Regulation of TFEB nuclear localization by HSP90AA1 promotes autophagy and longevity.

TFEB (transcription factor EB) regulates multiple genes involved in the process of macroautophagy/autophagy and plays a critical role in lifespan determination. However, the detailed mechanisms that regulate TFEB activity are not fully clear. In this study, we identified a role for HSP90AA1 in modulating TFEB. HSP90AA1 was phosphorylated by CDK5 at Ser 595 under basal condition. This phosphorylation inhibited HSP90AA1, disrupted its binding to TFEB, and impeded TFEB's nuclear localization and subsequent autophagy induction. Pro-autophagy signaling attenuated CDK5 activity and enhanced TFEB function in an HSP90AA1-dependent manner. Inhibition of HSP90AA1 function or decrease in its expression significantly attenuated TFEB's nuclear localization and transcriptional function following autophagy induction. HSP90AA1-mediated regulation of a TFEB ortholog was involved in the extended lifespan of Caenorhabditis elegans in the absence of its food source bacteria. Collectively, these findings reveal that this regulatory process plays an important role in modulation of TFEB, autophagy, and longevity.Abbreviations : AL: autolysosome; AP: autophagosome; ATG: autophagy related; BafA1: bafilomycin A1; CDK5: cyclin-dependent kinase 5; CDK5R1: cyclin dependent kinase 5 regulatory subunit 1; CR: calorie restriction; FUDR: 5-fluorodeoxyuridine; HSP90AA1: heat shock protein 90 alpha family class A member 1; MAP1LC3: microtubule associated protein 1 light chain 3; NB: novobiocin sodium; SQSTM1: sequestosome 1; TFEB: transcription factor EB; WT: wild type.

Differentiation between glioma recurrence and treatment effects using amide proton transfer imaging: A mini-Bayesian bivariate meta-analysis.

Background: Amide proton transfer (APT) imaging as an emerging MRI approach has been used for distinguishing tumor recurrence (TR) and treatment effects (TEs) in glioma patients, but the initial results from recent studies are different. Aim: The aim of this study is to systematically review and quantify the diagnostic performance of APT in assessing treatment response in patients with post-treatment gliomas. Methods: A systematic search in PubMed, EMBASE, and the Web of Science was performed to retrieve related original studies. For the single and added value of APT imaging in distinguishing TR from TEs, we calculated pooled sensitivity and specificity by using Bayesian bivariate meta-analyses. Results: Six studies were included, five of which reported on single APT imaging parameters and four of which reported on multiparametric MRI combined with APT imaging parameters. For single APT imaging parameters, the pooled sensitivity and specificity were 0.85 (95% CI: 0.75-0.92) and 0.88 (95% CI: 0.74-0.97). For multiparametric MRI including APT, the pooled sensitivity and specificity were 0.92 (95% CI: 0.85-0.97) and 0.83 (95% CI: 0.55-0.97), respectively. In addition, in the three studies reported on both single and added value of APT imaging parameters, the combined imaging parameters further improved diagnostic performance, yielding pooled sensitivity and specificity of 0.91 (95% CI: 0.80-0.97) and 0.92 (95% CI: 0.79-0.98), respectively, but the pooled sensitivity was 0.81 (95% CI: 0.65-0.93) and specificity was 0.82 (95% CI: 0.61-0.94) for single APT imaging parameters. Conclusion: APT imaging showed high diagnostic performance in assessing treatment response in patients with post-treatment gliomas, and the addition of APT imaging to other advanced MRI techniques can improve the diagnostic accuracy for distinguishing TR from TE.

Brain Perfusion Abnormalities after Radiotherapy Measured by 3-Dimensional Arterial Spin Labeling MRI and Correlations with Cognitive Impairment.

