Role for the ubiquitin-proteasome system in Parkinson’s disease and other neurodegenerative brain amyloidoses

Many neurodegenerative brain amyloidoses, including Alzheimer’s and Parkinson’s disease, are characterized by selective neuronal loss together with the appearance of intraneuronal ubiquitin-positive proteinaceous aggregates or inclusion bodies. These features usually result from the abnormal accumulation and processing of mutant, misfolded, or damaged intracellular proteins. It has recently become clear that both genetic factors and aberrant proteolytic degradation may therefore play a major role in neuronal degeneration. Indeed, the linkage of two genes directly involved in the ubiquitin-proteasome system (UPS) in familial Parkinson’s disease clearly indicates a central role for the UPS in neurodegeneration, and thus Parkinson’s disease is considered the prototypical disorder associated with UPS dysfunction. In this review, we provide an overview of the key genes / proteins implicated in the abnormal UPS-mediated proteolytic processing of unwanted proteins observed in neurodegenerative brain amyloidoses. We also provide an outline of the various components and pathways involved in the normal cellular functioning of the UPS and discuss the mechanisms by which UPS dysfunction can compromise neuronal integrity. A more complete understanding of the UPS and its relationship to the neurodegenerative process will undoubtedly provide tremendous insight into the molecular pathogenesis of amyloidogenic neurodegenerative disorders and will allow the development of novel rational therapies for treating these disorders.     

Targeting autophagy and mitophagy for mitochondrial diseases treatment

Introduction: Mitochondrial diseases are a group of rare genetic diseases with complex and heterogeneous origins which manifest a great variety of phenotypes. Disruption of the oxidative phosphorylation system is the main cause of pathogenicity in mitochondrial diseases since it causes accumulation of reactive oxygen species (ROS) and ATP depletion.

Areas covered: Current evidences support the main protective role of autophagy and mitophagy in mitochondrial diseases and other diseases associated with mitochondrial dysfunction.

Expert Opinion: The use of autophagy and/or mitophagy inducers may allow a novel strategy for improving mitochondrial function for both mitochondrial diseases and other diseases with altered mitochondrial metabolism. However, a deeper investigation of the molecular mechanisms behind mitophagy and mitochondrial biogenesis is needed in order to safely modulate these processes. In the coming years, we will also see an increase in awareness of mitochondrial dynamics modulation that will allow the therapeutic use of new drugs for improving mitochondrial function in a great variety of mitochondrial disorders.     

小檗碱对心肌缺血再灌注损伤大鼠线粒体自噬及对PINK1/Parkin通路的影响

目的 探讨小檗碱对心肌缺血再灌注损伤大鼠线粒体自噬及PTEN诱导激酶1(PTEN induced putative kinase 1,PINK1)/帕金森病蛋白(Parkin)通路的影响.方法 建立心肌缺血再灌注损伤大鼠模型,随机分组为模型组、小檗碱低、高剂量(75、150 mg/kg)组,自噬抑制剂三甲基腺嘌呤(3-...     

Histone deacetylase inhibitors inhibit cervical cancer growth through Parkin acetylation-mediated mitophagy

Parkin, an E3 ubiquitin ligase, plays a role in maintaining mitochondrial homeostasis through targeting damaged mitochondria for mitophagy. Accumulating evidence suggests that the acetylation modification of the key mitophagy machinery influences mitophagy level, but the underlying mechanism is poorly understood. Here, our study demonstrated that inhibition of histone deacetylase (HDAC) by treatment of HDACis activates mitophagy through mediating Parkin acetylation, leading to inhibition of cervical cancer cell proliferation. Bioinformatics analysis shows that Parkin expression is inversely correlated with HDAC2 expression in human cervical cancer, indicating the low acetylation level of Parkin. Using mass spectrometry, Parkin is identified to interact with two upstream molecules, acetylase acetyl-CoA acetyltransferase 1 (ACAT1) and deacetylase HDAC2. Under treatment of suberoylanilide hydroxamic acid (SAHA), Parkin is acetylated at lysine residues 129, 220 and 349, located in different domains of Parkin protein. In in vitro experiments, combined mutation of Parkin largely attenuate the interaction of Parkin with PTEN induced putative kinase 1 (PINK1) and the function of Parkin in mitophagy induction and tumor suppression. In tumor xenografts, the expression of mutant Parkin impairs the tumor suppressive effect of Parkin and decreases the anticancer activity of SAHA. Our results reveal an acetylation-dependent regulatory mechanism governing Parkin in mitophagy and cervical carcinogenesis, which offers a new mitophagy modulation strategy for cancer therapy.     

