Nuclear Ca(++)-influx, Ca (++)/calmodulin-dependent protein kinase IV activity and CREB protein phosphorylation during post-hypoxic reoxygenation in neuronal nuclei of newborn piglets: the role of nitric oxide

Neuroprotective effect of Src kinase in hypoxia-ischemia: A systematic review

Background

Hypoxic-ischemic encephalopathy (HIE) is a major cause of neonatal morbidity and mortality worldwide. While the application of therapeutic hypothermia has improved neurodevelopmental outcomes for some survivors of HIE, this lone treatment option is only available to a subset of affected neonates. Src kinase, an enzyme central to the apoptotic cascade, is a potential pharmacologic target to preserve typical brain development after HIE. Here, we present evidence of the neuroprotective effects of targeting Src kinase in preclinical models of HIE.

Methods

We performed a comprehensive literature search using the National Library of Medicine's MEDLINE database to compile studies examining the impact of Src kinase regulation on neurodevelopment in animal models. Each eligible study was assessed for bias.

Results

Twenty studies met the inclusion criteria, and most studies had an intermediate risk for bias. Together, these studies showed that targeting Src kinase resulted in a neuroprotective effect as assessed by neuropathology, enzymatic activity, and neurobehavioral outcomes.

Conclusion

Src kinase is an effective neuroprotective target in the setting of acute hypoxic injury. Src kinase inhibition triggers multiple signaling pathways of the sub-membranous focal adhesions and the nucleus, resulting in modulation of calcium signaling and prevention of cell death. Despite the significant heterogeneity of the research studies that we examined, the available evidence can serve as proof-of-concept for further studies on this promising therapeutic strategy.

Computational analysis of cortical neuronal excitotoxicity in a large animal model of neonatal brain injury

BACKGROUND

Neonatal hypoxic brain injury is a major cause of intellectual and developmental disability. Hypoxia causes neuronal dysfunction and death in the developing cerebral cortex due to excitotoxic Ca²⁺-influx. In the translational piglet model of hypoxic encephalopathy, we have previously shown that hypoxia overactivates Ca²⁺/Calmodulin (CaM) signaling via Sarcoma (Src) kinase in cortical neurons, resulting in overexpression of proapoptotic genes. However, identifying the exact relationship between alterations in neuronal Ca²⁺-influx, molecular determinants of cell death, and the degree of hypoxia in a dynamic system represents a significant challenge.

METHODS

We used experimental and computational methods to identify molecular events critical to the onset of excitotoxicity-induced apoptosis in the cerebral cortex of newborn piglets. We used 2-3-day-old piglets (normoxic [Nx], hypoxic [Hx], and hypoxic + Src-inhibitor-treatment [Hx+PP2] groups) for biochemical analysis of ATP production, Ca²⁺-influx, and Ca²⁺/CaM-dependent protein kinase kinase 2 (CaMKK2) expression. We then used SimBiology to build a computational model of the Ca²⁺/CaM-Src-kinase signaling cascade, simulating Nx, Hx, and Hx+PP2 conditions. To evaluate our model, we used Sobol variance decomposition, multiparametric global sensitivity analysis, and parameter scanning.

RESULTS

Our model captures important molecular trends caused by hypoxia in the piglet brain. Incorporating the action of Src kinase inhibitor PP2 further validated our model and enabled predictive analysis of the effect of hypoxia on CaMKK2. We determined the impact of a feedback loop related to Src phosphorylation of NMDA receptors and activation kinetics of CaMKII. We also identified distinct modes of signaling wherein Ca²⁺ level alterations following Src kinase inhibition may not be a linear predictor of changes in Bax expression. Importantly, our model indicates that while pharmacological pre-treatment significantly reduces the onset of abnormal Ca²⁺-influx, there exists a window of intervention after hypoxia during which targeted modulation of Src-NMDAR interaction kinetics in combination with PP2 administration can reduce Ca²⁺-influx and Bax expression to similar levels as pre-treatment.

CONCLUSIONS

Our model identifies new dynamics of critical components in the Ca²⁺/CaM-Src signaling pathway leading to neuronal injury and provides a feasible framework for drug efficacy studies in translational models of neonatal brain injury for the prevention of intellectual and developmental disabilities.