The purpose of this study was to use a 3-dimensional arterial spin labeling (3D ASL) magnetic resonance (MR) method to measure cerebral blood flow (CBF) before and after radiotherapy, and correlate changes with time after receiving radiotherapy and cognitive function. Patients with nasopharyngeal carcinoma receiving radiotherapy at our institution were recruited for the study. Participants were divided into three groups: Pre-radiotherapy control (PC) group, acute reaction period (ARP) group, and delayed reaction period (DRP)group. Thirty-four patients were included in the study. Compared with the PC group, the ARP group exhibited significantly decreased perfusion in the left anterior cingulate cortex (ACC) and right putamen, and increased perfusion in the right cerebellum (Crus 1), right inferior occipital gyrus, left lingual gyrus, left precuneus, and left calcarine gyrus. in the DRP group, increased perfusion was noted in the right cerebellum (Crus 1) and decreased perfusion in the left superior frontal gyrus. CBF differences were observed in several brain areas in the DRP group as compared to the ARP group (P < 0.001). Total Montreal Cognitive Assessment score, and subdomain language and delayed memory recall scores were significantly lower in the ARP and DRP groups than in the PC group (P < 0.05). Data suggest that ASL allows for non-invasive detection of radiation-induced whole-brain CBF changes, which is transient, dynamic and complicated and may be a factor contributing to cognitive impairment induced by radiotherapy for nasopharyngeal carcinoma.

p38-TFEB pathways promote microglia activation through inhibiting CMA-mediated NLRP3 degradation in Parkinson's disease.

BACKGROUND: Parkinson's disease (PD) is characterized by degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc), accompanied by accumulation of α-synuclein, chronic neuroinflammation and autophagy dysfunction. Previous studies suggested that misfolded α-synuclein induces the inflammatory response and autophagy dysfunction in microglial cells. The NLRP3 inflammasome signaling pathway plays a crucial role in the neuroinflammatory process in the central nervous system. However, the relationship between autophagy deficiency and NLRP3 activation induced by α-synuclein accumulation is not well understood. METHODS: Through immunoblotting, immunocytochemistry, immunofluorescence, flow cytometry, ELISA and behavioral tests, we investigated the role of p38-TFEB-NLRP3 signaling pathways on neuroinflammation in the α-synuclein A53T PD models. RESULTS: Our results showed that increased protein levels of NLRP3, ASC, and caspase-1 in the α-synuclein A53T PD models. P38 is activated by overexpression of α-synuclein A53T mutant, which inhibited the master transcriptional activator of autophagy TFEB. And we found that NLRP3 was degraded by chaperone-mediated autophagy (CMA) in microglial cells. Furthermore, p38-TFEB pathways inhibited CMA-mediated NLRP3 degradation in Parkinson's disease. Inhibition of p38 had a protective effect on Parkinson's disease model via suppressing the activation of NLRP3 inflammasome pathway. Moreover, both p38 inhibitor SB203580 and NLRP3 inhibitor MCC950 not only prevented neurodegeneration in vivo, but also alleviated movement impairment in α-synuclein A53T-tg mice model of Parkinson's disease. CONCLUSION: Our research reveals p38-TFEB pathways promote microglia activation through inhibiting CMA-mediated NLRP3 degradation in Parkinson's disease, which could be a potential therapeutic strategy for PD. p38-TFEB pathways promote microglia activation through inhibiting CMA-mediated NLRP3 degradation in Parkinson's disease. In this model, p38 activates NLRP3 inflammasome via inhibiting TFEB in microglia. TFEB signaling negatively regulates NLRP3 inflammasome through increasing LAMP2A expression, which binds to NLRP3 and promotes its degradation via chaperone-mediated autophagy (CMA). NLRP3-mediated microglial activation promotes the death of dopaminergic neurons.

Comparison of percentage changes in quantitative diffusion parameters for assessing pathological complete response to neoadjuvant therapy in locally advanced rectal cancer: a meta-analysis.

