Aberrant mitochondrial morphology and function associated with impaired mitophagy and DNM1L-MAPK/ERK signaling are found in aged mutant Parkinsonian LRRK2^R1441Gmice

Abstract

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 ubiquitindependent degradation via mitophagy to maintain energy homeostasis. We hypothesize that LRRK2 (leucinerich 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.

Protective Effect of Optic Atrophy 1 on Cardiomyocyte Oxidative Stress: Roles of Mitophagy, Mitochondrial Fission, and MAPK/ERK Signaling

“…Finally, we also report that Opa1-mediated mitophagy is an upstream trigger of the MAPK/ERK pathway in cardiomyocytes. This is in line with previous studies, conducted in aged parkinsonian mice [71][72][73], in a murine model of sleep apnea [74], and in a model of doxorubicin-induced cardiotoxicity [75] that highlighted the relationship between mitophagy and the ERK signaling pathway. Considering the necessary role played by ERK in regulating cardiomyocyte metabolism and ATP generation, mitophagy-induced ERK activation appears as a critical mechanism to support mitochondrial metabolism and oxidative phosphorylation under hypoxic conditions.…”

LRRK2, GBA and their interaction in the regulation of autophagy: implications on therapeutics in Parkinson's disease

“…Impairment of lysosomal function causes broad abnormalities in autophagy that ultimately lead to accumulation of toxic oligomeric α-syn, which further impairs autophagy, forming a vicious cycle. Mitochondrial dysfunction and impaired mitophagy have also been described in LRRK2 and GBA mutations, which are likely linked to reduced efficiency of ALP [ 119 , 120 ]. Specifically, in a mouse model with heterozygous GBA L444P mutation and another mouse model with LRRK2 R1441C homozygous knockin mutation, accumulation of mitochondria with abnormal morphology, increased oxidative stress, reduced ATP production, increased accumulation of autophagosomes with reduced rate of mitophagy has been described [ 119 , 120 ].…”

“…Mitochondrial dysfunction and impaired mitophagy have also been described in LRRK2 and GBA mutations, which are likely linked to reduced efficiency of ALP [ 119 , 120 ]. Specifically, in a mouse model with heterozygous GBA L444P mutation and another mouse model with LRRK2 R1441C homozygous knockin mutation, accumulation of mitochondria with abnormal morphology, increased oxidative stress, reduced ATP production, increased accumulation of autophagosomes with reduced rate of mitophagy has been described [ 119 , 120 ]. These abnormalities are consistent with mitochondrial dysfunction observed in PD, with impaired electron transport chain function, impaired calcium buffering and abnormal mitochondrial morphology and dynamics (reviewed in [ 121 , 122 ]).…”

A Conserved Role for LRRK2 and Roco Proteins in the Regulation of Mitochondrial Activity

“…Impaired mitochondrial activity is a common characteristic of both, iPD and familial PD, and several genes linked to PD play an important role in mitochondrial quality control ( Narendra et al, 2008 ; Youle and van der Bliek, 2012 ; Liu et al, 2017 ; Toyofuku et al, 2019 ; Delcambre et al, 2020 ; Weindel et al, 2020 ). Even though the mitochondrial morphology was found to be affected e.g., in age mutant Parkinsonian LRRK2(R1441G) mice, mitochondrial shape does not qualify as a biomarker as it is mainly detected in late stages of PD and/or post mortem and inconsistent with the disease pattern ( Liu et al, 2020 ). One theory regarding the underlying trigger of PD involves the presence and accumulation of oxidative stress.…”