Regulation of Parkin expression as the key balance between neural survival and cancer cell death

Protein modification in neurodegenerative diseases

Posttranslational modifications play a crucial role in governing cellular functions and protein behavior. Researchers have implicated dysregulated posttranslational modifications in protein misfolding, which results in cytotoxicity, particularly in neurodegenerative diseases such as Alzheimer disease, Parkinson disease, and Huntington disease. These aberrant posttranslational modifications cause proteins to gather in certain parts of the brain that are linked to the development of the diseases. This leads to neuronal dysfunction and the start of neurodegenerative disease symptoms. Cognitive decline and neurological impairments commonly manifest in neurodegenerative disease patients, underscoring the urgency of comprehending the posttranslational modifications' impact on protein function for targeted therapeutic interventions. This review elucidates the critical link between neurodegenerative diseases and specific posttranslational modifications, focusing on Tau, APP, α-synuclein, Huntingtin protein, Parkin, DJ-1, and Drp1. By delineating the prominent aberrant posttranslational modifications within Alzheimer disease, Parkinson disease, and Huntington disease, the review underscores the significance of understanding the interplay among these modifications. Emphasizing 10 key abnormal posttranslational modifications, this study aims to provide a comprehensive framework for investigating neurodegenerative diseases holistically. The insights presented herein shed light on potential therapeutic avenues aimed at modulating posttranslational modifications to mitigate protein aggregation and retard neurodegenerative disease progression.

Sodium butyrate ameliorates high glucose-suppressed neuronal mitophagy by restoring PRKN expression via inhibiting the RELA-HDAC8 complex

Damaged mitochondria accumulation in diabetes is one of the main features that contribute to increased incidence of cognitive impairment by inducing apoptosis. Butyrate is a major metabolite produced by microbiota that has neuroprotective effects by regulating mitochondrial function. However, detailed mechanisms underlying how butyrate can regulate neuronal mitophagy remain unclear. Here, we examined the regulatory effects of sodium butyrate (NaB) on high glucose-induced mitophagy dysregulation, neuronal apoptosis, and cognitive impairment and its underlying mechanisms in human-induced pluripotent stem cell-derived neurons, SH-SY5Ys, and streptozotocin (STZ)-induced diabetic mice. In our results, diabetic mice showed gut-microbiota dysbiosis, especially a decreased number of butyrate-producing bacteria and reduced NaB plasma concentration. NaB ameliorated high glucose-induced neuronal mitochondrial dysfunction by recovering PRKN/Parkin-mediated mitophagy. High glucose-induced reactive oxygen species (ROS) and -inhibited PRKAA/AMPKα stimulated the RELA/p65-HDAC8 complex, which downregulated PRKN protein expression by binding to the PRKN promoter region. NaB restored PRKN expression by blocking RELA nuclear translocation and directly inhibiting HDAC8 in the nucleus. In addition, HDAC8 overexpression inhibited the positive effect of NaB on high glucose-induced mitophagy dysfunction and neuronal apoptosis. Oral administration of NaB improved cognitive impairment in diabetic mice by restoring mitophagy in the hippocampus. Taken together, NaB ameliorates neuronal mitophagy through PRKN restoration by inhibiting RELA-HDAC8 complexes, suggesting that NaB is an important substance for protecting neuronal apoptosis in diabetes-associated cognitive impairment.

2,3,7,8-Tetrachlorodibenzo-p-dioxin and kynurenine induce Parkin expression in neuroblastoma cells through different signaling pathways mediated by the aryl hydrocarbon receptor

Parkin regulates protein degradation and mitophagy in dopaminergic neurons. Deficiencies in Parkin expression or function lead to cellular stress, cell degeneration, and the death of dopaminergic neurons, which promotes Parkinson's disease. In contrast, Parkin overexpression promotes neuronal survival. Therefore, the mechanisms of Parkin upregulation are crucial to understand. We describe here the molecular mechanism of AHR-mediated Parkin regulation in human SH-SY5Y neuroblastoma cells. Specifically, we report that the human Parkin gene (PRKN) is transcriptionally upregulated by the aryl hydrocarbon receptor (AHR) through two different selective ligand-dependent pathways. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a stress-inducing AHR ligand, indirectly promotes PRKN transcription by inducing ATF4 expression via TCDD-mediated endoplasmic reticulum (ER) stress. In contrast, kynurenine, a nontoxic AHR agonist, induces PRKN transcription by promoting AHR binding to the PRKN promoter without activating ER stress. Our results demonstrate that AHR activation may be a potential pharmacological pathway to induce human Parkin, but such a strategy must carefully consider the choice of AHR ligand to avoid neurotoxic side effects.

