Inhibition of Drp1 provides neuroprotection in vitro and in vivo

Abstract

Impaired regulation of mitochondrial dynamics, which shifts the balance towards fission, is associated with neuronal death in age-related neurodegenerative diseases, such as Alzheimer's disease or Parkinson's disease. A role for mitochondrial dynamics in acute brain injury, however, has not been elucidated to date. Here, we investigated the role of dynamin-related protein 1 (Drp1), one of the key regulators of mitochondrial fission, in neuronal cell death induced by glutamate toxicity or oxygen-glucose deprivation (OGD) in vitro, and after ischemic brain damage in vivo. Drp1 siRNA and small molecule inhibitors of Drp1 prevented mitochondrial fission, loss of mitochondrial membrane potential (MMP), and cell death induced by glutamate or tBid overexpression in immortalized hippocampal HT-22 neuronal cells. Further, Drp1 inhibitors protected primary neurons against glutamate excitotoxicity and OGD, and reduced the infarct volume in a mouse model of transient focal ischemia. Our data indicate that Drp1 translocation and associated mitochondrial fission are key features preceding the loss of MMP and neuronal cell death. Thus, inhibition of Drp1 is proposed as an efficient strategy of neuroprotection against glutamate toxicity and OGD in vitro and ischemic brain damage in vivo. Mitochondria play crucial roles in energy metabolism, regulation of free radical formation and calcium storage, thereby determining essential metabolic functions and cell survival. 1 Further, mitochondria are highly dynamic organelles that undergo constant fission and fusion and these morphological changes are required for efficient ATP production, calcium buffering, regulation of signal transduction and apoptosis. 2 In neurons, mitochondrial fission is also essential for axonal transport of the organelles into areas of high metabolic demand, 3 whereas mitochondrial fusion supports substitution and regeneration of mitochondrial proteins, mtDNA repair and functional recovery. 2,4 Consistent with the critical roles of mitochondrial dynamics in neurons, defects in mitochondrial fission and fusion proteins are associated with a wide array of inherited or acquired neurodegenerative diseases such as Charcot-Marie-Tooth disease or Alzheimer's disease, respectively. 2 Fission and fusion defects may limit mitochondrial motility, decrease energy production, promote oxidative stress and lead to accumulating of mtDNA defects, thereby promoting neuronal dysfunction and cell death. 1 Recently, enhanced mitochondrial fragmentation was associated with induction of neuronal death triggered by oxidative stress. 5 These data imply that during neuronal cell death, the tubular mitochondrial network is fragmented into smaller and functionally impaired organelles. 5 It is, however, a matter of ongoing controversy, whether mitochondrial fragmentation is cause or consequence in programmed cell death.Current knowledge of the mechanisms regulating mitochondrial dynamics indicates that fission and fusion of mitochondria are under control of highly conserved dynamin-relate...

Mitochondrial dynamics in neuronal injury, development and plasticity

“…Drp1 has been put forward as a drug target for preventing mitochondrial fragmentation under diverse pathological conditions (Rosdah et al, 2016). Indeed, currently available Drp1 inhibitors have shown neuroprotective properties in animal models of HD (Guo et al, 2013b), PD (Hatch et al, 2014;Filichia et al, 2016) and ischemic stroke (Grohm et al, 2012;Li et al, 2015;Zhang et al, 2013). However, given the widespread expression of the fission enzyme and the detrimental consequences on the development and function of the nervous system upon deletion of Drp1, targeting neuron-specific regulators of Drp1 or other components of the mitochondrial fission/fusion machinery are potentially safer therapeutic strategies.…”

“…In vitro models of cerebral ischemia confirm these findings, as glutamate excitotoxicity (Kumari et al, 2012;Niizuma et al, 2010) and hypoxia (Sanderson et al, 2015) on their own can induce mitochondrial fragmentation. The relationship between mitochondrial fission and ischemic injury appears more than correlative, as inhibition of Drp1 with the small-molecule inhibitor mdivi-1 was shown by several groups to decrease infarct volume following MCAO (Grohm et al, 2012;Li et al, 2015;Zhang et al, 2013). However, a number of surprising observations question the interpretation that inhibition of Drp1 protects neurons from ischemic death by preventing mitochondrial fission.…”

Aberrant Mitochondrial Fission Is Maladaptive in Desmin Mutation–Induced Cardiac Proteotoxicity

“…Mdivi‐1 was reported to inhibit the activity of the mitochondrial fission regulator Drp1 and also impedes apoptosis early in the intrinsic pathway by blocking Bax/Bak‐dependent mitochondrial outer membrane permeabilization 33. Moreover, studies also showed that mdivi‐1 also blocks pro‐apoptotic Bax‐dependent cytochrome C release from isolated mitochondria33 and attenuates neural cell death in vitro and in vivo 56, 57. In the current study, we found that mdivi‐1 inhibited Drp1‐mediated mitochondrial fission, decreased Bax expression, and significantly improved mitochondrial respiration, resulting in decreased cell death induced by D7‐Des in cardiomyocytes.…”

Vitamin D-binding protein interacts with Aβ and suppresses Aβ-mediated pathology

“…The degree of cell viability or cell survival was measured using the MTT assay, MTS assay, and DAPI staining as described previously. [51][52][53] The relative reduction of MTT and MTS was quantified by measuring optical density at 560 nm using a plate reader (Bio-Tek Instruments, Winooski, VT, USA). DAPIstained cells are counted using Image-Pro Plus Version 6.0 (Media Cybernetics, Bethesda, MD, USA).…”