Does Caspase-6 Have a Role in Perinatal Brain Injury?

Leflunomide Treatment Does Not Protect Neural Cells following Oxygen-Glucose Deprivation (OGD) In Vitro

Neonatal hypoxia-ischemia (HI) affects 2-3 per 1000 live births in developed countries and up to 26 per 1000 live births in developing countries. It is estimated that of the 750,000 infants experiencing a hypoxic-ischemic event during birth per year, more than 400,000 will be severely affected. As treatment options are limited, rapidly identifying new therapeutic avenues is critical, and repurposing drugs already in clinical use offers a fast-track route to clinic. One emerging avenue for therapeutic intervention in neonatal HI is to target mitochondrial dysfunction, which occurs early in the development of brain injury. Mitochondrial dynamics are particularly affected, with mitochondrial fragmentation occurring at the expense of the pro-fusion protein Optic Atrophy (OPA)1. OPA1, together with mitofusins (MFN)1/2, are required for membrane fusion, and therefore, protecting their function may also safeguard mitochondrial dynamics. Leflunomide, an FDA-approved immunosuppressant, was recently identified as an activator of MFN2 with partial effects on OPA1 expression. We, therefore, treated C17.2 cells with Leflunomide before or after oxygen-glucose deprivation, an in vitro mimic of HI, to determine its efficacy as a neuroprotection and inhibitor of mitochondrial dysfunction. Leflunomide increased baseline OPA1 but not MFN2 expression in C17.2 cells. However, Leflunomide was unable to promote cell survival following OGD. Equally, there was no obvious effect on mitochondrial morphology or bioenergetics. These data align with studies suggesting that the tissue and mitochondrial protein profile of the target cell/tissue are critical for taking advantage of the therapeutic actions of Leflunomide.

Independent role of caspases and Bik in augmenting influenza A virus replication in airway epithelial cells and mice

Caspases and poly (ADP-ribose) polymerase 1 (PARP1) have been shown to promote influenza A virus (IAV) replication. However, the relative importance and molecular mechanisms of specific caspases and their downstream substrate PARP1 in regulating viral replication in airway epithelial cells (AECs) remains incompletely elucidated. Here, we targeted caspase 2, 3, 6, and PARP1 using specific inhibitors to compare their role in promoting IAV replication. Inhibition of each of these proteins caused significant decline in viral titer, although PARP1 inhibitor led to the most robust reduction of viral replication. We previously showed that the pro-apoptotic protein Bcl-2 interacting killer (Bik) promotes IAV replication in the AECs by activating caspase 3. In this study, we found that as compared with AECs from wild-type mice, bik-deficiency alone resulted in ~ 3 logs reduction in virus titer in the absence of treatment with the pan-caspase inhibitor (Q-VD-Oph). Inhibiting overall caspase activity using Q-VD-Oph caused additional decline in viral titer by ~ 1 log in bik-/- AECs. Similarly, mice treated with Q-VD-Oph were protected from IAV-induced lung inflammation and lethality. Inhibiting caspase activity diminished nucleo-cytoplasmic transport of viral nucleoprotein (NP) and cleavage of viral hemagglutinin and NP in human AECs. These findings suggest that caspases and PARP1 play major roles to independently promote IAV replication and that additional mechanism(s) independent of caspases and PARP1 may be involved in Bik-mediated IAV replication. Further, peptides or inhibitors that target and block multiple caspases or PARP1 may be effective treatment targets for influenza infection.

Statistical differences resulting from selection of stable reference genes after hypoxia and hypothermia in the neonatal rat brain

Real-time reverse transcription PCR (qPCR) normalized to an internal reference gene (RG), is a frequently used method for quantifying gene expression changes in neuroscience. Although RG expression is assumed to be constant independent of physiological or experimental conditions, several studies have shown that commonly used RGs are not expressed stably. The use of unstable RGs has a profound effect on the conclusions drawn from studies on gene expression, and almost universally results in spurious estimation of target gene expression. Approaches aimed at selecting and validating RGs often make use of different statistical methods, which may lead to conflicting results. Based on published RG validation studies involving hypoxia the present study evaluates the expression of 5 candidate RGs (Actb, Pgk1, Sdha, Gapdh, Rnu6b) as a function of hypoxia exposure and hypothermic treatment in the neonatal rat cerebral cortex–in order to identify RGs that are stably expressed under these experimental conditions–using several statistical approaches that have been proposed to validate RGs. In doing so, we first analyzed RG ranking stability proposed by several widely used statistical methods and related tools, i.e. the Coefficient of Variation (CV) analysis, GeNorm, NormFinder, BestKeeper, and the ΔCt method. Using the Geometric mean rank, Pgk1 was identified as the most stable gene. Subsequently, we compared RG expression patterns between the various experimental groups. We found that these statistical methods, next to producing different rankings per se, all ranked RGs displaying significant differences in expression levels between groups as the most stable RG. As a consequence, when assessing the impact of RG selection on target gene expression quantification, substantial differences in target gene expression profiles were observed. Altogether, by assessing mRNA expression profiles within the neonatal rat brain cortex in hypoxia and hypothermia as a showcase, this study underlines the importance of further validating RGs for each individual experimental paradigm, considering the limitations of the statistical methods used for this aim.