PURPOSE: To evaluate and compare the diagnostic performance of percentage changes in apparent diffusion coefficient (∆ADC%) and slow diffusion coefficient (∆D%) for assessing pathological complete response (pCR) to neoadjuvant therapy in patients with locally advanced rectal cancer (LARC). METHODS: A systematic search in PubMed, EMBASE, the Web of Science, and the Cochrane Library was performed to retrieve related original studies. For each parameter (∆ADC% and ∆D%), we pooled the sensitivity, specificity and calculated the area under summary receiver operating characteristic curve (AUROC) values. Meta-regression and subgroup analyses were performed to explore heterogeneity among the studies on ∆ADC%. RESULTS: 15 original studies (804 patients with 805 lesions, 15 studies on ∆ADC%, 4 of the studies both on ∆ADC% and ∆D%) were included. pCR was observed in 213 lesions (26.46%). For the assessment of pCR, the pooled sensitivity, specificity and AUROC of ∆ADC% were 0.83 (95% confidence intervals [CI] 0.76, 0.89), 0.74 (95% CI 0.66, 0.81), 0.87 (95% CI 0.83, 0.89), and ∆D% were 0.70 (95% CI 0.52, 0.84), 0.81 (95% CI 0.65, 0.90), 0.81 (95% CI 0.77, 0.84), respectively. In the four studies on the both metrics, ∆ADC% yielded an equivalent diagnostic performance (AUROC 0.80 [95% CI 0.76, 0.83]) to ∆D%, but lower than in the studies (n = 11) only on ∆ADC% (AUROC 0.88 [95% CI 0.85, 0.91]). Meta-regression and subgroup analyses showed no significant factors affecting heterogeneity. CONCLUSIONS: Our meta-analysis confirms that ∆ADC% could reliably evaluate pCR in patients with LARC after neoadjuvant therapy. ∆D% may not be superior to ∆ADC%, which deserves further investigation.

Targeting Macrophage for the Treatment of Amyotrophic Lateral Sclerosis.

BACKGROUND & OBJECTIVE: Amyotrophic lateral sclerosis is a progressive neurodegenerative disease that specifically affects motor neurons in the brain and in the spinal cord. Patients with amyotrophic lateral sclerosis usually die from respiratory failure within 3 to 5 years from when the symptoms first appear. Currently, there is no cure for amyotrophic lateral sclerosis. Accumulating evidence suggests that dismantling of neuromuscular junction is an early event in the pathogenesis of amyotrophic lateral sclerosis. CONCLUSION: It is starting to realized that macrophage malfunction contributes to the disruption of neuromuscular junction. Modulation of macrophage activation states may stabilize neuromuscular junction and provide protection against motor neuron degeneration in amyotrophic lateral sclerosis.

DRAM1 regulates autophagy and cell proliferation via inhibition of the phosphoinositide 3-kinase-Akt-mTOR-ribosomal protein S6 pathway.

BACKGROUND: Macroautophagy (hereafter autophagy) is a tightly regulated process that delivers cellular components to lysosomes for degradation. Damage-regulated autophagy modulator 1 (DRAM1) induces autophagy and is necessary for p53-mediated apoptosis. However, the signalling pathways regulated by DRAM1 are not fully understood. METHODS: HEK293T cells were transfected with FLAG-DRAM1 plasmid. Autophagic proteins (LC3 and p62), phosphorylated p53 and the phosphorylated proteins of the class I PI3K-Akt-mTOR-ribosomal protein S6 (rpS6) signalling pathway were detected with Western blot analysis. Cellular distribution of DRAM1 was determined with immunostaining. DRAM1 was knocked down in HEK293T cells using siRNA oligos which is confirmed by quantitative RT-PCR. Cells were serum starved for 18 h after overexpression or knockdown of DRAM1 to decrease the rpS6 activity to the basal level, and then the cells were stimulated with insulin growth factor, epidermal growth factor or serum. rpS6 phosphorylation and rpS6 were detected with Western blotting. Similarly, after overexpression or knockdown of DRAM1, phosphorylation of IGF-1Rß and IGF-1R were examined with Western blotting. Cell viability was determined with CCK-8 assay and colony formation assay. Finally, human cancer cells Hela, SW480, and HCT116 were transfected with the FLAG-DRAM1 plasmid and phosphorylated rpS6 and rpS6 were detected with Western blot analysis. RESULTS: DRAM1 induced autophagy and inhibited rpS6 phosphorylation in an mTORC1-dependent manner in HEK293T cells. DRAM1 didn't affect the phosphorylated and total levels of p53. Furthermore, DRAM1 inhibited the activation of the PI3K-Akt pathway stimulated with growth factors or serum. DRAM1 was localized at the plasma membrane and regulate the phosphorylation of IGF-1 receptor. DRAM1 decreased cell viability and colony numbers upon serum starvation. Additionally, DRAM1 inhibited rpS6 phosphorylation in several human cancer cells. CONCLUSIONS: Here we provided evidence that DRAM1 inhibited rpS6 phosphorylation in multiple cell types. DRAM1 inhibited the phosphorylation of Akt and the activation of Akt-rpS6 pathway stimulated with growth factors and serum. Furthermore, DRAM1 regulated the activation of IGF-1 receptor. Thus, our results identify that the class I PI3K-Akt-rpS6 pathway is regulated by DRAM1 and may provide new insight into the potential role of DRAM1 in human cancers.

