Constitutive silencing of LRRK2 kinase activity leads to early glucocerebrosidase deregulation and late impairment of autophagy in vivo

Puerarin enhances TFEB-mediated autophagy and attenuates ROS-induced pyroptosis after ischemic injury of random-pattern skin flaps

BACKGROUND AND AIM

Necrosis of random-pattern flaps restricts their application in clinical practice. Puerarin has come into focus due to its promising therapeutic effects in ischemic diseases. Here, we employed Puerarin and investigated its role and potential mechanisms in flap survival.

EXPERIMENTAL PROCEDURE

The effect of Puerarin on the viability of human umbilical vein endothelial cells (HUVECs) was assessed by CCK-8, EdU staining, migration, and scratch assays. Survival area measurement and laser Doppler blood flow (LDBF) were utilized to assess the viability of ischemic injury flaps. Levels of molecules related to oxidative stress, pyroptosis, autophagy, transcription factor EB (TFEB), and the AMPK-TRPML1-Calcineurin signaling pathway were detected using western blotting, immunofluorescence, dihydroethidium (DHE) staining, RT-qPCR and Elisa.

KEY RESULTS

The findings demonstrated that Puerarin enhanced the survivability of ischemic flaps. Autophagy, oxidative stress, and pyroptosis were implicated in the ability of Puerarin in improving flap survival. Increased autophagic flux and augmented tolerance to oxidative stress contribute to Puerarin's suppression of pyroptosis. Additionally, Puerarin modulated the activity of TFEB through the AMPK-TRPML1-Calcineurin signaling pathway, thereby enhancing autophagic flux.

CONCLUSIONS AND IMPLICATIONS

Puerarin promoted flap survival from ischemic injury through upregulation of TFEB-mediated autophagy and inhibition of oxidative stress. Our findings offered valuable support for the clinical application of Puerarin in the treatment of ischemic diseases, including random-pattern flaps.

TIGAR exacerbates obesity by triggering LRRK2-mediated defects in macroautophagy and chaperone-mediated autophagy in adipocytes

Obesity is one of the most common metabolic diseases around the world, which is distinguished by the abnormal buildup of triglycerides within adipose cells. Recent research has revealed that autophagy regulates lipid mobilization to maintain energy balance. TIGAR (Trp53 induced glycolysis regulatory phosphatase) has been identified as a glycolysis inhibitor, whether it plays a role in the metabolism of lipids is unknown. Here, we found that TIGAR transgenic (TIGAR+/+) mice exhibited increased fat mass and trended to obesity phenotype. Non-target metabolomics showed that TIGAR caused the dysregulation of the metabolism profile. The quantitative transcriptome sequencing identified an increased levels of LRRK2 and RAB7B in the adipose tissue of TIGAR+/+ mice. It was confirmed in vitro that TIGAR overexpression increased the levels of LRRK2 by inhibiting polyubiquitination degradation, thereby suppressing macroautophagy and chaperone-mediated autophagy (CMA) while increasing lipid accumulation which were reversed by the LRRK2 inhibitor DNL201. Furthermore, TIGAR drove LRRK2 to interact with RAB7B for suppressing lysosomal degradation of lipid droplets, while the increased lipid droplets in adipocytes were blocked by the RAB7B inhibitor ML282. Additionally, fat-specific TIGAR knockdown of TIGAR+/+ mice alleviated the symptoms of obesity, and adipose tissues-targeting superiority DNL201 nano-emulsion counteracted the obesity phenotype in TIGAR+/+ mice. In summary, the current results indicated that TIGAR performed a vital function in the lipid metabolism through LRRK2-mediated negative regulation of macroautophagy and CMA in adipocyte. The findings suggest that TIGAR has the potential to serve as a viable therapeutic target for treating obesity and its associated metabolic dysfunction.

