Loss of leucine-rich repeat kinase 2 causes impairment of protein degradation pathways, accumulation of α-synuclein, and apoptotic cell death in aged mice

Abstract

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common genetic cause of Parkinson's disease. LRRK2 is a large protein containing a small GTPase domain and a kinase domain, but its physiological role is unknown. To identify the normal function of LRRK2 in vivo, we generated two independent lines of germ-line deletion mice. The dopaminergic system of LRRK2 −/− mice appears normal, and numbers of dopaminergic neurons and levels of striatal dopamine are unchanged. However, LRRK2 −/− kidneys, which suffer the greatest loss of LRRK compared with other organs, develop striking accumulation and aggregation of α-synuclein and ubiquitinated proteins at 20 months of age. The autophagy-lysosomal pathway is also impaired in the absence of LRRK2, as indicated by accumulation of lipofuscin granules as well as altered levels of LC3-II and p62. Furthermore, loss of LRRK2 dramatically increases apoptotic cell death, inflammatory responses, and oxidative damage. Collectively, our findings show that LRRK2 plays an essential and unexpected role in the regulation of protein homeostasis during aging, and suggest that LRRK2 mutations may cause Parkinson's disease and cell death via impairment of protein degradation pathways, leading to α-synuclein accumulation and aggregation over time.Parkinson's disease | knockout | autophagy | ubiquitin-proteasome system | aging P arkinson's disease (PD) is the most common movement disorder. The neuropathological hallmarks of PD are progressive degeneration of dopaminergic (DA) neurons and the presence of intraneuronal cytoplasmic inclusions known as Lewy bodies, of which α-synuclein is a major constituent (1). Dominantly inherited mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of familial PD (2, 3), highlighting the importance of LRRK2 in PD pathogenesis; however, the normal physiological role of LRRK2 is unknown. LRRK2 is a large protein containing a Ras-like small GTPase domain and a MAPKKK-like kinase domain, and has a functional homolog LRRK1, which shares similar domain structures (4). Crystal structural and biochemical studies showed that the GTPase domain forms a dimer; the pathogenic mutations destabilize the dimer and reduce GTPase activity (5-7). A recent in vitro study suggested that LRRK2 and LRRK1 can interact with each other and form a heterodimer (8). Although no physiological substrate of the LRRK2 kinase activity has been reported, studies in cultured cells have suggested that some pathogenic mutations in LRRK2 cause increases in LRRK2 kinase activity (9, 10).Protein aggregation is thought to play a major role in neurodegeneration and PD pathogenesis (11). The strongest evidence came from studies of α-synuclein. Gene multiplication and missense mutations in α-synuclein have been identified in early-onset familial PD with dominant inheritance (12). α-Synuclein is a major constituent of Lewy bodies (1). Overexpression of either WT or mutant α-synuclein in transgenic mice causes age-related neurodegeneration (13-15). Although patients carryi...

Age-related changes in the function of autophagy in rat kidneys

“…It has been postulated that those dysfunctional mitochondria may undergo further oxidative damage, resulting in increased ROS production and decreased energy production (Terman et al 2003). These results suggest that deficiency in autophagy leads to an accumulation of damaged mitochondria (Wohlgemuth et al 2007;Kume et al 2010;Tong et al 2010). There is growing evidence that the efficiency of the degradative system involved in mitochondrial turnover declines with age.…”

Revisiting oxidative stress and mitochondrial dysfunction in the pathogenesis of Parkinson disease—resemblance to the effect of amphetamine drugs of abuse

“…Particularly, most patients with the G2019S mutation exhibitedalphaͲsynͲpositive LBs as in sporadic PD [206,208,209]. Tong et al(2010) [210], showed that accumulation and aggregation of alphaͲsyn and ubiquitinated proteins occurred in aged LRRK2 germͲline deletion mice with great loss of LRRK2. The autophagyͲlysosomal pathway was impaired together with an increase in apoptotic cell death, inflammatory response and oxidative stress.…”

Role of Endoplasmic Reticulum Stress and Unfolded Protein Responses in Health and Diseases

“…These reports suggest that UPR mediates shift of the balance towards apoptosis [119]. Moreover, mutations in leucine-rich repeat kinase 2 (LRRK2), also an autosomal dominant PD gene, causes impairment in protein degradation pathways, accumulation of oxidized proteins, impairment of the autophagy-lysosomal pathway, accumulation of a-synuclein and ubiquitinated proteins [120]. LRRK2 has been observed to localize in core of Lewy bodies [121] and is known to upregulate GRP78, a key cell survival molecule during ER stress [122].…”