Parkinson’s disease (PD) is characterized by dopaminergic neuronal loss in the substantia nigra pars compacta and intracellular inclusions called Lewy bodies (LB). During the course of disease, misfolded α-synuclein, the major constituent of LB, spreads to different regions of the brain in a prion-like fashion, giving rise to successive non-motor and motor symptoms. Etiology is likely multifactorial, and involves interplay among aging, genetic susceptibility and environmental factors. The prevalence of PD rises exponentially with age, and aging is associated with impairment of cellular pathways which increases susceptibility of dopaminergic neurons to cell death. However, the majority of those over the age of 80 do not have PD, thus other factors in addition to aging are needed to cause disease. Discovery of neurotoxins which can result in parkinsonism led to efforts in identifying environmental factors which may influence PD risk. Nevertheless, the causality of most environmental factors is not conclusively established, and alternative explanations such as reverse causality and recall bias cannot be excluded. The lack of geographic clusters and conjugal cases also go against environmental toxins as a major cause of PD. Rare mutations as well as common variants in genes such as SNCA, LRRK2 and GBA are associated with risk of PD, but Mendelian causes collectively only account for 5% of PD and common polymorphisms are associated with small increase in PD risk. Heritability of PD has been estimated to be around 30%. Thus, aging, genetics and environmental factors each alone is rarely sufficient to cause PD for most patients. PD is a multifactorial disorder involving interplay of aging, genetics and environmental factors. This has implications on the development of appropriate animal models of PD which take all these factors into account. Common converging pathways likely include mitochondrial dysfunction, impaired autophagy, oxidative stress and neuroinflammation, which are associated with the accumulation and spread of misfolded α-synuclein and neurodegeneration. Understanding the mechanisms involved in the initiation and progression of PD may lead to potential therapeutic targets to prevent PD or modify its course.

Parkinson disease (PD) is an age-related neurodegenerative disorder associated with misfolded SNCA/α-synuclein accumulation in brain. Impaired catabolism of SNCA potentiates formation of its toxic oligomers. LRRK2 (leucine-rich repeat kinase-2) mutations predispose to familial and sporadic PD. Mutant LRRK2 perturbs chaperone-mediated-autophagy (CMA) to degrade SNCA. We showed greater age-dependent accumulation of oligomeric SNCA in striatum and cortex of aged LRRK2^R1441G knockin (KI) mice, compared to age-matched wildtype (WT) by 53% and 31%, respectively. Lysosomal clustering and accumulation of CMA-specific LAMP2A and HSPA8/HSC70 proteins were observed in aged mutant striatum along with increased GAPDH (CMA substrate) by immunohistochemistry of dorsal striatum and flow cytometry of ventral midbrain cells. Using our new reporter protein clearance assay, mutant mouse embryonic fibroblasts (MEFs) expressing either SNCA or CMA recognition ‘KFERQ’-like motif conjugated with photoactivated-PAmCherry showed slower cellular clearance compared to WT by 28% and 34%, respectively. However, such difference was not observed after the ‘KFERQ’-motif was mutated. LRRK2 mutant MEFs exhibited lower lysosomal degradation than WT indicating lysosomal dysfunction. LAMP2A-knockdown reduced total lysosomal activity and clearance of ‘KFERQ’-substrate in WT but not in mutant MEFs, indicating impaired CMA in the latter. A CMA-specific activator, AR7, induced neuronal LAMP2A transcription and lysosomal activity in MEFs. AR7 also attenuated the progressive accumulation of both intracellular and extracellular SNCA oligomers in prolonged cultures of mutant cortical neurons (DIV21), indicating that oligomer accumulation can be suppressed by CMA activation. Activation of autophagic pathways to reduce aged-related accumulation of pathogenic SNCA oligomers is a viable disease-modifying therapeutic strategy for PD. Abbreviations: 3-MA: 3-methyladenine; AR7: 7-chloro-3-(4-methylphenyl)-2H-1,4-benzoxazine; CMA: chaperone-mediated autophagy; CQ: chloroquine; CSF: cerebrospinal fluid; DDM: n-dodecyl β-D-maltoside; DIV: days in vitro; ELISA: enzyme-linked immunosorbent assay; FACS: fluorescence-activated cell sorting; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GWAS: genome-wide association studies; HSPA8/HSC70: heat shock protein 8; KFERQ: CMA recognition pentapeptide; KI: knockin; LAMP1: lysosomal-associated membrane protein 1; LAMP2A: lysosomal-associated membrane protein 2A; LDH: lactate dehydrogenase; LRRK2: leucine-rich repeat kinase 2; MEF: mouse embryonic fibroblast; NDUFS4: NADH:ubiquinone oxidoreductase core subunit S4; NE: novel epitope; PD: Parkinson disease; RARA/RARα: retinoic acid receptor, alpha; SNCA: synuclein, alpha; TUBB3/TUJ1: tubulin, beta 3 class III; WT: wild-type