Genomic profile of Parkinson's disease in Asians

Parkinson's Disease (PD) has witnessed an alarming rise in prevalence, highlighting the suboptimal nature of early diagnostic and therapeutic strategies. To address this issue, genetic testing has emerged as a potential avenue. In this comprehensive review, we have meticulously summarized the variants associated with PD in Asian populations. Our review reveals that these variants exert their influence on diverse biological pathways, encompassing the autophagy-lysosome pathway, cholesterol metabolism, circadian rhythm regulation, immune system response, and synaptic function. Conventionally, PD has been linked to other diseases; however, our findings shed light on a shared genetic susceptibility among these conditions, implying an underlying pathophysiological mechanism that unifies them. Moreover, it is noteworthy that these PD-associated variants can significantly impact drug responses during therapeutic interventions. This review not only provides a consolidated overview of the genetic variants associated with PD in Asian populations but also contributes novel insights into the intricate relationships between PD and other diseases by elucidating shared genetic components. These findings underscore the importance of personalized approaches in diagnosing and treating PD based on individual genetic profiles to optimize patient outcomes.

Autophagy in Parkinson's Disease

Parkinson's disease (PD) is a devastating disease associated with accumulation of α-synuclein (α-Syn) within dopaminergic neurons, leading to neuronal death. PD is characterized by both motor and non-motor clinical symptoms. Several studies indicate that autophagy, an important intracellular degradation pathway, may be involved in different neurodegenerative diseases including PD. The autophagic process mediates the degradation of protein aggregates, damaged and unneeded proteins, and organelles, allowing their clearance, and thereby maintaining cell homeostasis. Impaired autophagy may cause the accumulation of abnormal proteins. Incomplete or impaired autophagy may explain the neurotoxic accumulation of protein aggregates in several neurodegenerative diseases including PD. Indeed, studies have suggested the contribution of impaired autophagy to α-Syn accumulation, the death of dopaminergic neurons, and neuroinflammation. In this review, we summarize the recent literature on the involvement of autophagy in PD pathogenesis.

Autophagic mechanisms in longevity intervention: role of natural active compounds

The term 'autophagy' literally translates to 'self-eating' and alterations to autophagy have been identified as one of the several molecular changes that occur with aging in a variety of species. Autophagy and aging, have a complicated and multifaceted relationship that has recently come to light thanks to breakthroughs in our understanding of the various substrates of autophagy on tissue homoeostasis. Several studies have been conducted to reveal the relationship between autophagy and age-related diseases. The present review looks at a few new aspects of autophagy and speculates on how they might be connected to both aging and the onset and progression of disease. Additionally, we go over the most recent preclinical data supporting the use of autophagy modulators as age-related illnesses including cancer, cardiovascular and neurodegenerative diseases, and metabolic dysfunction. It is crucial to discover important targets in the autophagy pathway in order to create innovative therapies that effectively target autophagy. Natural products have pharmacological properties that can be therapeutically advantageous for the treatment of several diseases and they also serve as valuable sources of inspiration for the development of possible new small-molecule drugs. Indeed, recent scientific studies have shown that several natural products including alkaloids, terpenoids, steroids, and phenolics, have the ability to alter a number of important autophagic signalling pathways and exert therapeutic effects, thus, a wide range of potential targets in various stages of autophagy have been discovered. In this review, we summarised the naturally occurring active compounds that may control the autophagic signalling pathways.

Lysosomal Pathogenesis of Parkinson's Disease: Insights From LRRK2 and GBA1 Rodent Models

The discovery of mutations in LRRK2 and GBA1 that are linked to Parkinson's disease provided further evidence that autophagy and lysosome pathways are likely implicated in the pathogenic process. Their protein products are important regulators of lysosome function. LRRK2 has kinase-dependent effects on lysosome activity, autophagic efficacy and lysosomal Ca2+ signaling. Glucocerebrosidase (encoded by GBA1) is a hydrolytic enzyme contained in the lysosomes and contributes to the degradation of alpha-synuclein. PD-related mutations in LRRK2 and GBA1 slow the degradation of alpha-synuclein, thus directly implicating the dysfunction of the process in the neuropathology of Parkinson's disease. The development of genetic rodent models of LRRK2 and GBA1 provided hopes of obtaining reliable preclinical models in which to study pathogenic processes and perform drug validation studies. Here, I will review the extensive characterization of these models, their impact on understanding lysosome alterations in the course of Parkinson's disease and what novel insights have been obtained. In addition, I will discuss how these models fare with respect to the features of a "gold standard" animal models and what could be attempted in future studies to exploit LRRK2 and GBA1 rodent models in the fight against Parkinson's disease.