Apoptotic cell death and altered calcium homeostasis caused by frataxin depletion in dorsal root ganglia neurons can be prevented by BH4 domain of Bcl-xL protein

Friedreich ataxia (FRDA) is a neurodegenerative disease characterized by a decreased expression of the mitochondrial protein frataxin. Major neurological symptoms of the disease are due to degeneration of dorsal root ganglion (DRG) sensory neurons. In this study we have explored the neurodegenerative events occurring by frataxin depletion on primary cultures of neurons obtained from rat DRGs. Reduction of 80% of frataxin levels in these cells was achieved by transduction with lentivirus containing shRNA silencing sequences. Frataxin depletion caused mitochondrial membrane potential decrease, neurite degeneration and apoptotic cell death. A marked increase of free intracellular Ca(2+) levels and alteration in Ca(2+)-mediated signaling pathways was also observed, thus suggesting that altered calcium homeostasis can play a pivotal role in neurodegeneration caused by frataxin deficiency. These deleterious effects were reverted by the addition of a cell-penetrant TAT peptide coupled to the BH4, the anti-apoptotic domain of Bcl-x(L). Treatment of cultured frataxin-depleted neurons with TAT-BH4 was able to restore the free intracellular Ca(2+) levels and protect the neurons from degeneration. These observations open the possibility of new therapies of FRDA based on modulating the Ca(2+) signaling and prevent apoptotic process to protect DRG neurons from neurodegeneration.

Prenatal hypoxic-ischemic insult changes the distribution and number of NADPH-diaphorase cells in the cerebellum

Astrogliosis, oligodendroglial death and motor deficits have been observed in the offspring of female rats that had their uterine arteries clamped at the 18^th gestational day. Since nitric oxide has important roles in several inflammatory and developmental events, here we evaluated NADPH-diaphorase (NADPH-d) distribution in the cerebellum of rats submitted to this hypoxia-ischemia (HI) model. At postnatal (P) day 9, Purkinje cells of SHAM and non-manipulated (NM) animals showed NADPH-d+ labeling both in the cell body and dendritic arborization in folia 1 to 8, while HI animals presented a weaker labeling in both cellular structures. NADPH-d+ labeling in the molecular (ML), and in both the external and internal granular layer, was unaffected by HI at this age. At P23, labeling in Purkinje cells was absent in all three groups. Ectopic NADPH-d+ cells in the ML of folia 1 to 4 and folium 10 were present exclusively in HI animals. This labeling pattern was maintained up to P90 in folium 10. In the cerebellar white matter (WM), at P9 and P23, microglial (ED1+) NADPH-d+ cells, were observed in all groups. At P23, only HI animals presented NADPH-d labeling in the cell body and processes of reactive astrocytes (GFAP+). At P9 and P23, the number of NADPH-d+ cells in the WM was higher in HI animals than in SHAM and NM ones. At P45 and at P90 no NADPH-d+ cells were observed in the WM of the three groups. Our results indicate that HI insults lead to long-lasting alterations in nitric oxide synthase expression in the cerebellum. Such alterations in cerebellar differentiation might explain, at least in part, the motor deficits that are commonly observed in this model.

Hypoxia-ischemia and retinal ganglion cell damage

Retinal hypoxia is the potentially blinding mechanism underlying a number of sight-threatening disorders including central retinal artery occlusion, ischemic central retinal vein thrombosis, complications of diabetic eye disease and some types of glaucoma. Hypoxia is implicated in loss of retinal ganglion cells (RGCs) occurring in such conditions. RGC death occurs by apoptosis or necrosis. Hypoxia-ischemia induces the expression of hypoxia inducible factor-1α and its target genes such as vascular endothelial growth factor (VEGF) and nitric oxide synthase (NOS). Increased production of VEGF results in disruption of the blood retinal barrier leading to retinal edema. Enhanced expression of NOS results in increased production of nitric oxide which may be toxic to the cells resulting in their death. Excess glutamate release in hypoxic-ischemic conditions causes excitotoxic damage to the RGCs through activation of ionotropic and metabotropic glutamate receptors. Activation of glutamate receptors is thought to initiate damage in the retina by a cascade of biochemical effects such as neuronal NOS activation and increase in intracellular Ca²⁺ which has been described as a major contributing factor to RGC loss. Excess production of proinflammatory cytokines also mediates cell damage. Besides the above, free-radicals generated in hypoxic-ischemic conditions result in RGC loss because of an imbalance between antioxidant- and oxidant-generating systems. Although many advances have been made in understanding the mediators and mechanisms of injury, strategies to improve the damage are lacking. Measures to prevent neuronal injury have to be developed.

