Novel Role of PINK1 in Mitochondrial Function

Abstract

Phosphatase and tensin homolog (PTEN) induced kinase 1 (PINK1), linked to familial Parkinson’s disease (PD), is known to affect mitochondrial homeostasis. Mutations in PINK1 result in the decreased enzyme activity of mitochondrial electron transport chain (ETC) and the disrupted mitochondrial dynamics. Parkin, another protein associated with familial PD, could partially rescue altered mitochondria morphology and cell death caused by PINK1 mutations. However, the precise role of PINK1 in the regulation of mitochondrial ETC enzyme and rescue mechanism of parkin remains unknown. In this study, it was demonstrated that: (i) the novel regulatory role of PINK1 in ETC complex IV activity, (ii) the recovery action of optimal nitric oxide (NO) signaling from complex IV deficit in PINK1 null condition, and (iii) the protective mechanism of parkin in PINK1-deficient pathological condition. In PINK1 null cells, the levels of specific chaperones including Hsp60, LRPPRC, and Hsp90, were severely decreased. LRPPRC and Hsp90 were found to regulate complex IV activity at the upstream of Hsp60. Specifically, Hsp60 KD decreased in complex IV activity, while inhibition of Hsp90 by 17-AAG decreased both Hsp60 and complex IV activity. In contrast, overexpression of the PINK1-interacting factor, LRPPRC, augmented complex IV activity by upregulating Hsp60. A similar recovery of complex IV activity was also induced by coexpression of Hsp90 and Hsp60. Of interest, complex IV deficit could be substantially restored by treatment with NO at optimized of concentration, which resulted in upregulation of Hsp60, Hsp90 and LRPPRC in PINK1 null dopaminergic neurons. These results suggest that PINK1 regulates complex IV activity via interactions with upstream regulators of Hsp60, such as LRPPRC and Hsp90. Furthermore, treatment with SNP at optimized of concentration enhances functioning of the defective PINK1-Hsp90/LRPPRC-Hsp60-complex IV signaling axis in PINK1 null neurons by restoring proper NO signaling. Moreover, the PINK1 deficiency resulted in disruption of actin dynamics and increased recruitment of parkin to damaged actin filament. The same phenomena have also been induced by PD-related pathological conditions, such as oxidative stress and mitochondrial inhibition, suggesting that disrupted actin dynamics and increased interactions between actin filament and parkin may be a common mechanism in PD-related pathological condition. Taken together, these results suggest that increased interaction between parkin and actin may exert protective function against the damage associated with actin aggregates. Therefore, I propose that PINK1 regulates mitochondrial complex IV activity by its regulatory interaction with Hsp90 and LRPPRC and the defective PINK1-LRPPRC/Hsp90-Hsp60-complex IV signaling axis in PINK1 null neuronal cells can be rescued by restoration of optimal NO signaling. I speculate that actin aggregation accumulated in PINK1-deficient condition may be rescued by the increased interaction between parkin and actin. ;파킨슨씨병의 병리학적 특징은 중뇌 흑질에 분포하는 도파민 신경세포의 선택적 사멸과 미토콘드리아 기능이상 및 비 정상적 단백질 aggregates 관찰이 있다. PINK1은 미토콘드리아에 존재하며 돌연변이 시 유전성 파킨슨씨병을 유발하므로, PINK1의 기능 연구는 파킨슨씨병 치료 기전 연구에 도움을 줄 수 있다. 우리는 최초로 PINK1 결손 도파민 신경세포를 확립하였고, PINK1 결손에 의하여 미토콘드리아 complex IV 활성이 정상에 비하여 50% 감소된 것을 관찰했다. PINK1은 Hsp90, LRPPRC 그리고 Hsp60과 상호작용하며, LRPPRC와 Hsp90은 complex IV 활성 조절 시 Hsp60의 상위 단계에서 작용한다. Hsp90의 기능저해는 미토콘드리아의 Hsp60 발현 및 complex IV 활성감소를 야기하고, 과 발현된 Hsp90에 의하여 미토콘드리아 발현이 증가된 Hsp60은 PINK1 결손에 의하여 감소된 complex IV 활성을 회복시켰다. 또한 COXI mRNA 전사를 조절하는 LRPPRC도 PINK1 결손 도파민 신경세포에서 complex IV 활성을 개선하는데, 이 과정에서 Hsp60 발현 증가가 필수적인 요소 임을 알 수 있었다. 더불어 세포 내 NO 농도가 LRPPRC, Hsp90 그리고 Hsp60 발현 및 complex IV 활성에 영향을 주고, PINK1 결손 시 NO donor 인 SNP 처리가 complex IV 활성 회복에 기여하므로 PINK1 결손은 NO 신호전달의 장애를 유발하는 것으로 추정할 수 있다. 뿐만 아니라, PINK1 결손 시 나타나는 oxidative stress와 미토콘드리아 기능이상이 actin aggregate을 형성하며, E3 ligase인 parkin과 손상된 actin의 상호작용이 증가 하는 것을 관찰했다. 우리는 PINK1이 complex IV 활성의 조절인자 이며, PINK1과 NO 신호전달을 통한 미토콘드리아 전자전달계 조절 기전이 파킨슨씨병 치료 방법으로 활용될 가능성을 제시한다. 또한, parkin과 손상된 actin의 상호작용 증가는 actin aggregates의 제거 과정이며, 단백질의 정상적인 기능을 저해하는 aggregates의 생성 억제 및 제거 활성화 기전이 파킨슨씨병 치료에 응용 될 수 있음을 제안한다.