Single-cell and spatial transcriptomics reveals that PTPRG activates the m6A methyltransferase VIRMA to block mitophagy-mediated neuronal death in Alzheimer's disease

Neuronal death is one of the key pathologies in Alzheimer's disease (AD). How neuronal death begins in AD is far from clear, so clarifying this process may help develop effective therapies. This study collected single-cell RNA sequencing data of 85 AD samples and 83 control samples, covering the prefrontal cortex, internal olfactory cortex, superior parietal lobe, superior frontal gyrus, caudal internal olfactory cortex, somatosensory cortex, hippocampus, superior frontal cortex and peripheral blood mononuclear cells. Additionally, spatial transcriptomic data of coronal sections from 6 AppNL-G-F AD mice and 6 control C57Bl/6 J mice were acquired. The main single-cell and spatial transcriptomics results were experimentally validated in wild type and 5 × FAD mice. We found that the microglia subpopulation Mic_PTPRG can communicate with specific types of neurons (especially excitatory ExNeu_PRKN_VIRMA and inhibitory InNeu_PRKN_VIRMA neuronal subpopulations) and cause them to express PTPRG during AD progression. Within neurons, PTPRG binds and upregulates the m6A methyltransferase VIRMA, thus inhibiting translation of PRKN mRNA to prevent the clearance of damaged mitochondria in neurons through suppressing mitophagy. As the disease progresses, the energy and nutrient metabolic pathways in neurons are reprogrammed, leading to their death. Consistently, we determined that PTPTRG can physically interact with VIRMA in mouse brains and PRKN is significantly upregulated in 5 × FAD mouse brain. Altogether, our findings demonstrate that PTPRG activates the m6A methyltransferase VIRMA to block mitophagy-mediated neuronal death in AD, which is a potential pathway, through which microglia and neuronal PTPRG modify neuronal connections in the brain during AD progression.

Parkin inhibits proliferation and migration of bladder cancer via ubiquitinating Catalase

PRKN is a key gene involved in mitophagy in Parkinson's disease. However, recent studies have demonstrated that it also plays a role in the development and metastasis of several types of cancers, both in a mitophagy-dependent and mitophagy-independent manner. Despite this, the potential effects and underlying mechanisms of Parkin on bladder cancer (BLCA) remain unknown. Therefore, in this study, we investigated the expression of Parkin in various BLCA cohorts derived from human. Here we show that PRKN expression was low and that PRKN acts as a tumor suppressor by inhibiting the proliferation and migration of BLCA cells in a mitophagy-independent manner. We further identified Catalase as a binding partner and substrate of Parkin, which is an important antioxidant enzyme that regulates intracellular ROS levels during cancer progression. Our data showed that knockdown of CAT led to increased intracellular ROS levels, which suppressed cell proliferation and migration. Conversely, upregulation of Catalase decreased intracellular ROS levels, promoting cell growth and migration. Importantly, we found that Parkin upregulation partially restored these effects. Moreover, we discovered that USP30, a known Parkin substrate, could deubiquitinate and stabilize Catalase. Overall, our study reveals a novel function of Parkin and identifies a potential therapeutic target in BLCA.

Hydrogen peroxide activates APE1/Ref-1 via NF-κB and Parkin: A role in liver cancer resistance to oxidative stress

Cancer cells exhibit an altered redox balance and aberrant redox signaling due to genetic, metabolic, and microenvironment-associated reprogramming. Persistently elevated levels of reactive oxygen species (ROS) contribute to many aspects of tumor development and progression. Emerging studies demonstrated the vital role of apurinic/apyrimidinic endonuclease 1 or reduction/oxidation (redox) factor 1(APE1/Ref-1) in the oxidative stress response and survival of cancer cells. APE1/Ref-1 is a multifunctional enzyme involved in the DNA damage response and functions as a redox regulator of transcription factors. We herein demonstrated that basal hydrogen peroxide (H₂O₂) and APE1/Ref-1 expression levels were markedly higher in cancer cell lines than in non-cancerous cells. Elevated APE1/Ref-1 levels were associated with shorter survival in liver cancer patients. Mechanistically, we showed that H₂O₂ activated nuclear factor-κB (NF-κB). RelA/p65 inhibited the expression of the E3 ubiquitin ligase Parkin, possibly by interfering with ATF4 activity. Parkin was responsible for the ubiquitination and proteasomal degradation of APE1/Ref-1; therefore, the H₂O₂-induced suppression of Parkin expression increased APE1/Ref-1 levels. The probability of survival was lower in liver cancer patients with low Parkin and high RelA expression levels. Additionally, Parkin and RelA expression levels negatively and positively correlated with APE1/Ref-1 levels, respectively, in the TCGA liver cancer cohort. We concluded that increases in APE1/Ref-1 via the NF-κB and Parkin pathways are critical for cancer cell survival under oxidative stress. The present results show the potential of the NF-κB-Parkin-APE1/Ref-1 axis as a prognostic factor and therapeutic strategy to eradicate liver cancer.