DNA Damage Response and Repair, DNA Methylation, and Cell Death in Human Neurons and Experimental Animal Neurons Are Different

Neurological disorders affecting individuals in infancy to old age elude interventions for meaningful protection against neurodegeneration, and preclinical work has not translated to humans. We studied human neuron responses to injury and death stimuli compared to those of animal neurons in culture under similar settings of insult (excitotoxicity, oxidative stress, and DNA damage). Human neurons were differentiated from a cortical neuron cell line and the embryonic stem cell-derived H9 line. Mouse neurons were differentiated from forebrain neural stem cells and embryonic cerebral cortex; pig neurons were derived from forebrain neural stem cells. Mitochondrial morphology was different in human and mouse neurons. Human and mouse neurons challenged with DNA-damaging agent camptothecin showed different chromatin condensation, cell death, and DNA damage sensor activation. DNA damage accumulation and repair kinetics differed among human, mouse, and pig neurons. Promoter CpG island methylation microarrays showed significant differential DNA methylation in human and mouse neurons after injury. Therefore, DNA damage response, DNA repair, DNA methylation, and autonomous cell death mechanisms in human neurons and experimental animal neurons are different.

Constitutive ablation of caspase-6 reduces the inflammatory response and behavioural changes caused by peripheral pro-inflammatory stimuli

Traditionally, the family of caspases has been subcategorised according to their respective main roles in mediating apoptosis or inflammation. However, recent studies have revealed that caspases participate in diverse cellular functions beyond their canonical roles. Caspase-6 (C6) is one such protease known for its role as a pro-apoptotic executioner caspase and its aberrant activity in several neurodegenerative diseases. In addition to apoptosis, C6 has been shown to regulate B-cell activation and differentiation in plasma cells as well as macrophage activation. Furthermore, C6 has recently been postulated to play a role in mediating the inflammatory response through the production of TNF-α. In this study we further examine the role of C6 in mediating the inflammatory response and its contribution to the manifestation of behavioural abnormalities in mice. We find that C6 is a positive regulator of TNF-α transcription in macrophages and that ablation of C6 reduces lipopolysaccharide (LPS)-induced TNF-α levels in plasma. Furthermore, loss of C6 attenuates LPS-induced behavioural changes in mice and protects neurons from cytokine-mediated toxicity. These data further support the involvement of C6 in the inflammatory response and point to a previously unknown role for C6 in the pathophysiology of depression.

Microarray Profiling and Co-Expression Network Analysis of LncRNAs and mRNAs in Neonatal Rats Following Hypoxic-ischemic Brain Damage

Long noncoding RNAs (lncRNAs) play critical roles in cellular homeostasis. However, little is known about their effect in developing rat brains with hypoxic-ischemic brain damage (HIBD). To explore the expression and function of lncRNA in HIBD, we analyzed the expression profiles of lncRNAs in hypoxic-ischemic (HI) brains and sham control using microarray analysis. The results showed a remarkable difference in lncRNA between HI and sham brains. A total of 322 lncRNAs were found to be differentially expressed in HI brains, compared to sham control. Among these, BC088414 was one of the most significantly urpregulated lncRNAs. In addition, 375 coding genes were differentially expressed between HI brains and sham control. Pathway and gene ontology analysis indicated that the upregulated coding genes mostly involved in wounding, inflammation and defense, whereas the downregulated transcripts were largely associated with neurogenesis and repair. Moreover, coding non-coding co-expression network analysis showed that the BC088414 lncRNA expression was correlated with apoptosis-related genes, including Casp6 and Adrb2. Silencing of lncRNA BC088414 in PC12 cells caused reduced mRNA level of Casp6 and Adrb2, decreased cell apoptosis and increased cell proliferation. These results suggested lncRNA might participate in the pathogenesis of HIBD via regulating coding genes.