Neuroprotective effects of crude extract of Crataegus songarica on a rat model of traumatic brain injury

Purpose: To investigate the protective effect of Crataegus songarica extract (CSCE) against traumatic brain injury (TBI) in rats, and the underlying mechanism of action. Methods: A rat model of TBI was established via tracheal intubation procedure, and the rats were treated with graded doses of CSCE. Neuronal survival was determined by Nissl staining, while neuronal apoptosis was measured using TUNEL-staining. Neurological impairments were determined based on neurological severity score (NSS). Results: Treatment of TBI rats with CSCE enhanced neuronal survival and decreased TUNEL-positive cell fraction in the brain cortex. The treatment prevented elevation of NSS and suppressed mRNA and protein expression levels of IL-6 and TNF-α in brain cortex. Moreover, CSCE treatment prevented TBI-mediated suppression of activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx), and attenuated hydrogen peroxide (H2O2) levels in TBI rat brain cortex. Treatment of TBI rats with CSCE down-regulated NF-κB expression, increased Nrf2 expression and up-regulated mRNA expressions of heme oxygenase 1 (HO-1) and quinine oxidoreductase 1 (NQO-1). Conclusion: These results suggest that CSCE prevents TBI-mediated reduction in neuronal survival and inhibits brain cortical neuronal death in rats. It improves NSS and inhibits inflammatory response via activation of Nrf2 pathway and targeting of NF-κB expression. Therefore, CSCE is a potential therapeutic agent for TBI.

Mitofusin 2 Integrates Mitochondrial Network Remodelling, Mitophagy and the Renewal of Respiratory Chain Proteins in Neurons After Oxygen and Glucose Deprivation.

In the efforts to develop effective therapeutic strategies limiting post-ischemic injury, mitochondria emerge as key element in determining the fate of the neurons. Mitochondrial damage can be alleviated by various mechanisms including mitochondrial network remodelling, mitochondrial elimination and mitochondrial protein biogenesis. However, the mechanisms regulating the relationship between these phenomena are poorly understood. Here we hypothesize that mitofusin 2 (Mfn2), a mitochondrial GTPase, involved in mitochondrial fusion, mitochondria trafficking and mitochondria and endoplasmic reticulum (ER) tethering, may act as a linking and regulatory factor in neurons following ischemic insult. To verify this assumption, we performed a temporal oxygen and glucose deprivation (OGD) on rat cortical primary culture to determine whether Mfn2 protein reduction may affect the onset of mitophagy, subsequent mitochondrial biogenesis and thus neuronal survival. In our study we found that Mfn2 knock-down increased the susceptibility of the neurons to the OGD. Mfn2 protein reduction prevented mitochondrial network remodelling and resulted in the prolonged mitophagosomes formation in response to the insult. Further on, Mfn2 protein reduction was accompanied by a reduced level of Parkin protein and an increased Parkin accumulation with mitochondria. As for Mfn2-expressing neurons, the OGD insult was followed by an elevated mtDNA content and an increase in the respiratory chain proteins. Neither of this phenomena were observed for Mfn2-reduced neurons. Collectively, our findings show that Mfn2 in neurons is involved in their response to mild and transient OGD stress, balancing the extent of elimination of defective mitochondria and positively influencing mitochondrial respiratory proteins levels. Our study confirms that Mfn2 is an essential element of the neuronal response to ischemic insult, necessary for the neuronal survival.

DTYMK is essential for genome integrity and neuronal survival

Nucleotide metabolism is a complex pathway regulating crucial cellular processes such as nucleic acid synthesis, DNA repair and proliferation. This study shows that impairment of the biosynthesis of one of the building blocks of DNA, dTTP, causes a severe, early-onset neurodegenerative disease. Here, we describe two unrelated children with bi-allelic variants in DTYMK, encoding dTMPK, which catalyzes the penultimate step in dTTP biosynthesis. The affected children show severe microcephaly and growth retardation with minimal neurodevelopment. Brain imaging revealed severe cerebral atrophy and disappearance of the basal ganglia. In cells of affected individuals, dTMPK enzyme activity was minimal, along with impaired DNA replication. In addition, we generated dtymk mutant zebrafish that replicate this phenotype of microcephaly, neuronal cell death and early lethality. An increase of ribonucleotide incorporation in the genome as well as impaired responses to DNA damage were observed in dtymk mutant zebrafish, providing novel pathophysiological insights. It is highly remarkable that this deficiency is viable as an essential component for DNA cannot be generated, since the metabolic pathway for dTTP synthesis is completely blocked. In summary, by combining genetic and biochemical approaches in multiple models we identified loss-of-function of DTYMK as the cause of a severe postnatal neurodegenerative disease and highlight the essential nature of dTTP synthesis in the maintenance of genome stability and neuronal survival.

Two-Chains Tissue Plasminogen Activator Unifies Met and NMDA Receptor Signalling to Control Neuronal Survival

Tissue-type plasminogen activator (tPA) plays roles in the development and the plasticity of the nervous system. Here, we demonstrate in neurons, that by opposition to the single chain form (sc-tPA), the two-chains form of tPA (tc-tPA) activates the MET receptor, leading to the recruitment of N-Methyl-D-Aspartate receptors (NMDARs) and to the endocytosis and proteasome-dependent degradation of NMDARs containing the GluN2B subunit. Accordingly, tc-tPA down-regulated GluN2B-NMDAR-driven signalling, a process prevented by blockers of HGFR/MET and mimicked by its agonists, leading to a modulation of neuronal death. Thus, our present study unmasks a new mechanism of action of tPA, with its two-chains form mediating a crosstalk between MET and the GluN2B subunit of NMDARs to control neuronal survival.