57Bl/6 mice pretreated with URMC099 and neutrophils from Mlk3-/- mice moved far less upon fMLP-stimulation and did not form F-actin as readily as untreated neutrophils from C57Bl/6 controls. In vivo recruitment of neutrophils into the peritoneum by fMLP was significantly reduced in wild-type mice treated with URMC099, as well as in untreated Mlk3-/- mice-thereby confirming the role of MLK3 in neutrophil migration. CONCLUSIONS: Mlk3 mRNA is expressed in murine neutrophils. Genetic or pharmacologic inhibition of MLK3 blocks fMLP-mediated motility of neutrophils both in vitro and in vivo, suggesting that MLK3 may be a therapeutic target in human diseases characterized by exuberant neutrophil migration.

Macrophage polarization and function with emphasis on the evolving roles of coordinated regulation of cellular signaling pathways.

Monocytes/macrophages are heterogeneous and versatile cells that could undergo their phenotypically/functionally dynamic switch in response to the microenvironment signals. Two major macrophage subpopulations with different functions which represent extreme of a continuum in a universe of activation states, including classically activated/inflammatory (M1) and alternatively activated/regenerative (M2) macrophages, have long been recognized. Emerging evidence through genetic or pharmacologic approaches has now been made in defining the actual fate in vivo and in vitro underlying M1 or M2-like polarized activation under physiological and pathological conditions. These cells are characterized by their expression of cell surface markers, secreted cytokines and chemokines, and transcription and epigenetic pathways. Here in this review, we shed new light on the contribution of several major signaling pathways and their modulators/targets involved in directing the macrophage plasticity and polarized function, assess the mechanisms of macrophage polarization by interacting endogenous cellular mechanisms and molecules associated with reciprocal skewing of macrophage polarization between the M1 and M2 states. The identification of mechanisms underlying functional polarization of macrophages into M1 or M2 cells might provide new insights into a basis for macrophage-centered diagnostic and therapeutic strategies for multiple diseases.