Interaction of a Novel Alternatively Spliced Variant of HSD11B1L with Parkin Enhances the Carcinogenesis Potential of Glioblastoma: Peiminine Interferes with This Interaction

Glioblastoma (GBM) is a primary brain tumor of unknown etiology. It is extremely aggressive, incurable and has a short average survival time for patients. Therefore, understanding the precise molecular mechanisms of this diseases is essential to establish effective treatments. In this study, we cloned and sequenced a splice variant of the hydroxysteroid 11-β dehydrogenase 1 like gene (HSD11B1L) and named it HSD11B1L-181. HSD11 B1L-181 was specifically expressed only in GBM cells. Overexpression of this variant can significantly promote the proliferation, migration and invasion of GBM cells. Knockdown of HSD11B1L-181 expression inhibited the oncogenic potential of GBM cells. Furthermore, we identified the direct interaction of parkin with HSD11B1L-181 by screening the GBM cDNA expression library via yeast two-hybrid. Parkin is an RBR E3 ubiquitin ligase whose mutations are associated with tumorigenesis. Small interfering RNA treatment of parkin enhanced the proliferative, migratory and invasive abilities of GBM. Finally, we found that the alkaloid peiminine from the bulbs of Fritillaria thunbergii Miq blocks the interaction between HSD11B1L-181 and parkin, thereby lessening carcinogenesis of GBM. We further confirmed the potential of peiminine to prevent GBM in cellular, ectopic and orthotopic xenograft mouse models. Taken together, these findings not only provide insight into GBM, but also present an opportunity for future GBM treatment.

Control of Mitochondrial Activity by the Ubiquitin Code in Health and Cancer

Cellular homeostasis is tightly connected to the broad variety of mitochondrial functions. To stay healthy, cells need a constant supply of nutrients, energy production and antioxidants defenses, undergoing programmed death when a serious, irreversible damage occurs. The key element of a functional integration of all these processes is the correct crosstalk between cell signaling and mitochondrial activities. Once this crosstalk is interrupted, the cell is not able to communicate its needs to mitochondria, resulting in oxidative stress and development of pathological conditions. Conversely, dysfunctional mitochondria may affect cell viability, even in the presence of nutrients supply and energy production, indicating the existence of feed-back control mechanisms between mitochondria and other cellular compartments. The ubiquitin proteasome system (UPS) is a multi-step biochemical pathway that, through the conjugation of ubiquitin moieties to specific protein substrates, controls cellular proteostasis and signaling, removing damaged or aged proteins that might otherwise accumulate and affect cell viability. In response to specific needs or changed extracellular microenvironment, the UPS modulates the turnover of mitochondrial proteins, thus influencing the organelle shape, dynamics and function. Alterations of the dynamic and reciprocal regulation between mitochondria and UPS underpin genetic and proliferative disorders. This review focuses on the mitochondrial metabolism and activities supervised by UPS and examines how deregulation of this control mechanism results in proliferative disorders and cancer.

The ubiquitin E3 ligase Parkin regulates neuronal CaV1.3 channel functional expression

Neuronal L-type Ca²⁺ channels of the Ca_V1.3 subclass are transmembrane protein complexes that contribute to the pacemaker activity in the adult substantia nigra dopaminergic neurons. The altered function of these channels may play a role in the development and progress of neurodegenerative mechanisms implicated in Parkinson's disease (PD). Although L-type channel expression is precisely regulated, an increased functional expression has been observed in PD. Previously, we showed that Parkin, an E3 enzyme of the ubiquitin-proteasome system (UPS) interacts with neuronal Ca_V2.2 channels promoting their ubiquitin-mediated degradation. In addition, previous studies show an increase in Ca_V1.3 channel activity in dopaminergic neurons of the SNc and that Parkin expression is reduced in PD. These findings suggest that the decrease in Parkin may affect the proteasomal degradation of Ca_V1.3, which helps explain the increase in channel activity. Therefore, the present report aims to gain insight into the degradation mechanisms of the neuronal Ca_V1.3 channel by the UPS. Immunoprecipitation assays showed the interaction between Parkin and the Ca_V1.3 channels expressed in HEK-293 cells and neural tissues. Likewise, Parkin overexpression reduced the total and membrane channel levels and decreased the current density. Consistent with this, patch-clamp recordings in the presence of an inhibitor of the UPS, MG132, prevented the effects of Parkin, suggesting enhanced channel proteasomal degradation. In addition, the half-life of the pore-forming Ca_V1.3α₁ protein was significantly reduced by Parkin overexpression. Finally, electrophysiological recordings using a PRKN knockout HEK-293 cell line generated by CRISPR/Cas9 showed increased current density. These results suggest that Parkin promotes the proteasomal degradation of Ca_V1.3, which may be a relevant aspect for the pathophysiology of PD.NEW & NOTEWORTHY The increased expression of Ca_V1.3 calcium channels is a crucial feature of Parkinson's disease (PD) pathophysiology. However, the mechanisms that determine this increase are not yet defined. Parkin, an enzyme of the ubiquitin-proteasome system, is known to interact with neuronal channels promoting their ubiquitin-mediated degradation. Interestingly, Parkin mutations also play a role in PD. Here, the degradation mechanisms of Ca_V1.3 channels and their relationship with the pathophysiology of PD are studied in detail.