Mitochondrial calcium dysfunction contributes to autophagic cell death induced by MPP+ via AMPK pathway.

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by the loss of dopaminergic neurons in the substantia nigra. Prevailing evidence suggests that abnormal autophagy and mitochondrial dysfunction participate in the process of PD. However, many damages of neuronal functions are regulated by intracellular Ca2+ signaling and the contribution of mitochondrial Ca2+ to the process of neurodegeneration is still unclear. MPP+, the metabolite of a neurotoxin MPTP, causes symptom of PD in animal models by selectively destroying dopaminergic neurons in substantia nigra. Here we report that mitochondrial Ca2+ uniporter (MCU) participated in MPP+-induced autophagic cell death in SH-SY5Y cells. Pharmacological agonist of MCU or exogenous expressed MCU can partially reduce MPP+-induced autophagic cell death. Down-regulation of MCU enhanced autophagic cell death via AMPK activation, which was independent of Beclin1 and PI3K. These findings show that the mitochondrial calcium dyshomeostasis contributes to MPP+-induced neuronal degeneration, and MCU may be a potential therapeutic target of PD through the prevention of pathological autophagy.

Autophagy in inflammation: the p38α MAPK-ULK1 axis.

Autophagy and inflammation are two processes vital for immune cells to perform their functions. Their proper interplay upon signal is pivotal for proper response to stress. The stress kinase p38α MAPK in microglia senses inflammatory cue LPS, directly phosphorylates ULK1, relieves the autophagic inhibition on the inflammatory machinery, and thus allows for a full immune response.

Release the autophage brake on inflammation: The MAPK14/p38α-ULK1 pedal.

Macroautophagy/autophagy and inflammation are 2 intertwined processes vital for immune cells to perform their functions. Under resting conditions, autophagy acts as a brake to suppress inflammation in microglia. Upon signal stimulation, their fine-tuned interplay is pivotal for proper response to stress. How inflammatory signals remove this autophagy brake on inflammation remains unclear. In a recent study, we showed that the stress kinase MAPK14/p38α in microglia senses the inflammatory cue lipopolysaccharide (LPS), directly phosphorylates and inhibits ULK1, relieves the autophagic inhibition on the inflammatory machinery, and thus allows for a full immune response.

Targeting Chaperone-Mediated Autophagy for Disease Therapy.

PURPOSE OF THE REVIEW: To reason that targeting chaperone-mediated autophagy (CMA) represents a promising approach for disease therapy, we will summarize advances in researches on the relationship between CMA and diseases and discuss relevant strategies for disease therapy by targeting the CMA process. RECENT FINDINGS: CMA is a unique kind of selective autophagy in lysosomes. Under physiological conditions, CMA participates in the maintenance of cellular homeostasis by protein quality control, bioenergetics, and timely regulated specific substrate-associated cellular processes. Under pathological conditions, CMA interplays with various disease conditions. CMA makes adaptive machinery to address stress, while disease-associated proteins alter CMA which is involved in pathogeneses of diseases. As more proteins are identified as CMA substrates and regulators, dysregulation of CMA has been implicated in an increasing number of diseases, while rectifying CMA alteration may be a benefit for these diseases. SUMMARY: Alterations of CMA in diseases mainly including neurodegenerative diseases and many cancers raise the possibility of targeting CMA to recover cellular homeostasis as one potential strategy for therapy of relevant diseases.

p38 MAPK inhibits autophagy and promotes microglial inflammatory responses by phosphorylating ULK1.