Background: Visual hallucinations (VH) are one of the most striking nonmotor symptoms in Parkinson's disease (PD), and predict dementia and mortality. Aberrant default mode network (DMN) is associated with other psychoses. Here, we tested the hypothesis that DMN dysfunction contributes to VH in PD. Methods: Resting state functional data was acquired from individuals with PD with VH (PDVH) and without VH (PDnonVH), matched for levodopa drug equivalent dose, and a healthy control group (HC). Independent component analysis was used to investigate group differences in functional connectivity within the DMN. In addition, we investigated whether the functional changes associated with hallucinations were accompanied by differences in cortical thickness. Results: There were no group differences in cortical thickness but functional coactivation within components of the DMN was significantly lower in both PDVH and PDnonVH groups compared to HC. Functional coactivation within the DMN was found to be greater in PDVH group relative to PDnonVH group. Conclusion: Our study demonstrates, for the first time that, within a functionally abnormal DMN in PD, relatively higher “connectivity” is associated with VH. We postulate that aberrant connectivity in a large scale network affects sensory information processing and perception, and contributes to “positive” symptom generation in PD. Hum Brain Mapp 35:5658–5666, 2014. © 2014 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.

Uncoupling proteins (UCPs) belong to a large family of mitochondrial solute carriers 25 (SLC25s) localized at the inner mitochondrial membrane. UCPs transport protons directly from the intermembrane space to the matrix. Of five structural homologues (UCP1 to 5), UCP4 and 5 are principally expressed in the central nervous system (CNS). Neurons derived their energy in the form of ATP that is generated through oxidative phosphorylation carried out by five multiprotein complexes (Complexes I–V) embedded in the inner mitochondrial membrane. In oxidative phosphorylation, the flow of electrons generated by the oxidation of substrates through the electron transport chain to molecular oxygen at Complex IV leads to the transport of protons from the matrix to the intermembrane space by Complex I, III, and IV. This movement of protons to the intermembrane space generates a proton gradient (mitochondrial membrane potential; MMP) across the inner membrane. Complex V (ATP synthase) uses this MMP to drive the conversion of ADP to ATP. Some electrons escape to oxygen‐forming harmful reactive oxygen species (ROS). Proton leakage back to the matrix which bypasses Complex V resulting in a major reduction in ROS formation while having a minimal effect on MMP and hence, ATP synthesis; a process termed “mild uncoupling.” UCPs act to promote this proton leakage as means to prevent excessive build up of MMP and ROS formation. In this review, we discuss the structure and function of mitochondrial UCPs 4 and 5 and factors influencing their expression. Hypotheses concerning the evolution of the two proteins are examined. The protective mechanisms of the two proteins against neurotoxins and their possible role in regulating intracellular calcium movement, particularly with regard to the pathogenesis of Parkinson's disease are discussed.