The role of vitamin D on redox regulation and cellular senescence

Vitamin D is considered an essential micronutrient for human health that is metabolized into a multifunctional secosteroid hormone. We can synthesize it in the skin through ultraviolet B (UVB) rays or acquire it from the diet. Its deficiency is a major global health problem that affects all ages and ethnic groups. Furthermore, dysregulation of vitamin D homeostasis has been associated with premature aging, driven by various cellular processes, including oxidative stress and cellular senescence. Various studies have shown that vitamin D can attenuate oxidative stress and delay cellular senescence, mainly by inducing the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and Klotho and improving mitochondrial homeostasis, proposing this vitamin as an excellent candidate for delaying aging. However, the mechanisms around these processes are not yet fully explored. Therefore, in this review, the effects of vitamin D on redox regulation and cellular senescence are discussed to propose new lines of research and clinical applications of vitamin D in the context of age-related diseases.

Does the Expression and Epigenetics of Genes Involved in Monogenic Forms of Parkinson’s Disease Influence Sporadic Forms?

Parkinson’s disease (PD) is a disorder characterized by a triad of motor symptoms (akinesia, rigidity, resting tremor) related to loss of dopaminergic neurons mainly in the Substantia nigra pars compacta. Diagnosis is often made after a substantial loss of neurons has already occurred, and while dopamine replacement therapies improve symptoms, they do not modify the course of the disease. Although some biological mechanisms involved in the disease have been identified, such as oxidative stress and accumulation of misfolded proteins, they do not explain entirely PD pathophysiology, and a need for a better understanding remains. Neurodegenerative diseases, including PD, appear to be the result of complex interactions between genetic and environmental factors. The latter can alter gene expression by causing epigenetic changes, such as DNA methylation, post-translational modification of histones and non-coding RNAs. Regulation of genes responsible for monogenic forms of PD may be involved in sporadic PD. This review will focus on the epigenetic mechanisms regulating their expression, since these are the genes for which we currently have the most information available. Despite technical challenges, epigenetic epidemiology offers new insights on revealing altered biological pathways and identifying predictive biomarkers for the onset and progression of PD.

Epigenetics of Mitochondria-Associated Genes in Striated Muscle

Striated muscle has especially large energy demands. We identified 97 genes preferentially expressed in skeletal muscle and heart, but not in aorta, and found significant enrichment for mitochondrial associations among them. We compared the epigenomic and transcriptomic profiles of the 27 genes associated with striated muscle and mitochondria. Many showed strong correlations between their tissue-specific transcription levels, and their tissue-specific promoter, enhancer, or open chromatin as well as their DNA hypomethylation. Their striated muscle-specific enhancer chromatin was inside, upstream, or downstream of the gene, throughout much of the gene as a super-enhancer (CKMT2, SLC25A4, and ACO2), or even overlapping a neighboring gene (COX6A2, COX7A1, and COQ10A). Surprisingly, the 3' end of the 1.38 Mb PRKN (PARK2) gene (involved in mitophagy and linked to juvenile Parkinson's disease) displayed skeletal muscle/myoblast-specific enhancer chromatin, a myoblast-specific antisense RNA, as well as brain-specific enhancer chromatin. We also found novel tissue-specific RNAs in brain and embryonic stem cells within PPARGC1A (PGC-1α), which encodes a master transcriptional coregulator for mitochondrial formation and metabolism. The tissue specificity of this gene's four alternative promoters, including a muscle-associated promoter, correlated with nearby enhancer chromatin and open chromatin. Our in-depth epigenetic examination of these genes revealed previously undescribed tissue-specific enhancer chromatin, intragenic promoters, regions of DNA hypomethylation, and intragenic noncoding RNAs that give new insights into transcription control for this medically important set of genes.