Intersection of the Orphan G Protein-Coupled Receptor, GPR19, with the Aging Process

G protein-coupled receptors (GPCRs) represent one of the most functionally diverse classes of transmembrane proteins. GPCRs and their associated signaling systems have been linked to nearly every physiological process. They also constitute nearly 40% of the current pharmacopeia as direct targets of remedial therapies. Hence, their place as a functional nexus in the interface between physiological and pathophysiological processes suggests that GPCRs may play a central role in the generation of nearly all types of human disease. Perhaps one mechanism through which GPCRs can mediate this pivotal function is through the control of the molecular aging process. It is now appreciated that, indeed, many human disorders/diseases are induced by GPCR signaling processes linked to pathological aging. Here we discuss one such novel member of the GPCR family, GPR19, that may represent an important new target for novel remedial strategies for the aging process. The molecular signaling pathways (metabolic control, circadian rhythm regulation and stress responsiveness) associated with this recently characterized receptor suggest an important role in aging-related disease etiology.

LRRK2 and Lipid Pathways: Implications for Parkinson's Disease

Genetic alterations in the LRRK2 gene, encoding leucine-rich repeat kinase 2, are a common risk factor for Parkinson's disease. How LRRK2 alterations lead to cell pathology is an area of ongoing investigation, however, multiple lines of evidence suggest a role for LRRK2 in lipid pathways. It is increasingly recognized that in addition to being energy reservoirs and structural entities, some lipids, including neural lipids, participate in signaling cascades. Early investigations revealed that LRRK2 localized to membranous and vesicular structures, suggesting an interaction of LRRK2 and lipids or lipid-associated proteins. LRRK2 substrates from the Rab GTPase family play a critical role in vesicle trafficking, lipid metabolism and lipid storage, all processes which rely on lipid dynamics. In addition, LRRK2 is associated with the phosphorylation and activity of enzymes that catabolize plasma membrane and lysosomal lipids. Furthermore, LRRK2 knockout studies have revealed that blood, brain and urine exhibit lipid level changes, including alterations to sterols, sphingolipids and phospholipids, respectively. In human LRRK2 mutation carriers, changes to sterols, sphingolipids, phospholipids, fatty acyls and glycerolipids are reported in multiple tissues. This review summarizes the evidence regarding associations between LRRK2 and lipids, and the functional consequences of LRRK2-associated lipid changes are discussed.

Molecular Pathways Involved in LRRK2-Linked Parkinson’s Disease: A Systematic Review

Parkinson’s disease is one of the most common neurodegenerative diseases affecting the ageing population, with a prevalence that has doubled over the last 30 years. As the mechanism of the disease is not fully elucidated, the current treatments are unable to effectively prevent neurodegeneration. Studies have found that mutations in Leucine-rich-repeat-kinase 2 (LRRK2) are the most common cause of familial Parkinson’s disease (PD). Moreover, aberrant (higher) LRRK2 kinase activity has an influence in idiopathic PD as well. Hence, the aim of this review is to categorize and synthesize current information related to LRRK2-linked PD and present the factors associated with LRRK2 that can be targeted therapeutically. A systematic review was conducted using the databases PubMed, Medline, SCOPUS, SAGE, and Cochrane (January 2016 to July 2021). Search terms included “Parkinson’s disease”, “mechanism”, “LRRK2”, and synonyms in various combinations. The search yielded a total of 988 abstracts for initial review, 80 of which met the inclusion criteria. Here, we emphasize molecular mechanisms revealed in recent in vivo and in vitro studies. By consolidating the recent updates in the field of LRRK2-linked PD, researchers can further evaluate targets for therapeutic application.

LRRK2 kinase activity regulates GCase level and enzymatic activity differently depending on cell type in Parkinson's disease