Parkin基因结构功能及其表达与帕金森病

Parkin基因是与帕金森病关系最为密切的基因,对其结构、功能及其表达各方面研究也越来越多,尤其是表观遗传调控机制的提出,为我们从另一角度理解帕金森病提供了重要线索。本文从Parkin基因的结构、功能及其表达对Parkin基因进行了详细的阐述,并试述了其甲基化的可能性。     

Parkin is an E3 ubiquitin-ligase for normal and mutant ataxin-2 and prevents ataxin-2-induced cell death

Expansion of the polyQ repeat in ataxin-2 results in degeneration of Purkinje neurons and other neuronal groups including the substantia nigra in patients with spinocerebellar ataxia type 2 (SCA2). In animal and cell models, overexpression of mutant ataxin-2 induces cell dysfunction and death, but little is known about steady-state levels of normal and mutant ataxin-2 and cellular mechanisms regulating their abundance. Based on preliminary findings that ataxin-2 interacted with parkin, an E3 ubiquitin ligase mutated in an autosomal recessive form of Parkinsonism, we sought to determine whether parkin played a role in regulating the steady-state levels of ataxin-2. Parkin interacted with the N-terminal half of normal and mutant ataxin-2, and ubiquitinated the full-length form of both wild-type and mutant ataxin-2. Parkin also regulated the steady-state levels of endogenous ataxin-2 in PC12 cells with regulatable parkin expression. Parkin reduced abnormalities in Golgi morphology induced by mutant ataxin-2 and decreased ataxin-2 induced cytotoxicity. In brains of SCA2 patients, parkin labeled cytoplasmic ataxin-2 aggregates in Purkinje neurons. These studies suggest a role for parkin in regulating the intracellular levels of both wild-type and mutant ataxin-2, and in rescuing cells from ataxin-2-induced cytotoxicity. The role of parkin variants in modifying the SCA2 phenotype and its use as a therapeutic target should be further investigated.     

Overexpression of Septin 4, the Drosophila homologue of human CDCrel-1, is toxic for dopaminergic neurons

parkin loss-of-function mutations are linked to autosomal recessive juvenile parkinsonism. Parkin is an E3 ubiquitin ligase that promotes degradation of specific target proteins by the proteasome. It has been proposed that loss of Parkin activity will result in accumulation of its substrates, thus leading to dopaminergic (DA) neuron death. In Drosophila, parkin mutations cause degeneration of a subset of DA neurons in the brain but no Parkin substrates have yet been described. Here we characterized the septin 4 gene, which encodes the Drosophila orthologue of human CDCrel-1, a Parkin substrate. We showed that Septin 4 overexpression causes age-dependent disruption of DA neuron integrity in the dorsomedial cluster, which is suppressed by coexpression of Parkin and enhanced by reducing parkin function. Furthermore, other phenotypes caused by Septin 4 overexpression are also enhanced in a heterozygous parkin mutant background. This indicates that Septin 4 accumulation is toxic for DA neurons and suggests that Septin 4 could be a genuine substrate of Drosophila Parkin. Regarding this, we also showed that both proteins are able to interact physically with each other in vitro, thus supporting this hypothesis.     

