LIM kinase-2 induces programmed necrotic neuronal death via dysfunction of DRP1-mediated mitochondrial fission

Abstract

Although the aberrant activation of cell cycle proteins has a critical role in neuronal death, effectors or mediators of cyclin D1/ cyclin-dependent kinase 4 (CDK4)-mediated death signal are still unknown. Here, we describe a previously unsuspected role of LIM kinase 2 (LIMK2) in programmed necrotic neuronal death. Downregulation of p27 Kip1 expression by Rho kinase (ROCK) activation induced cyclin D1/CDK4 expression levels in neurons vulnerable to status epilepticus (SE). Cyclin D1/CDK4 complex subsequently increased LIMK2 expression independent of caspase-3 and receptor interacting protein kinase 1 activity. In turn, upregulated LIMK2 impaired dynamic-related protein-1 (DRP1)-mediated mitochondrial fission without alterations in cofilin phosphorylation/expression and finally resulted in necrotic neuronal death. Inhibition of LIMK2 expression and rescue of DRP1 function attenuated this programmed necrotic neuronal death induced by SE. Therefore, we suggest that the ROCK-p27 Kip1 -cyclin D1/CDK4-LIMK2-DRP1-mediated programmed necrosis may be new therapeutic targets for neuronal death. The cell cycle is essential for a vital process, including proliferation, differentiation and survival of various cells. Cell cycle progression is regulated by two classes of proteins, the cyclins and the cyclin-dependent kinases (CDKs). Among them, cyclin D1 forms a complex with CDK4 and inactivates retinoblastoma protein (Rb) through phosphorylation resulting in activating E2 promoter-binding factor (E2F) family of transcription factors. Active E2F induces various gene transcriptions involving the cell cycle. 1 In post-mitotic neurons, some pathological conditions upregulate cyclin D1/CDK4 complex expression to induce activation of E2F members that contributes to increased transcription of proapoptotic molecules. 2,3 However, it is unclear whether cyclin D1 expression directly induces neuronal death for a number of following reasons. First, due to a time lag between cyclin D1/CDK4 expression and the onset of DNA fragmentation, most cyclin D1-positive neurons show TUNEL negativity. 4,5 Second, cyclin D1 level is unaltered in cultured embryonic neurons following apoptosis induction. 6 Third, Rb phosphorylation is rarely observed in vivo, 4 although cyclin D1/CDK4 complex phosphorylates Rb protein in apoptotic cultured neurons. 6 Fourth, cyclin D1 induction following ischemia is associated with regeneration and resistance to apoptosis rather than a mediator of apoptosis. 5,7,8 Fifth, effectors or mediators of cyclin D1/CDK4-mediated death signal are still unknown. Finally, neuronal death induced by various insults is morphologically necrotic rather than apoptotic. 9-12 Therefore, it is likely that some essential factors are missing in the cyclin D/CDK4-mediated neuronal death pathway.LIM kinases (LIMK1 and LIMK2) phosphorylate cofilin that is a stimulus-responsive mediator of actin dynamics. [13][14][15] Interestingly, non-phosphorylated cofilin targets mitochondrial membranes in response to apoptotic stimuli for cytochrome c releas...

Mitochondrial network structure homeostasis and cell death

“…Eventually, inactivation of Drp1 and its mediation of mitochondrial fusion led to programmed necrotic cell death. 72 This phenomenon was also observed in mouse fibroblasts (L929 cells) that were both treated with TNFα and Drp1 inhibited pharmacologically by Mdivi-1, which resulted in reduced mitochondrial fission and enhanced necroptosis. 68 However, necroptosis has been widely demonstrated to occur independently of mitochondrial morphology.…”

“…One interesting result indicated that LIM domain kinase 2 (LIMK2) interrupted Drp1‐mediated mitochondrial fission by downregulating the phosphorylation ratio of Drp1 at Ser616/Ser637. Eventually, inactivation of Drp1 and its mediation of mitochondrial fusion led to programmed necrotic cell death . This phenomenon was also observed in mouse fibroblasts (L929 cells) that were both treated with TNF‐α and Drp1 inhibited pharmacologically by Mdivi‐1, which resulted in reduced mitochondrial fission and enhanced necroptosis .…”

A Receptor-interacting Protein 1 (RIP1)-independent Necrotic Death under the Control of Protein Phosphatase PP2A That Involves the Reorganization of Actin Cytoskeleton and the Action of Cofilin-1

“…6J). This contribution could reflect the specific generation of mitochondrial stress as recently proposed (41)(42)(43). Peculiarities in the DMNQ-induced necrosis emerged also after comparing HT29 and U87MG cells.…”

RhoA regulates Drp1 mediated mitochondrial fission through ROCK to protect cardiomyocytes

“…Previous studies suggest the involvement of ROCK in regulation of Drp1 and mitochondrial fission [24–27]. It has not been determined, however, whether Drp1 serves as a downstream mediator of RhoA signaling and is a mechanism by which receptor activation can regulate mitochondrial dynamics.…”