Inflammation and autophagy are two critical cellular processes. The relationship between these two processes is complex and includes the suppression of inflammation by autophagy. However, the signaling mechanisms that relieve this autophagy-mediated inhibition of inflammation to permit a beneficial inflammatory response remain unknown. We find that LPS triggers p38α mitogen-activated protein kinase (MAPK)-dependent phosphorylation of ULK1 in microglial cells. This phosphorylation inhibited ULK1 kinase activity, preventing it from binding to the downstream effector ATG13, and reduced autophagy in microglia. Consistently, p38α MAPK activity is required for LPS-induced morphological changes and the production of IL-1ß by primary microglia in vitro and in the brain, which correlates with the p38α MAPK-dependent inhibition of autophagy. Furthermore, inhibition of ULK1 alone was sufficient to promote an inflammatory response in the absence of any overt inflammatory stimulation. Thus, our study reveals a molecular mechanism that enables the initial TLR4-triggered signaling pathway to inhibit autophagy and optimize inflammatory responses, providing new understanding into the mechanistic basis of the neuroinflammatory process.

Phosphorylation of LAMP2A by p38 MAPK couples ER stress to chaperone-mediated autophagy.

Endoplasmic reticulum (ER) and lysosomes coordinate a network of key cellular processes including unfolded protein response (UPR) and autophagy in response to stress. How ER stress is signaled to lysosomes remains elusive. Here we find that ER disturbance activates chaperone-mediated autophagy (CMA). ER stressors lead to a PERK-dependent activation and recruitment of MKK4 to lysosomes, activating p38 MAPK at lysosomes. Lysosomal p38 MAPK directly phosphorylates the CMA receptor LAMP2A at T211 and T213, which causes its membrane accumulation and active conformational change, activating CMA. Loss of ER stress-induced CMA activation sensitizes cells to ER stress-induced death. Neurotoxins associated with Parkinson's disease fully engages ER-p38 MAPK-CMA pathway in the mouse brain and uncoupling it results in a greater loss of SNc dopaminergic neurons. This work identifies the coupling of ER and CMA as a critical regulatory axis fundamental for physiological and pathological stress response.

Study of ATM Phosphorylation by Cdk5 in Neuronal Cells.

The phosphatidylinositol-3-kinase-like kinase ATM (ataxia-telangiectasia mutated) plays a central role in coordinating the DNA damage responses including cell cycle checkpoint control, DNA repair, and apoptosis. Mutations of ATM cause a spectrum of defects ranging from neurodegeneration to cancer predisposition. We previously showed that Cdk5 (cyclin-dependent kinase 5) is activated by DNA damage and directly phosphorylates ATM at serine 794 in postmitotic neurons. Phosphorylation at serine 794 precedes and is required for ATM autophosphorylation at serine 1981, and activates ATM kinase activity. Cdk5-ATM pathway plays a crucial role in DNA damage-induced neuronal injury. This chapter describes protocols used in analyzing ATM phosphorylation by Cdk5 in CGNs (cerebellar granule neurons) and its effects on neuronal survival.

Stress induces p38 MAPK-mediated phosphorylation and inhibition of Drosha-dependent cell survival.

MicroRNAs (miRNAs) regulate the translational potential of their mRNA targets and control many cellular processes. The key step in canonical miRNA biogenesis is the cleavage of the primary transcripts by the nuclear RNase III enzyme Drosha. Emerging evidence suggests that the miRNA biogenic cascade is tightly controlled. However, little is known whether Drosha is regulated. Here, we show that Drosha is targeted by stress. Under stress, p38 MAPK directly phosphorylates Drosha at its N terminus. This reduces its interaction with DiGeorge syndrome critical region gene 8 and promotes its nuclear export and degradation by calpain. This regulatory mechanism mediates stress-induced inhibition of Drosha function. Reduction of Drosha sensitizes cells to stress and increases death. In contrast, increase in Drosha attenuates stress-induced death. These findings reveal a critical regulatory mechanism by which stress engages p38 MAPK pathway to destabilize Drosha and inhibit Drosha-mediated cellular survival.