Ablation of Akt2 and AMPKα2 rescues high fat diet-induced obesity and hepatic steatosis through Parkin-mediated mitophagy

Given the opposing effects of Akt and AMP-activated protein kinase (AMPK) on metabolic homeostasis, this study examined the effects of deletion of Akt2 and AMPKα2 on fat diet-induced hepatic steatosis. Akt2–Ampkα2 double knockout (DKO) mice were placed on high fat diet for 5 months. Glucose metabolism, energy homeostasis, cardiac function, lipid accumulation, and hepatic steatosis were examined. DKO mice were lean without anthropometric defects. High fat intake led to adiposity and decreased respiratory exchange ratio (RER) in wild-type (WT) mice, which were ablated in DKO but not Akt2^−/− and Ampkα2^−/− mice. High fat intake increased blood and hepatic triglycerides and cholesterol, promoted hepatic steatosis and injury in WT mice. These effects were eliminated in DKO but not Akt2^−/− and Ampkα2^−/− mice. Fat diet promoted fat accumulation, and enlarged adipocyte size, the effect was negated in DKO mice. Fat intake elevated fatty acid synthase (FAS), carbohydrate-responsive element-binding protein (CHREBP), sterol regulatory element-binding protein 1 (SREBP1), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), peroxisome proliferator-activated receptor-α (PPARα), PPARγ, stearoyl-CoA desaturase 1 (SCD-1), phosphoenolpyruvate carboxykinase (PEPCK), glucose 6-phosphatase (G6Pase), and diglyceride O-acyltransferase 1 (DGAT1), the effect was absent in DKO but not Akt2^−/− and Ampkα2^−/− mice. Fat diet dampened mitophagy, promoted inflammation and phosphorylation of forkhead box protein O1 (FoxO1) and AMPKα1 (Ser⁴⁸⁵), the effects were eradicated by DKO. Deletion of Parkin effectively nullified DKO-induced metabolic benefits against high fat intake. Liver samples from obese humans displayed lowered microtubule-associated proteins 1A/1B light chain 3B (LC3B), Pink1, Parkin, as well as enhanced phosphorylation of Akt, AMPK (Ser⁴⁸⁵), and FoxO1, which were consolidated by RNA sequencing (RNAseq) and mass spectrometry analyses from rodent and human livers. These data suggest that concurrent deletion of Akt2 and AMPKα2 offers resilience to fat diet-induced obesity and hepatic steatosis, possibly through preservation of Parkin-mediated mitophagy and lipid metabolism.     

针刺对运动性骨骼肌损伤大鼠骨骼肌线粒体自噬的影响

目的:通过观察针刺对大负荷运动大鼠骨骼肌线粒体自噬相关蛋白表达的影响,探讨针刺在运动性骨骼肌损伤修复中的作用及其机制。方法:将128只成年雄性Sprague-Dawley大鼠随机分为4组:空白对照(control,C;n=8)组、单纯运动(exercise,E;n=40)组、单纯针刺(acupuncture,A;n=40)组和运动针刺(exercise and acupuncture,EA;n=40)组。其中,E和EA组进行1次下坡跑运动,A组和EA组(运动后即刻)施加针刺处理。后3组根据干预后不同时相又分为0 h、12 h、24 h、48 h和72 h亚组(n=8),分别于对应时点分离比目鱼肌进行检测,使用透射电子显微镜观察骨骼肌线粒体超微结构变化;采用ELISA法检测比目鱼肌线粒体定量酶柠檬酸合成酶(CS)的含量变化;应用Western blot法检测骨骼肌PTEN诱导假定激酶1(PINK1)、parkin和微管相关蛋白1轻链3(LC3)的蛋白表达变化。结果:1次大负荷运动后大鼠比目鱼肌线粒体出现明显肿胀和肌膜下积聚等超微结构异常变化,伴有大量自噬体形成;同时CS的含量明显减少(P0.05);线粒体自噬蛋白PINK1、parkin和LC3均出现一过性的表达升高(P0.05)。运动后针刺明显改善了线粒体超微结构的异常变化,减少自噬溶酶体的出现,同时抑制CS的含量减少,下调PINK1、parkin和LC3在线粒体上的表达(P0.05)。结论:1次大负荷运动后骨骼肌线粒体结构和数量受损,通过激活PINK1/parkin途径诱发线粒体自噬的过度发生。大负荷运动后针刺可以缓解骨骼肌线粒体的损伤,其作用机制可能是通过下调线粒体外膜蛋白PINK1表达,抑制其对下游胞浆蛋白parkin的招募,进而影响LC3与线粒体的结合以抑制线粒体自噬过度激活。