p38 MAPK-DRP1 signaling is involved in mitochondrial dysfunction and cell death in mutant A53T α-synuclein model of Parkinson's disease

Highlights

• p38MAPK directly interacts with and phosphorylates the DRP1 at serine 616 site.

• p38MAPK activation leads to mitochondrial dysfunction and dopaminergic neuron death by disrupting mitochondrial homeostasis.

• p38MAPK-DRP1 signal pathway may be a viable therapeutic target of PD via maintenance of mitochondrial homeostasis.

Abstract

Abnormal accumulation of α-synuclein and mitochondria dynamics dysfunction are considered to be implicated in the pathogenesis of Parkinson's disease. However, the underlying mechanisms how α-synuclein abnormal accumulation causes mitochondrial dynamics dysfunction remains unclear. Here, we demonstrate that dynamin-related protein 1(DRP1) is a substrate for p38 MAPK, mutant α-synuclein overexpression in SN4741 cell caused p38 MAPK activation, p38 MAPK-mediated phosphorylation DRP1 at serine 616 to activate DRP1 and is associated with increased mitochondrial fission, which resulted in mitochondrial dysfunction and neuronal loss. Inhibition of p38 MAPK or expression of a kinase death form of p38 MAPK not only attenuates DRP1-mediated mitochondrial fission，but also restores the mitochondrial dysfunction and cell death in α-synuclein A53T model. These findings showed that inhibition of p38 MAPK-DRP1 signaling pathway may be a viable therapeutic strategy of PD on maintenance of mitochondrial homeostasis.

Introduction

Parkinson's disease is a common neurodegenerative disease characterized by degenerative death of midbrain substantia nigra dopaminergic neurons. The typical characteristics of Parkinsonian motor symptoms include bradykinesia, muscular rigidity, rest tremor and postural instability (Burbulla et al., 2017). Published researches have shown that α-synuclein aggregation and mitochondrial dysfunction are the main causes of neuronal degeneration in PD (Vicario et al., 2018; Zhao et al., 2019). α-synuclein toxicity leads to cell dysfunction through impairing synaptic function, defective mitochondrial and endoplasmic reticulum (ER) function as well as the autophagy-lysosomal pathway dysfunction (Grünewald et al., 2019). Although α-synuclein toxicity has been extensively investigated in PD, its regulatory networks on mitochondrial dysfunction, especially mitochondrial dynamics, is unclear.

Mitochondrial dynamics is regulated by fission and fusion, which are necessary for cell survival and cell growth. Mitochondrial fission facilitates the segregation of damaged mitochondria from a healthy network and mitochondrial transport through neuronal processes (Franco-Iborra et al., 2018). However, published evidence supports that excessive fission leads to mitochondrial and cellular dysfunction (Elgass et al., 2013). Mitochondrial fission is mediated by dynamin-related protein (DRP1), which is a large guanosine triphosphatases (GTPase). DRP1 is recruited from the cytosol to the mitochondria outer membrane that induces mitochondrial fragmentation (Wang et al., 2016). It has been reported that DRP1 activity is tightly regulated by posttranslational modifications, including phosphorylation, ubiquitination, SUMOylating, S-nitrosylation and so on (Tsushima et al., 2018). Multiple kinases regulate DRP1 phosphorylation at various sites, which disrupt mitochondrial homeostasis and result in cell death. Phosphorylation of DRP1 at Ser-637 by AKAP1 or AMPK plays critical protective roles through decreasing mitochondrial fission in the neural system(Wikstrom et al., 2013; Tsushima et al., 2018). However, phosphorylation of DRP1 at Ser-616 by ERK or at Tyr-266 by c-Abl promotes mitochondrial fission, which causes damage to the nervous system (Gan et al., 2014; Zhou et al., 2017). Ca²⁺/Calmodulin-dependent protein kinase I phosphorylates DRP1 induces mitochondrial fragmentation in response to calcium influx related with neuronal activity (Yang et al., 2017). Phosphorylation at Ser-40 and Ser-44 of DRP1 mediated by glycogen synthase kinase 3β (GSK3β) can promote GTPase activity of DRP1, which increases mitochondrial division as well as neuronal apoptosis in the AD mice model (Yan et al., 2015). Phosphorylation at Ser-585 by CDK5 impairs ATP production and increases production of ROS caused by hyperactivity of DRP1, resulting in neuronal injury (Jahani-Asl et al., 2015). In addition, E3 ubiquitin ligase Parkin not only promotes DRP1 degradation through proteasome-dependent pathway(Wang et al., 2011; Tang et al., 2016), but also regulates DRP1 by S-nitrosylation(Wang et al., 2011)(Zhang et al., 2016).

p38 MAPK (mitogen-activated protein kinase) signaling is involved in a variety of intracellular responses, including inflammation, oxidative stress, reactive oxygen species (ROS) and apoptosis (Jha et al., 2015; Zhang et al., 2018; Zhou et al., 2019). Previous studies have shown that p38 MAPK signaling is essential for maintaining synaptic plasticity in the central nervous system (CNS), and excessive activation of p38 MAPK pathway in neurons are observed in neurodegenerative diseases such as AD and PD (Bohush et al., 2018; Chen et al., 2018). Our previous study also found that activation of p38 MAPK inhibits Parkin-mediated mitophagy in PD (Chen et al., 2018). In addition, p38 MAPK pathway impairs mitochondrial homeostasis (Yu et al., 2017; Bohush et al., 2018). Therefore, we proposed a hypothesis that p38 MAPK may be a vital factor involved in mitochondrial dynamics in PD.

In this study, we investigate that mitochondrial dysfunction, caused by α-synuclein aggregation, is rescued by p38 MAPK inhibition. Here we propose that DRP1 is a substrate of p38 MAPK and p38 MAPK regulates DRP1's function. Phosphorylation of DRP1 at serine 616 and its translocation to mitochondrial occur under mutant A53T α-synuclein overexpression, and inhibition of p38 MAPK reduces its phosphorylation, translocation to mitochondrial and mitochondrial fission. Our findings identify a novel mechanism that p38 MAPK contributes to α-synuclein-induced neuronal death through activating mitochondrial fission.