Chemical preconditioning in mice is not mediated by upregulation of nitric oxide synthase isoforms

Inhibiting Sphingosine 1-Phosphate Receptor Subtype 3 Attenuates Brain Damage During Ischemia-Reperfusion Injury by Regulating nNOS/NO and Oxidative Stress

Background

Ischemic stroke (IS) is a common disease endangering human life and health. Cerebral ischemia triggers a series of complex harmful events, including excitotoxicity, inflammation and cell death, as well as increased nitric oxide production through the activation of nitric oxide synthase (NOS). Oxidative stress plays a major role in cerebral ischemia and reperfusion. Sphingosine 1-phosphate receptor subtype 3 (S1PR3), a member of S1P’s G protein-coupled receptors S1PR1-S1PR5, is involved in a variety of biological effects in the body, and its role in regulating oxidative stress during cerebral ischemia and reperfusion is still unclear.

Methods

Transient middle cerebral artery occlusion (tMCAO) mice were selected as the brain ischemia–reperfusion (I/R) injury model. Male C57/BL6 mice were treated with or without a selective S1PR3 inhibition after tMCAO, and changes in infarct volume, Nissl staining, hematoxylin-eosin (H&E) staining and NOS protein, nitric oxide (NO), superoxide dismutase (SOD), and malondialdehyde (MDA) content after tMCAO were observed.

Results

In the cerebral ischemia–reperfusion model, inhibition of S1PR3 improved the infarct volume and neuronal damage in mice after tMCAO. Similarly, inhibition of S1PR3 can reduce the expression of NO synthase subtype neuronal NOS (nNOS) and reduce the production of NO after cerebral ischemia. After cerebral ischemia and reperfusion, the oxidative stress response was enhanced, and after the administration of the S1PR3 inhibitor, the SOD content increased and the MDA content decreased, indicating that S1PR3 plays an important role in regulating oxidative stress response.

Conclusion

Inhibiting S1PR3 attenuates brain damage during I/R injury by regulating nNOS/NO and oxidative stress, which provides a potential new therapeutic target and mechanism for the clinical treatment of IS.

Age- and sex-differences in the nitric oxide synthase expression and dopamine concentration in the murine model of Parkinson's disease induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

Parkinson's disease (PD) is an age- and sex-related neurodegenerative disorder of unknown aetiology. The involvement of nitric oxide synthase (NOS) in the etiopathogenesis of PD is quite well documented. We decided to examine changes in dopamine (DA) levels as well as iNOS, nNOS, eNOS mRNA and protein expression in the striatum of C57BL male and female (2- and 12-month old) mice in the course of PD-related neurodegeneration induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The significantly decreased level of DA was previously observed in male than in female, irrespective of age. In young mice the recovery of DA was significantly greater in female compared to male mice. On the contrary, both in male and female old animals the low concentration of DA was extended up to 21 days post MPTP injection. The increases in iNOS protein expression post MPTP intoxication occurred more rapidly in male (young and old) than in female mice. The pattern of changes in iNOS protein expression was also different in young versus aged mice. nNOS protein expression increased earlier in young male than young female mice. No changes were observed in eNOS expression. In conclusion, our results support the hypothesis of the involvement of iNOS and nNOS, but not eNOS in neurodegenerative processes. Our findings suggest that age- and sex-differences in DA concentration and iNOS expression as well as sex-differences of nNOS expression after intoxication may depend on the increased susceptibility of males as well as older animals to toxic effect of MPTP and aggravated process of recovery in old brains.

Mechanisms of hypoxic tolerance in presymptomatic APP23 transgenic mice

In the B6-Tg (ThylAPP)23Sdz (APP23tg) transgenic mouse model of Alzheimer's disease hypoxic tolerance is impaired prior to amyloid deposition. We therefore investigated mechanisms known to mediate resistance to hypoxic episodes in presymptomatic APP23tg and appropriate control strains. The mRNA expression levels in the hippocampus of adenosine receptor subtypes A1 and A3, estrogen receptors alpha and beta, progesterone receptor, and neuronal and endothelial nitric oxide synthase were investigated with semi-quantitative RT-PCR. Mice were pretreated in vivo with a low dose of 3-nitropropionate, an inhibitor of succinic dehydrogenase, known to mediate hypoxic tolerance within 1h. We found increased expression levels in presymptomatic, untreated APP23tg animals of adenosine A3 receptor mRNA and estrogen receptor alpha mRNA. In addition, we observed an increase in nNOS expression levels upon mild cellular hypoxia induced by 3-NP in transgenic but not in wild-type animals. We conclude that overexpression of human APP results in differential expression of receptors conferring hypoxic tolerance prior to amyloid deposition. Up-regulation of nNOS expression levels upon hypoxic challenge in APP23tg transgenic animals may therefore reflect a selective vulnerability in these animals even before amyloid deposition.

Strain dependence of receptor regulation on chemical preconditioning in mice hippocampus

While one current focus for studying mechanisms of disease is investigation of transgenic mice confounding effects of the background strain often are neglected. We investigated mRNA expression of known markers of hypoxic tolerance by a semiquantitative RT-PCR (adenosine receptors (A1 and A3), nitric oxide synthases (eNOS and nNOS), APP production, progesterone receptor, and estrogen receptors alpha and beta) in CD-1, C3H, and B6 mice. We found differences in the baseline mRNA expression of adenosine A3 receptors in C3H mice and neuronal NOS in B6 mice as well as a distinct regulation of adenosine A3 receptors and estrogen receptor beta (no changes in C3H and B6 compared to upregulation in CD-1) on treatment of animals with a low dosage of 3-nitropropionate (20mg/kg body weight, i.p.). We conclude that the choice of background strain may confound interpretation of the effects of specific transgens in the study of the mechanisms of primary and induced hypoxic tolerance.

Ischemic preconditioning in the brain

PURPOSE OF REVIEW

Brain ischemia is responsible for significant morbidity and mortality associated with cardiovascular surgery, and is the end result of multiple disease states, including cardiac arrest, stroke, and traumatic brain injury. Despite significant resources dedicated to developing neuroprotective strategies, little progress has been made in this regard. Neuronal ischemic preconditioning is an endogenous neuroprotective strategy that provides sustained and robust ischemic tolerance. Identification of the mechanisms responsible for mediating the preconditioning response may offer novel therapeutic targets and further our understanding of the natural adaptations to brain injury.

RECENT FINDINGS

Recent research efforts have elucidated many intracellular signaling pathways that ultimately lead to ischemic tolerance after a preconditioning stimulus. Most of these are associated with glutamate receptor signal transduction, the intracellular kinases, and several transcription regulators. Microarray analysis has identified several gene families that warrant further investigation to identify novel candidates for neuroprotective therapies. These include genes involved in synaptic architecture and signal propagation, cell cycle and transcription regulators, and mediators of apoptosis such as the heat shock proteins and anti-apoptotic mitochondrial proteins.

SUMMARY

Neuronal ischemic preconditioning is an endogenous mechanism that leads to robust neuroprotection from ischemia. Identification of the upstream pathways that initiate preconditioning and candidate genes that mediate this phenomenon may offer novel therapeutic targets, with applicability to a variety of disease states and perioperative complications.