Leucine-rich repeat kinase 2 (LRRK2) is a kinase involved in different cellular functions, including autophagy, endolysosomal pathways, and immune function. Mutations in LRRK2 cause autosomal-dominant forms of Parkinson's disease (PD). Heterozygous mutations in GBA1, the gene encoding the lysosomal enzyme glucocerebrosidase (GCase), are the most common genetic risk factors for PD. Moreover, GCase function is altered in idiopathic PD and in other genetic forms of the disease. Recent work suggests that LRRK2 kinase activity can regulate GCase function. However, both a positive and a negative correlation have been described. To gain insights into the impact of LRRK2 on GCase, we performed a comprehensive analysis of GCase levels and activity in complementary LRRK2 models, including (i) LRRK2 G2019S knock in (GSKI) mice, (ii) peripheral blood mononuclear cell (PBMCs), plasma, and fibroblasts from PD patients carrying LRRK2 G2019S mutation, (iii) patient iPSCs-derived neurons; (iv) endogenous and overexpressed cell models. In some of these models we found a positive correlation between the activities of LRRK2 and GCase, which was further confirmed in cell lines with genetic and pharmacological manipulation of LRRK2 kinase activity. GCase protein level is reduced in GSKI brain tissues and in G2019S iPSCs-derived neurons, but increased in fibroblasts and PBMCs from patients, suggesting cell-type-specific effects. Overall, our study indicates that LRRK2 kinase activity affects both the levels and the catalytic activity of GCase in a cell-type-specific manner, with important implications in the context of therapeutic application of LRRK2 inhibitors in GBA1-linked and idiopathic PD.

Dopamine Transporter, PhosphoSerine129 α-Synuclein and α-Synuclein Levels in Aged LRRK2 G2019S Knock-In and Knock-Out Mice

The G2019S mutation in leucine rich-repeat kinase 2 (LRRK2) is a major cause of familial Parkinson’s disease. We previously reported that G2019S knock-in mice manifest dopamine transporter dysfunction and phosphoSerine129 α-synuclein (pSer129 α-syn) immunoreactivity elevation at 12 months of age, which might represent pathological events leading to neuronal degeneration. Here, the time-dependence of these changes was monitored in the striatum of 6, 9, 12, 18 and 23-month-old G2019S KI mice and wild-type controls using DA uptake assay, Western analysis and immunohistochemistry. Western analysis showed elevation of membrane dopamine transporter (DAT) levels at 9 and 12 months of age, along with a reduction of vesicular monoamine transporter 2 (VMAT2) levels at 12 months. DAT uptake was abnormally elevated from 9 to up to 18 months. DAT and VMAT2 level changes were specific to the G2019S mutation since they were not observed in LRRK2 kinase-dead or knock-out mice. Nonetheless, dysfunctional DAT uptake was not normalized by acute pharmacological inhibition of LRRK2 kinase activity with MLi-2. Immunoblot analysis showed elevation of pSer129 α-syn levels in the striatum of 12-month-old G2019S KI mice, which, however, was not confirmed by immunohistochemical analysis. Instead, total α-syn immunoreactivity was found elevated in the striatum of 23-month-old LRRK2 knock-out mice. These data indicate mild changes in DA transporters and α-syn metabolism in the striatum of 12-month-old G2019S KI mice whose pathological relevance remains to be established.

Modeling Parkinson's disease in LRRK2 mice: focus on synaptic dysfunction and the autophagy-lysosomal pathway

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are associated with familial and sporadic forms of Parkinson's disease (PD), for which the LRRK2 locus itself represents a risk factor. Idiopathic and LRRK2-related PD share the main clinical and neuropathological features, thus animals harboring the most common LRRK2 mutations, i.e. G2019S and R1441C/G, have been generated to replicate the parkinsonian phenotype and investigate the underlying pathological mechanisms. Most LRRK2 rodent models, however, fail to show the main neuropathological hallmarks of the disease i.e. the degeneration of dopaminergic neurons in the substantia nigra pars compacta and presence of Lewy bodies or Lewy body-like aggregates of α-synuclein, lacking face validity. Rather, they manifest dysregulation in cellular pathways and functions that confer susceptibility to a variety of parkinsonian toxins/triggers and model the presymptomatic/premotor stages of the disease. Among such susceptibility factors, dysregulation of synaptic activity and proteostasis are evident in LRRK2 mutants. These abnormalities are also manifest in the PD brain and represent key events in the development and progression of the pathology. The present minireview covers recent articles (2018-2021) investigating the role of LRRK2 and LRRK2 mutants in the regulation of synaptic activity and autophagy-lysosomal pathway. These articles confirm a perturbation of synaptic vesicle endocytosis and glutamate release in LRRK2 mutants. Likewise, LRRK2 mutants show a marked impairment of selective forms of autophagy (i.e. mitophagy and chaperone-mediated autophagy) and lysosomal function, with minimal perturbations of nonselective autophagy. Thus, LRRK2 rodents might help understand the contribution of these pathways to PD.

