FUNDC1 collaborates with PINK1 in regulating mitochondrial Fission and compensating for PINK1 deficiency

PINK1 deficiency alleviates bleomycin-induced pulmonary fibrosis in mice

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive lung disorder marked by deteriorating dyspnea and declining pulmonary function. Despite its rising prevalence and incidence, therapeutic options remain limited. PTEN-induced kinase 1 (PINK1), known for its role in PINK1/Parkin-dependent mitophagy, contributes to the pathogenesis of various lung diseases. In this study, we elucidate a previously unrecognized mechanism of PINK1, beyond its canonical mitophagy function, during pulmonary fibrosis. We established a bleomycin (BLM)-induced pulmonary fibrosis model in Pink1 knockout (Pink1-/-) mice and treated BEAS-2B cells with transforming growth factor-beta 1 (TGF-β1) to simulate the microenvironment of pulmonary fibrosis. A significant elevation in PINK1 expression was observed in vivo and in vitro systems. While PINK1/Parkin-dependent mitophagy was activated, mitophagy mediated by BCL2-interacting protein 3 (BNIP3) and FUN14 domain-containing 1 (FUNDC1) was suppressed. Further experiments in carbonyl cyanide m-chlorophenyl hydrazone (CCCP)-treated PINK1 knockout (KO) HEK293 cells and YFP-Parkin-expressing HeLa cells demonstrated that PINK1 deficiency enhanced BNIP3- and FUNDC1-mediated mitophagy, whereas PINK1 overexpression inhibited it. Moreover, dual BNIP3/FUNDC1 knockdown significantly reversed the anti-apoptotic effect of PINK1 KO. We conclude that PINK1 deficiency promotes the clearance of damaged mitochondria via BNIP3/FUNDC1 upregulation, preserving mitochondrial homeostasis, mitigating alveolar epithelial injury, and attenuating fibrosis. Thus, PINK1 may inhibit BNIP3- and FUNDC1-mediated mitophagy besides driving PINK1-dependent mitophagy during pulmonary fibrosis.

Mitophagy in Neurons: Mechanisms Regulating Mitochondrial Turnover and Neuronal Homeostasis

Mitochondrial quality control is instrumental in regulating neuronal health and survival. The receptor-mediated clearance of damaged mitochondria by autophagy, known as mitophagy, plays a key role in controlling mitochondrial homeostasis. Mutations in genes that regulate mitophagy are causative for familial forms of neurological disorders including Parkinson's disease (PD) and Amyotrophic lateral sclerosis (ALS). PINK1/Parkin-dependent mitophagy is the best studied mitophagy pathway, while more recent work has brought to light additional mitochondrial quality control mechanisms that operate either in parallel to or independent of PINK1/Parkin mitophagy. Here, we discuss our current understanding of mitophagy mechanisms operating in neurons to govern mitochondrial homeostasis. We also summarize progress in our understanding of the links between mitophagic dysfunction and neurodegeneration, and highlight the potential for therapeutic interventions to maintain mitochondrial health and neuronal function.

PRKN-linked familial Parkinson's disease: cellular and molecular mechanisms of disease-linked variants

Parkinson's disease (PD) is a common and incurable neurodegenerative disorder that arises from the loss of dopaminergic neurons in the substantia nigra and is mainly characterized by progressive loss of motor function. Monogenic familial PD is associated with highly penetrant variants in specific genes, notably the PRKN gene, where homozygous or compound heterozygous loss-of-function variants predominate. PRKN encodes Parkin, an E3 ubiquitin-protein ligase important for protein ubiquitination and mitophagy of damaged mitochondria. Accordingly, Parkin plays a central role in mitochondrial quality control but is itself also subject to a strict protein quality control system that rapidly eliminates certain disease-linked Parkin variants. Here, we summarize the cellular and molecular functions of Parkin, highlighting the various mechanisms by which PRKN gene variants result in loss-of-function. We emphasize the importance of high-throughput assays and computational tools for the clinical classification of PRKN gene variants and how detailed insights into the pathogenic mechanisms of PRKN gene variants may impact the development of personalized therapeutics.

Is There a Place for Lewy Bodies before and beyond Alpha-Synuclein Accumulation? Provocative Issues in Need of Solid Explanations

In the last two decades, alpha-synuclein (alpha-syn) assumed a prominent role as a major component and seeding structure of Lewy bodies (LBs). This concept is driving ongoing research on the pathophysiology of Parkinson's disease (PD). In line with this, alpha-syn is considered to be the guilty protein in the disease process, and it may be targeted through precision medicine to modify disease progression. Therefore, designing specific tools to block the aggregation and spreading of alpha-syn represents a major effort in the development of disease-modifying therapies in PD. The present article analyzes concrete evidence about the significance of alpha-syn within LBs. In this effort, some dogmas are challenged. This concerns the question of whether alpha-syn is more abundant compared with other proteins within LBs. Again, the occurrence of alpha-syn compared with non-protein constituents is scrutinized. Finally, the prominent role of alpha-syn in seeding LBs as the guilty structure causing PD is questioned. These revisited concepts may be helpful in the process of validating which proteins, organelles, and pathways are likely to be involved in the damage to meso-striatal dopamine neurons and other brain regions involved in PD.