A Key role for cyclic AMP-responsive element binding protein in hypoxia-mediated activation of the angiogenesis factor CCN1 (CYR61) in Tumor cells

Hypoxia is a prominent feature of solid tumors known to contribute to malignant progression and therapeutic resistance. Cancer cells adapt to hypoxia using various pathways, allowing tumors to thrive in a low oxygen state. Induction of new blood vessel formation via the secretion of proangiogenic factors is one of the main adaptive responses engaged by tumor cells under hypoxic conditions. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that plays a pivotal role in mediating such responses. In addition, several other transcription factors have also been implicated in hypoxic gene regulation, either independently or in cooperation with HIF-1. In this work, we show that the expression of the angiogenesis-related, immediate early gene CCN1 (formerly known as CYR61), considered to be involved in tumor growth and invasiveness, is enhanced upon hypoxia stress primarily in a protein kinase A and cyclic AMP-responsive element binding protein (CREB) and CRE-dependent manner in various cell lines. The hypoxia-mediated activation of the CCN1 promoter is independent of HIF-1 and HIF-2, as shown by small interfering RNA knockdown. We identify the cis element in the mouse CCN1 promoter responsible for CREB binding to be one of two partial CRE sites present in the promoter. Moreover, we report for the first time that CREB-mediated CCN1 transcription is enhanced in hypoxic regions of tumors in vivo. Identifying and characterizing the molecular mechanisms that govern the response of tumors to hypoxia may be instrumental to identify the tumors that will respond favorably to inhibition of angiogenesis and thus lead to the development of treatments that could complement hypoxia-inducing treatment modalities.

Mechanism of Ca2+-influx and Ca2+/calmodulin-dependent protein kinase IV activity during in utero hypoxia in cerebral cortical neuronal nuclei of the guinea pig fetus at term

Previously we showed that following hypoxia there is an increase in nuclear Ca(2+)-influx and Ca(2+)/calmodulin-dependent protein kinase IV activity (CaMK IV) in the cerebral cortex of term guinea pig fetus. The present study tests the hypothesis that clonidine administration will prevent hypoxia-induced increased neuronal nuclear Ca(2+)-influx and increased CaMK IV activity, by blocking high-affinity Ca(2+)-ATPase. Studies were conducted in 18 pregnant guinea pigs at term, normoxia (Nx, n=6), hypoxia (Hx, n=6) and clonidine with Hx (Hx+Clo, n=6). The pregnant guinea pig was exposed to a decreased FiO(2) of 0.07 for 60 min. Clonidine, an imidazoline inhibitor of high-affinity Ca(2+)-ATPase, was administered 12.5 microg/kg IP 30 min prior to hypoxia. Hypoxia was determined biochemically by ATP and phosphocreatine (PCr) levels. Nuclei were isolated and ATP-dependent (45)Ca(2+)-influx was determined. CaMK IV activity was determined by (33)P-incorporation into syntide 2 for 2 min at 37 degrees C in a medium containing 50mM HEPES (pH 7.5), 2mM DTT, 40muM syntide 2, 0.2mM (33)P-ATP, 10mM magnesium acetate, 5 microM PKI 5-24, 2 microM PKC 19-36 inhibitor peptides, 1 microM microcystine LR, 200 microM sodium orthovanadate and either 1mM EGTA (for CaMK IV-independent activity) or 0.8mM CaCl(2) and 1mM calmodulin (for total activity). ATP (mumoles/gbrain) values were significantly different in the Nx (4.62+/-0.2), Hx (1.65+/-0.2, p<0.05 vs. Nx), and Hx+Clo (1.92+/-0.6, p<0.05 vs. Nx). PCr (mumoles/g brain) values in the Nx (3.9+/-0.1), Hx (1.10+/-0.3, p<0.05 vs. Nx), and Hx+Clo (1.14+/-0.3, p<0.05 vs. Nx). There was a significant difference between nuclear Ca(2+)-influx (pmoles/mg protein/min) in Nx (3.98+/-0.4), Hx (10.38+/-0.7, p<0.05 vs. Nx), and Hx+Clo (7.35+/-0.9, p<0.05 vs. Nx, p<0.05 vs. Hx), and CaM KIV (pmoles/mg protein/min) in Nx (1314.00+/-195.4), Hx (2315.14+/-148.5, p<0.05 vs. Nx), and Hx+Clo (1686.75+/-154.3, p<0.05 vs. Nx, p<0.05 vs. Hx). We conclude that the mechanism of hypoxia-induced increased nuclear Ca(2+)-influx is mediated by high-affinity Ca(2+)-ATPase and that CaMK IV activity is nuclear Ca(2+)-influx-dependent. We speculate that hypoxia-induced alteration of high-affinity Ca(2+)-ATPase is a key step that triggers nuclear Ca(2+)-influx, leading to CREB protein-mediated increased expression of apoptotic proteins and hypoxic neuronal death.