Phosphorylation of neuronal nitric oxide synthase at Ser1412 in the dentate gyrus of rat brain after transient forebrain ischemia

Mucopolysaccharide polysulfate increases local skin blood volume through nitric oxide production

BACKGROUND

Mucopolysaccharide polysulfate (MPS) is widely used as an active ingredient in topical preparations for the treatment of asteatosis and blood flow disorders. Although topical MPS products can increase cutaneous blood flow (CBF), the underlying mechanism remains unclear.

OBJECTIVE

In this study, we aimed to elucidate how MPS increases CBF. We investigated the association of nitric oxide (NO), a powerful mediator associated with increased local blood volume, with the blood flow-accelerating action of MPS in mice. In addition, we verified the effects of MPS on NO production in different skin cell types, such as keratinocytes (KCs), endothelial cells (ECs), and dermal fibroblasts (DFs).

METHODS

We used raster-scanning optoacoustic imaging mesoscopy to observe in vivo changes in the skin blood volume. NO production was determined in each cell using an NO indicator. An enzyme-linked immunoassay was used to measure the phosphorylated nitric oxide synthase (NOS) levels in ECs, DFs, and KCs in the presence or absence of MPS.

RESULTS

Topical application of MPS increased the skin blood volume in mice, and this increase was abolished through the addition of NOS inhibitors. MPS promoted the dose-dependent production of NO in various cells, which caused alterations in the phosphorylation state of NOS.

CONCLUSION

Our findings demonstrate that MPS promotes an increase in skin blood volume and NO production in various skin cell types. These results suggest that MPS can potentially accelerate CBF through the NO biosynthesis pathway in different skin cell types.

Differential superoxide production in phosphorylated neuronal nitric oxide synthase mu and alpha variants

Neuronal nitric oxide synthase (nNOS) is regulated by phosphorylation in vivo, yet the underlying biochemical mechanisms remain unclear, primarily due to difficulty in obtaining milligram quantities of phosphorylated nNOS protein; detailed spectroscopic and rapid kinetics investigations require purified protein samples at a concentration in the range of hundreds microM. Moreover, the functional diversity of the nNOS isoform is linked to its splice variants. Also of note is that determination of protein phosphorylation stoichiometry remains as a challenge. To address these issues, this study first expanded a recent genetic code expansion approach to produce phosphorylated rat nNOSμ and nNOSα holoproteins through site-specific incorporation of phosphoserine (pSer) at residues 1446 and 1412, respectively; this site is at the C-terminal tail region, a NOS-unique regulatory element. A quantitative mass spectrometric approach was then developed in-house to analyze unphosphorylated peptides in phosphatase-treated and -untreated phospho-nNOS proteins. The observed pSer-incorporation efficiency consistently exceeded 80%, showing high pSer-incorporation efficiency. Notably, EPR spin trapping results demonstrate that under l-arginine-depleted conditions, pSer1412 nNOSα presented a significant reduction in superoxide generation, whereas pSer1446 nNOSμ exhibited the opposite effect, compared to their unphosphorylated counterparts. This suggests that phosphorylation at the C-terminal tail has a regulatory effect on nNOS uncoupling that may differ between variant forms. Furthermore, the methodologies for incorporating pSer into large, complex protein and quantifying the percentage of phosphorylation in recombinant purified protein should be applicable to other protein systems.

CaMKIIα as a Promising Drug Target for Ischemic Grey Matter

Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) is a major mediator of Ca²⁺-dependent signaling pathways in various cell types throughout the body. Its neuronal isoform CaMKIIα (alpha) centrally integrates physiological but also pathological glutamate signals directly downstream of glutamate receptors and has thus emerged as a target for ischemic stroke. Previous studies provided evidence for the involvement of CaMKII activity in ischemic cell death by showing that CaMKII inhibition affords substantial neuroprotection. However, broad inhibition of this central kinase is challenging because various essential physiological processes like synaptic plasticity rely on intact CaMKII regulation. Thus, specific strategies for targeting CaMKII after ischemia are warranted which would ideally only interfere with pathological activity of CaMKII. This review highlights recent advances in the understanding of how ischemia affects CaMKII and how pathospecific pharmacological targeting of CaMKII signaling could be achieved. Specifically, we discuss direct targeting of CaMKII kinase activity with peptide inhibitors versus indirect targeting of the association (hub) domain of CaMKIIα with analogues of γ-hydroxybutyrate (GHB) as a potential way to achieve more specific pharmacological modulation of CaMKII activity after ischemia.