LRRK2 mutant knock-in mouse models: therapeutic relevance in Parkinson's disease

Mutations in the leucine-rich repeat kinase 2 gene (LRRK2) are one of the most frequent genetic causes of both familial and sporadic Parkinson’s disease (PD). Mounting evidence has demonstrated pathological similarities between LRRK2-associated PD (LRRK2-PD) and sporadic PD, suggesting that LRRK2 is a potential disease modulator and a therapeutic target in PD. LRRK2 mutant knock-in (KI) mouse models display subtle alterations in pathological aspects that mirror early-stage PD, including increased susceptibility of nigrostriatal neurotransmission, development of motor and non-motor symptoms, mitochondrial and autophagy-lysosomal defects and synucleinopathies. This review provides a rationale for the use of LRRK2 KI mice to investigate the LRRK2-mediated pathogenesis of PD and implications from current findings from different LRRK2 KI mouse models, and ultimately discusses the therapeutic potentials against LRRK2-associated pathologies in PD.

In vivo susceptibility to energy failure parkinsonism and LRRK2 kinase activity

The G2019S mutation of LRRK2 represents a risk factor for idiopathic Parkinson's disease. Here, we investigate whether LRRK2 kinase activity regulates susceptibility to the environmental toxin 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP). G2019S knock-in mice (bearing enhanced kinase activity) showed greater nigro-striatal degeneration compared to LRRK2 knock-out, LRRK2 kinase-dead and wild-type mice following subacute MPTP treatment. LRRK2 kinase inhibitors PF-06447475 and MLi-2, tested under preventive or therapeutic treatments, protected against nigral dopamine cell loss in G2019S knock-in mice. MLi-2 also rescued striatal dopaminergic terminal degeneration in both G2019S knock-in and wild-type mice. Immunoblot analysis of LRRK2 Serine935 phosphorylation levels confirmed target engagement of LRRK2 inhibitors. However, MLi-2 abolished phosphoSerine935 levels in the striatum and midbrain of both wild-type and G2019S knock-in mice whereas PF-06447475 partly reduced phosphoSerine935 levels in the midbrain of both genotypes. In vivo and ex vivo uptake of the 18-kDa translocator protein (TSPO) ligand [¹⁸F]-VC701 revealed a similar TSPO binding in MPTP-treated wild-type and G2019S knock-in mice which was consistent with an increased GFAP striatal expression as revealed by Real Time PCR. We conclude that LRRK2 G2019S, likely through enhanced kinase activity, confers greater susceptibility to mitochondrial toxin-induced parkinsonism. LRRK2 kinase inhibitors are neuroprotective in this model.

Glucocerebrosidase 1 and leucine-rich repeat kinase 2 in Parkinson disease and interplay between the two genes

The glucocerebrosidase 1 gene (GBA1), bi-allelic variants of which cause Gaucher disease (GD), encodes the lysosomal enzyme glucocerebrosidase (GCase) and is a risk factor for Parkinson Disease (PD). GBA1 variants are linked to a reduction in GCase activity in the brain. Variants in Leucine-Rich Repeat Kinase 2 (LRRK2), such as the gain-of-kinase-function variant G2019S, cause the most common familial form of PD. In patients without GBA1 and LRRK2 mutations, GCase and LRRK2 activity are also altered, suggesting that these two genes are implicated in all forms of PD and that they may play a broader role in PD pathogenesis. In this review, we review the proposed roles of GBA1 and LRRK2 in PD, focussing on the endolysosomal pathway. In particular, we highlight the discovery of Ras-related in brain (Rab) guanosine triphosphatases (GTPases) as LRRK2 kinase substrates and explore the links between increased LRRK2 activity and Rab protein function, lysosomal dysfunction, alpha-synuclein accumulation and GCase activity. We also discuss the discovery of RAB10 as a potential mediator of LRRK2 and GBA1 interaction in PD. Finally, we discuss the therapeutic implications of these findings, including current approaches and future perspectives related to novel drugs targeting LRRK2 and GBA1.