Oxidation of survival factor MEF2D in neuronal death and Parkinson's disease.

AIMS: Dysfunction of myocyte enhancer factor 2D (MEF2D), a key survival protein and transcription factor, underlies the pathogenic loss of dopaminergic (DA) neurons in Parkinson's disease (PD). Both genetic factors and neurotoxins associated with PD impair MEF2D function in vitro and in animal models of PD. We investigated whether distinct stress conditions target MEF2D via converging mechanisms. RESULTS: We showed that exposure of a DA neuronal cell line to 6-hyroxydopamine (6-OHDA), which causes PD in animals models, led to direct oxidative modifications of MEF2D. Oxidized MEF2D bound to heat-shock cognate protein 70 kDa, the key regulator for chaperone-mediated autophagy (CMA), at a higher affinity. Oxidative stress also increased the level of lysosomal-associated membrane protein 2A (LAMP2A), the rate-limiting receptor for CMA substrate flux, and stimulated CMA activity. These changes resulted in accelerated degradation of MEF2D. Importantly, 6-OHDA induced MEF2D oxidation and increased LAMP2A in the substantia nigra pars compacta region of the mouse brain. Consistently, the levels of oxidized MEF2D were much higher in postmortem PD brains compared with the controls. Functionally, reducing the levels of either MEF2D or LAMP2A exacerbated 6-OHDA-induced death of the DA neuronal cell line. Expression of an MEF2D mutant that is resistant to oxidative modification protected cells from 6-OHDA-induced death. INNOVATION: This study showed that oxidization of survival protein MEF2D is one of the pathogenic mechanisms involved in oxidative stress-induced DA neuronal death. CONCLUSION: Oxidation of survival factor MEF2D inhibits its function, underlies oxidative stress-induced neurotoxicity, and may be a part of the PD pathogenic process.

Activation of transcription factor MEF2D by bis(3)-cognitin protects dopaminergic neurons and ameliorates Parkinsonian motor defects.

Parkinson disease (PD) is characterized by the selective demise of dopaminergic (DA) neurons in the substantial nigra pars compacta. Dysregulation of transcriptional factor myocyte enhancer factor 2D (MEF2D) has been implicated in the pathogenic process in in vivo and in vitro models of PD. Here, we identified a small molecule bis(3)-cognitin (B3C) as a potent activator of MEF2D. We showed that B3C attenuated the toxic effects of neurotoxin 1-methyl-4-phenylpyridinium (MPP(+)) by activating MEF2D via multiple mechanisms. B3C significantly reduced MPP(+)-induced oxidative stress and potentiated Akt to down-regulate the activity of MEF2 inhibitor glycogen synthase kinase 3ß (GSK3ß) in a DA neuronal cell line SN4741. Furthermore, B3C effectively rescued MEF2D from MPP(+)-induced decline in both nucleic and mitochondrial compartments. B3C offered SN4741 cells potent protection against MPP(+)-induced apoptosis via MEF2D. Interestingly, B3C also protected SN4741 cells from wild type or mutant A53T α-synuclein-induced cytotoxicity. Using the in vivo PD model of C57BL/6 mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP), we showed that B3C maintained redox homeostasis, promoted Akt function activity, and restored MEF2D level in midbrain neurons. Moreover, B3C greatly prevented the loss of tyrosine hydroxylase signal in substantial nigra pars compacta DA neurons and ameliorated behavioral impairments in mice treated with MPTP. Collectedly, our studies identified B3C as a potent neuroprotective agent whose effectiveness relies on its ability to effectively up-regulate MEF2D in DA neurons against toxic stress in models of PD in vitro and in vivo.

Neurotoxin-induced selective ubiquitination and regulation of MEF2A isoform in neuronal stress response.

