CDDO-Me Selectively Attenuates CA1 Neuronal Death Induced by Status Epilepticus via Facilitating Mitochondrial Fission Independent of LONP1

Abstract

2-Cyano-3,12-dioxo-oleana-1,9(11)-dien-28-oic acid methyl ester (CDDO-Me) is a triterpenoid analogue of oleanolic acid that exhibits promising anti-cancer, anti-inflammatory, antioxidant and neuroprotective activities. In addition, CDDO-Me affects cellular differentiation and cell cycle arrest, and irreversibly inhibits Lon protease-1 (LONP1). In the present study, we evaluate the effects of CDDO-Me on mitochondrial dynamics and its downstream effectors in order to understand the underlying mechanism of the neuronal death following status epilepticus (SE, a prolonged seizure activity). CDDO-Me increased dynamin-related proteins 1 (DRP1)-serine 616 phosphorylation via activating extracellular-signal-regulated kinase 1/2 (ERK1/2) and c-Jun N-terminal kinase (JNK), but not protein kinase A (PKA) or protein phosphatases (PPs). In addition, CDDO-Me facilitated DRP1-mediated mitochondrial fissions, which selectively attenuated SE-induced CA1 neuronal death. Unlike CDDO-Me, LONP1 knockdown led to SE-induced massive degeneration of dentate granule cells, CA1 neurons and hilus interneurons without altering the expression and phosphorylation of DRP1, ERK1/2, JNK and PP2B. LONP1 knockdown could not inhibit SE-induced mitochondrial elongation in CA1 neurons. Co-treatment of CDDO-Me with LONP1 siRNA ameliorated only CA1 neuronal death, concomitant with abrogation of mitochondrial elongation induced by SE. Thus, our findings suggest that CDDO-Me may selectively attenuate SE-induced CA1 neuronal death by rescuing the abnormal mitochondrial machinery, independent of LONP1 activity.

CDDO-Me Distinctly Regulates Regional Specific Astroglial Responses to Status Epilepticus via ERK1/2-Nrf2, PTEN-PI3K-AKT and NFκB Signaling Pathways

“…Under physiological conditions, CDDO-Me increased Nrf2 expression in the whole hippocampus ( p < 0.05 vs. vehicle, one-way ANOVA followed by Newman–Keuls post hoc test; n = 7, respectively; Figure 1 A,B and Supplementary Figure S1 ). Consistent with our previous study [ 28 ], CDDO-Me did not affect the seizure latency and its severity in response to pilocarpine (repeated one-way ANOVA; n = 7; Figure 1 C,D). Following SE, total Nrf2 expression was decreased in the whole hippocampus ( p < 0.05 vs. vehicle, one-way ANOVA followed by Newman–Keuls post hoc test; n = 7, respectively; Figure 1 A,B and Supplementary Figure S1 ).…”

“…Thereafter, an infusion kit was connected with an Alzet 1007D osmotic pump (Alzet, Cupertino, CA, USA) containing (1) vehicle, (2) CDDO-Me (10 μM), (3) 3-chloroacetyl-indole (3CAI, an AKT inhibitor, 25 μM), (4) SC79 (an AKT activator, 25 μM), and (5) CDDO-Me + U0126 (an ERK1/2 inhibitor, 25 μM), which were continuously infused in each group over a 7-day period. Consistent with our previous studies [ 28 , 29 , 30 ], the concentration of each compound (3CAI, SC79, and U0126) did not led to behavioral and neurological abnormality in animals and alterations in seizure threshold in response to pilocarpine. The pump was placed in a subcutaneous pocket in the interscapular region.…”

“…The time point starting paroxysmal discharges that showed 4–10 Hz with 2 times higher amplitude than the basal level and lasted more than 3 s was defined as the time of seizure on-set. Spectrograms were automatically made by a Hanning sliding window with a 50% overlap [ 28 , 29 ].…”

“…In addition, CDDO-Me has antioxidant properties, since it activates nuclear factor-erythroid 2-related factor 2 (Nrf2, a redox-sensitive transcription factor) that regulates the expression of antioxidant defense enzymes mediated by antioxidant-response element (ARE)-dependent transcription. Thus, CDDO-Me protects neurons and astrocytes from various harmful stresses including SE through the maintenance of redox homeostasis [ 26 , 27 , 28 , 29 ]. Furthermore, CDDO-Me distinctly affects activities of various signaling molecules, such as extracellular-signal-regulated kinase 1/2 (ERK1/2), nuclear factor-κB (NFκB), phosphatidylinositol-3-kinase (PI3K), and AKT [ 28 , 29 ].…”

“…Thus, CDDO-Me protects neurons and astrocytes from various harmful stresses including SE through the maintenance of redox homeostasis [ 26 , 27 , 28 , 29 ]. Furthermore, CDDO-Me distinctly affects activities of various signaling molecules, such as extracellular-signal-regulated kinase 1/2 (ERK1/2), nuclear factor-κB (NFκB), phosphatidylinositol-3-kinase (PI3K), and AKT [ 28 , 29 ]. Interestingly, these signaling cascades are involved in astroglial responses to SE.…”