Mitochondrial dysfunction causes energy deficiency and nigrostriatal neurodegeneration which is integral to the pathogenesis of Parkinson disease (PD). Clearance of defective mitochondria involves fission and ubiquitin-dependent degradation via mitophagy to maintain energy homeostasis. We hypothesize that LRRK2 (leucine-rich repeat kinase 2) mutation disrupts mitochondrial turnover causing accumulation of defective mitochondria in aging brain. We found more ubiquitinated mitochondria with aberrant morphology associated with impaired function in aged (but not young) LRRK2^R1441G knockin mutant mouse striatum compared to wild-type (WT) controls. LRRK2^R1441G mutant mouse embryonic fibroblasts (MEFs) exhibited reduced MAP1LC3/LC3 activation indicating impaired macroautophagy/autophagy. Mutant MEFs under FCCP-induced (mitochondrial uncoupler) stress showed increased LC3-aggregates demonstrating impaired mitophagy. Using a novel flow cytometry assay to quantify mitophagic rates in MEFs expressing photoactivatable mito-PAmCherry, we found significantly slower mitochondria clearance in mutant cells. Specific LRRK2 kinase inhibition using GNE-7915 did not alleviate impaired mitochondrial clearance suggesting a lack of direct relationship to increased kinase activity alone. DNM1L/Drp1 knockdown in MEFs slowed mitochondrial clearance indicating that DNM1L is a prerequisite for mitophagy. DNM1L knockdown in slowing mitochondrial clearance was less pronounced in mutant MEFs, indicating preexisting impaired DNM1L activation. DNM1L knockdown disrupted mitochondrial network which was more evident in mutant MEFs. DNM1L-Ser616 and MAPK/ERK phosphorylation which mediate mitochondrial fission and downstream mitophagic processes was apparent in WT using FCCP-induced stress but not mutant MEFs, despite similar total MAPK/ERK and DNM1L levels. In conclusion, aberrant mitochondria morphology and dysfunction associated with impaired mitophagy and DNM1L-MAPK/ERK signaling are found in mutant LRRK2 MEFs and mouse brain. Abbreviations: ATP: adenosine triphosphate; BAX: BCL2-associated X protein; CDK1: cyclin-dependent kinase 1; CDK5: cyclin-dependent kinase 5; CQ: chloroquine; CSF: cerebrospinal fluid; DNM1L/DRP1: dynamin 1-like; ELISA: enzyme-linked immunosorbent assay; FACS: fluorescence-activated cell sorting; FCCP: carbonyl cyanide-4-(trifluoromethoxy)phenylhydrazone; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; LAMP2A: lysosomal-associated membrane protein 2A; LRRK2: leucine-rich repeat kinase 2; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MAPK1/ERK2: mitogen-activated protein kinase 1; MEF: mouse embryonic fibroblast; MFN1: mitofusin 1; MMP: mitochondrial membrane potential; PAmCherry: photoactivatable-mCherry; PD: Parkinson disease; PINK1: PTEN induced putative kinase 1; PRKN/PARKIN: parkin RBR E3 ubiquitin protein ligase; RAB10: RAB10, member RAS oncogene family; RAF: v-raf-leukemia oncogene; SNCA: synuclein, alpha; TEM: transmission electron microscopy; VDAC: voltage-dependent anion channel; WT: wild type; SQSTM1/p62: sequestosome 1.

Background: Major intracerebral hemorrhage (ICH) trials have largely been unable to demonstrate therapeutic benefit in improving functional outcomes. This may be partly due to the heterogeneity of ICH outcomes based on their location, where a small strategic ICH could be debilitating, thus confounding therapeutic effects. We aimed to determine the ideal hematoma volume cutoff for different ICH locations in predicting ICH outcomes. Methods: We retrospectively analyzed consecutive ICH patients enrolled in the University of Hong Kong prospective stroke registry from January 2011 to December 2018. Patients with premorbid modified Rankin Scale score >2 or who underwent neurosurgical intervention were excluded. ICH volume cutoff, sensitivity, and specificity in predicting respective 6-month neurological outcomes (good [modified Rankin Scale score 0–2], poor [modified Rankin Scale score 4–6], and mortality) for specific ICH locations were determined using receiver operating characteristic curves. Separate multivariate logistic regression models were also conducted for each location-specific volume cutoff to determine whether these cutoffs were independently associated with respective outcomes. Results: Among 533 ICHs, the volume cutoff for good outcome according to ICH location was 40.5 mL for lobar, 32.5 mL for putamen/external capsule, 5.5 mL for internal capsule/globus pallidus, 6.5 mL for thalamus, 17 mL for cerebellum, and 3 mL for brainstem. ICH smaller than the cutoff for all supratentorial sites had higher odds of good outcomes (all P <0.05). Volumes exceeding 48 mL for lobar, 41 mL for putamen/external capsule, 6 mL for internal capsule/globus pallidus, 9.5 mL for thalamus, 22 mL for cerebellum, and 7.5 mL for brainstem were at greater risk of poor outcomes (all P <0.05). Mortality risks were significantly higher for volumes that exceeded 89.5 mL for lobar, 42 mL for putamen/external capsule, and 21 mL for internal capsule/globus pallidus (all P 0.8), except in predicting good outcome for cerebellum. Conclusions: ICH outcomes differed with location-specific hematoma size. Location-specific volume cutoff should be considered in patient selection for ICH trials.