The myocyte enhancer factor 2A-D (MEF2) proteins are members of the MCM1-agamous-deficiens-serum response factor family of transcription factors. Various MEF2 isoform proteins are enriched in neurons and exhibit distinct patterns of expression in different regions of the brain. In neurons, MEF2 functions as a converging factor to regulate many neuronal functions including survival. MEF2 activities are tightly controlled in neurons in response to stress. Whether stress signal may differentially regulate MEF2s remains largely unknown. In this work, we showed that MEF2A, but not MEF2C or MEF2D, was modified by ubiquitination in dopaminergic neuronal cell line SN4741 cells. MEF2A was ubiquitinated at its N'-terminus, and the ubiquitination of MEF2A was first detectable in the nuclear compartment and later in the cytoplasm. Ubiquitination of MEF2A correlated with reduced DNA-binding activity and transcriptional activity. More importantly, disturbing the degradation of ubiquitinated MEF2A through proteasome pathway by neurotoxins known to induce Parkinson's disease features in model animals caused accumulation of ubiquitinated MEF2A, reduced MEF2 activity, and impaired cellular viability. Our work thus provides the first evidence to demonstrate an isoforms-specific regulation of MEF2s by ubiquitination-proteasome pathway in dopaminergic neuronal cell by neurotoxins, suggesting that stress signal and cellular context-dependent dysregulation of MEF2s may underlie the loss of neuronal viability.

Modulation of Neuronal Survival Factor MEF2 by Kinases in Parkinson's Disease.

Parkinson's disease (PD) is the second most common neurodegenerative disorder due to selective death of neurons in the substantia nigra pars compacta. The cause of cell death remains largely unknown. Myocyte enhancer factor 2 (MEF2) is a group of transcriptional factors required to regulate neuronal development, synaptic plasticity, as well as survival. Recent studies show that MEF2 functions are regulated in multiple subcellular organelles and suggest that dysregulation of MEF2 plays essential roles in the pathogenesis of PD. Many kinases associated with transcription, translation, protein misfolding, autophagy, and cellular energy homeostasis are involved in the neurodegenerative process. Following the first demonstration that mitogen-activated protein kinase p38 (p38 MAPK) directly phosphorylates and activates MEF2 to promote neuronal survival, several other kinase regulators of MEF2s have been identified. These include protein kinase A and extracellular signal regulated kinase 5 as positive MEF2 regulators, and cyclin-dependent kinase 5 (Cdk5) and glycogen synthase kinase 3ß as negative regulators in response to diverse toxic signals relevant to PD. It is clear that MEF2 has emerged as a key point where survival and death signals converge to exert their regulatory effects, and dysregulation of MEF2 function in multiple subcellular organelles may underlie PD pathogenesis. Moreover, several other kinases such as leucine-rich repeat kinase 2 and PTEN-induced putative kinase 1 (PINK1) are of particular interest due to their potential interaction with MEF2.

Calpain-mediated degradation of myocyte enhancer factor 2D contributes to excitotoxicity by activation of extrasynaptic N-methyl-D-aspartate receptors.

Synaptic and extrasynaptic NMDA receptors (NMDARs) appear to play opposite roles in neuronal survival and death. Here we report the new findings on the dysregulation of survival factor, myocyte enhancer factor 2D (MEF2D), by extrasynaptic NMDARs. Excitotoxicity led to the NMDAR-dependent degradation of MEF2D protein and inhibition of its transactivation activity in mature cortical neurons. The activation of extrasynaptic NMDARs alone was sufficient for degradation of MEF2D. Calpain directly cleaved MEF2D in vitro and blocking this protease activity greatly attenuated NMDAR signaled degradation of MEF2D in neurons. Consistently, inhibition of calpain protected cortical neurons from NMDA-induced excitotoxicity. Furthermore, knockdown of MEF2D sensitized neurons to NMDA-induced excitotoxicity, which was not protected by calpain inhibition. Collectively, these findings suggest that dysregulation of MEF2D by calpain may mediate excitotoxicity via an extrasynaptic NMDAR-dependent manner.