Nitric oxide averts hypoxia-induced damage during reoxygenation in rat heart

An Overview of NO Signaling Pathways in Aging

Nitric Oxide (NO) is a potent signaling molecule involved in the regulation of various cellular mechanisms and pathways under normal and pathological conditions. NO production, its effects, and its efficacy, are extremely sensitive to aging-related changes in the cells. Herein, we review the mechanisms of NO signaling in the cardiovascular system, central nervous system (CNS), reproduction system, as well as its effects on skin, kidneys, thyroid, muscles, and on the immune system during aging. The aging-related decline in NO levels and bioavailability is also discussed in this review. The decreased NO production by endothelial nitric oxide synthase (eNOS) was revealed in the aged cardiovascular system. In the CNS, the decline of the neuronal (n)NOS production of NO was related to the impairment of memory, sleep, and cognition. NO played an important role in the aging of oocytes and aged-induced erectile dysfunction. Aging downregulated NO signaling pathways in endothelial cells resulting in skin, kidney, thyroid, and muscle disorders. Putative therapeutic agents (natural/synthetic) affecting NO signaling mechanisms in the aging process are discussed in the present study. In summary, all of the studies reviewed demonstrate that NO plays a crucial role in the cellular aging processes.

Response of the Nitric Oxide System to Hypobaric Hypoxia in the Aged Striatum

BACKGROUND

Nitric oxide (NO) appears to play a key role in the hypoxic injury to the brain. We have previously reported that hypoxia/reoxygenation downregulated NO synthases (NOS) in the adult striatum. Until now, no data were available concerning the influence of aging in conjunction with hypoxia/reoxygenation on the NO system in the striatum.

OBJECTIVE

The aim of this study was to assess the role of the NO pathway in the hypoxic aged striatum.

METHODS

Wistar rats 24-25 months old were submitted to hypobaric hypoxia (20 min)/reoxygenation (0 h, 24 h, 5 days). Expression (PCR, immunohistochemistry/image analysis) and activity (NADPH-diaphorase/image analysis) of NOS isoforms (neuronal NOS or nNOS, endothelial NOS or eNOS, inducible NOS or iNOS) were analyzed together with nitrated protein expression (immunohistochemistry/image analysis). NO levels were indirectly quantified as nitrates/nitrites (NOx).

RESULTS

The mRNA levels of NOS isoforms were undetectable at 0 h after hypoxia in the striatum compared to the control. At later reoxygenation times, nNOS mRNA decreased, while eNOS mRNA augmented. Protein levels of nNOS and eNOS rose at 24 h after hypoxia, and iNOS protein increased at 5 days. NOx levels remained unchanged, whereas in situ NOS activity and protein nitration diminished during reoxygenation in the aged striatum.

CONCLUSION

The aged striatum may overexpress NOS isoforms as a neuroprotective-adaptive mechanism to hypoxia. However, this mechanism may not work properly in the aged striatum, since no changes in NO levels were detected after hypoxia. This may be related to the low activity of NOS isoforms in the hypoxic striatum.

HMGB1 induces apoptosis and EMT in association with increased autophagy following H/R injury in cardiomyocytes

Hypoxia/reoxygenation (H/R) is a critical factor in the pathogenesis of tissue injury following myocardial infarction (MI) which can lead to tissue damage and pathological remodeling. Therefore, it is necessary to try and prevent myocardial H/R injury in order to optimize the treatment of MI. This study aimed to explore the functions and molecular mechanisms of action of high mobility group box 1 (HMGB1) and its role in H/R injury to H9c2 cells. The mRNA expression of levels genes were detected by RT-qPCR. The protein levels were examined by western blot analysis. The Beclin 1 expression level was further determined by immunocytochemistry (ICC). In addition, an HMGB1 overexpression vector and a shRNA lentiviral vector were constructed in order to induce the overexpression and silencing of HMGB1, respectively. The apoptotic rate of the H9c2 cells was determined by flow cytometry. The expression of miR-210 was markedly increased following the exposure of the cells to H/R, thus indicating that the cell model of H/R injury was successfully established. In addition, an in vivo model of MI was also created using rats. The mRNA and protein level of HMGB1 was found to be upregulated in the myocardial tissue of the rats with MI and in the H9c2 cells subjected to H/R injury. HMGB1 promoted apoptosis by increasing the expression of cleaved caspase-3 and the apoptotic rate of the cells, while decreasing the expression of Bcl-2 during H/R in the H9c2 cells. HMGB1 promoted epithelial-to-mesenchymal transition (EMT) by reducing the protein level of the epithelial marker, E-cadherin, while increasing the expression of the mesenchymal markers, vimentin and fibroblast-specific protein (FSP), during H/R in the H9c2 cells. HMGB1 induced the apoptosis of the H9c2 cells and EMT following H/R in association with the induction of autophagy. HMGB1 induced autophagy by upregulating the expression of discoidin domain receptor 1 (DDR1) and downregulating the phosphorylation levels of mammalian target of rapamycin (mTOR). In conclusion, the findings of our study suggest that HMGB1 promotes apoptosis and EMT in association with the induction of autophagy through the upregulation of the expression of DDR1 and the downregulation of the phosphorylation of mTOR following H/R injury in H9c2 cells.

Differential hypoxic tolerance is mediated by activation of heat shock response and nitric oxide pathway

The fall in ambient oxygen pressure in high-altitude milieu elicits a wide range of physiological responses in the myocardium, which may differ from individual to individual. This condition, known as hypobaric hypoxia, invokes the cardioprotective heat shock response. The present study focuses on the role played by this ubiquitous response in mediating a differential tolerance to acute hypoxic stress. Sprague Dawley rats were exposed to simulated hypoxia equivalent to 223 mmHg pressure, screened on the basis of time taken for onset of a characteristic hyperventilatory response, and categorized as susceptible (<10 min), normal (10-25 min), or tolerant (>25 min). The tolerant animals displayed a significant upregulation of heat shock protein (Hsp)70/HSPA, evident through immunohistochemical staining of the cardiac tissue. The increased expression of transcription factor heat shock factor-1 led to the downstream activation of other chaperones, including Hsp90/HSPC, Hsp60/HSPD1, and Hsp27/HSPB1. The higher induction of HSPs in tolerant animals contributed to higher nitric oxide synthesis mediated by both endothelial nitric oxide synthase and inducible nitric oxide synthase activation. Conversely, susceptible animals showed significantly higher expression of the proinflammatory markers tumor necrosis factor alpha and nuclear factor kappa-light-chain enhancer of activated B cells in the myocardium. Evaluation of circulatory stress markers identified increased levels of reactive oxygen species, corticosterone and endothelin-1 in the susceptible animals highlighting their vulnerability to hypoxic stress. The heat shock response, through the action of chaperones and enhanced NO generation thus contributes substantially to the ability to sustain survival under acute sub lethal hypoxia.

Renal PKC-ε deficiency attenuates acute kidney injury and ischemic allograft injury via TNF-α-dependent inhibition of apoptosis and inflammation

Acute kidney injury (AKI) increases the risk of morbidity and mortality after major surgery and transplantation. We investigated the effect of PKC-ε deficiency on AKI and ischemic allograft damage after kidney transplantation. PKC-ε-deficient and wild type (WT) control mice were subjected to 35 min of renal pedicle clamping to induce AKI. PKC-ε deficiency was associated with a marked improvement in survival and an attenuated loss of kidney function. Furthermore, functional MRI experiments revealed better renal perfusion in PKC-ε-deficient mice than in WT mice one day after IRI. Acute tubular necrosis and neutrophil infiltration were markedly reduced in PKC-ε-deficient mice. To determine whether this resistance to ischemia-reperfusion injury resulted from changes in local renal cells or infiltrating leukocytes, we studied a life-supporting renal transplant model of ischemic graft injury. We transplanted kidneys from H2b PKC-ε-deficient mice (129/SV) and their corresponding WT littermates into major histocompatibility complex-incompatible H2d recipients (BALB/c) and induced ischemic graft injury by prolonged cold ischemia time. Recipients of WT allografts developed severe renal failure and died within 10 days of transplantation. Recipients of PKC-ε-deficient allografts had better renal function and survival; they had less generation of ROS and upregulation of proinflammatory proteins (i.e., ICAM-1, inducible nitric oxide synthase, and TNF-α) and showed less tubular epithelial cell apoptosis and inflammation in their allografts. These data suggest that local renal PKC-ε expression mediates proapoptotic and proinflammatory signaling and that an inhibitor of PKC-ε signaling could be used to prevent hypoxia-induced AKI.