Role of the macula densa sodium glucose cotransporter type 1-neuronal nitric oxide synthase-tubuloglomerular feedback pathway in diabetic hyperfiltration

An increase of glomerular filtration rate (GFR) is a common observation in early diabetes and is considered a key risk factor for subsequent kidney injury. However, the mechanisms underlying diabetic hyperfiltration have not been fully clarified. Here, we tested the hypothesis that macula densa neuronal nitric oxide synthase (NOS1) is upregulated via sodium glucose cotransporter type 1 (SGLT1) in diabetes, which then inhibits tubuloglomerular feedback (TGF) promoting glomerular hyperfiltration. Therefore, we examined changes in cortical NOS1 expression and phosphorylation, nitric oxide production in the macula densa, TGF response, and GFR during the early stage of insulin-deficient (Akita) diabetes in wild-type and macula densa-specific NOS1 knockout mice. A set of sophisticated techniques including microperfusion of juxtaglomerular apparatus in vitro, micropuncture of kidney tubules in vivo, and clearance kinetics of plasma fluorescent-sinistrin were employed. Complementary studies tested the role of SGLT1 in SGLT1 knockout mice and explored NOS1 expression and phosphorylation in kidney biopsies of cadaveric donors. Diabetic mice had upregulated macula densa NOS1, inhibited TGF and elevated GFR. Macula densa-selective NOS1 knockout attenuated the diabetes-induced TGF inhibition and GFR elevation. Additionally, deletion of SGLT1 prevented the upregulation of macula densa NOS1 and attenuated inhibition of TGF in diabetic mice. Furthermore, the expression and phosphorylation levels of NOS1 were increased in cadaveric kidneys of diabetics and positively correlated with blood glucose as well as estimated GFR in the donors. Thus, our findings demonstrate that the macula densa SGLT1-NOS1-TGF pathway plays a crucial role in the control of GFR in diabetes.

Serine/Threonine Phosphatases in LTP: Two B or Not to Be the Protein Synthesis Blocker-Induced Impairment of Early Phase

Dephosphorylation of target proteins at serine/threonine residues is one of the most crucial mechanisms regulating their activity and, consequently, the cellular functions. The role of phosphatases in synaptic plasticity, especially in long-term depression or depotentiation, has been reported. We studied serine/threonine phosphatase activity during the protein synthesis blocker (PSB)-induced impairment of long-term potentiation (LTP). Established protein phosphatase 2B (PP2B, calcineurin) inhibitor cyclosporin A prevented the LTP early phase (E-LTP) decline produced by pretreatment of hippocampal slices with cycloheximide or anisomycin. For the first time, we directly measured serine/threonine phosphatase activity during E-LTP, and its significant increase in PSB-treated slices was demonstrated. Nitric oxide (NO) donor SNAP also heightened phosphatase activity in the same manner as PSB, and simultaneous application of anisomycin + SNAP had no synergistic effect. Direct measurement of the NO production in hippocampal slices by the NO-specific fluorescent probe DAF-FM revealed that PSBs strongly stimulate the NO concentration in all studied brain areas: CA1, CA3, and dentate gyrus (DG). Cyclosporin A fully abolished the PSB-induced NO production in the hippocampus, suggesting a close relationship between nNOS and PP2B activity. Surprisingly, cyclosporin A alone impaired short-term plasticity in CA1 by decreasing paired-pulse facilitation, which suggests bi-directionality of the influences of PP2B in the hippocampus. In conclusion, we proposed a minimal model of signaling events that occur during LTP induction in normal conditions and the PSB-treated slices.

Effects of inosine monophosphate and exercise training on neuronal nitric oxide synthase in the mouse brain

Recently, the purine nucleoside inosine has been demonstrated to have several neuroprotective effects. Similarly, exercise training has well-known beneficial effects on mental health and cognitive function. Neuronal nitric oxide synthase (nNOS) is a key neuronal messenger in several brain regions, and the downregulation of nNOS has been shown to improve brain function. However, whether inosine and exercise training have combined effects on nNOS pathway-related proteins in the brain remains unknown. We found, for the first time, that inosine monophosphate (IMP), which is a precursor of inosine, decreases nNOS levels in the ventral hippocampus (vHp) and the cerebellum (Ce), but not in the dorsal hippocampus (dHp). In the vHp, the phosphorylation of cAMP response element-binding protein (CREB) was also upregulated, which negatively correlated with nNOS protein levels. In the cerebral cortex (Cx), no significant activation of the nNOS pathway was observed. In the dHp, vHp, Cx, and Ce, no interactions between the effects of IMP and exercise on nNOS protein and CREB phosphorylation levels were observed. The phosphorylation of nNOS was regulated by the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) pathway. Although IMP induced minor changes in Akt phosphorylation, nNOS phosphorylation was unchanged by either IMP or exercise. In conclusion, in the vHp, which is associated with emotional behavior, IMP decreased nNOS levels and activated CREB, suggesting that IMP can elicit anxiolytic effects.

Anxiety-like behaviors and hippocampal nNOS in response to diet-induced obesity combined with exercise

A high-fat diet (HFD) and overweight status can induce hippocampal dysfunction, leading to depression and anxiety. Exercise has beneficial effects on emotional behaviors. We previously reported that exercise training rescues HFD-induced excess hippocampal neuronal nitric oxide synthase (nNOS) expression, which is a key regulator of anxiety. Here, we investigated anxiety-like behaviors and hippocampal nNOS expression in response to HFD combined with exercise. Mice were assigned to standard diet, HFD, or HFD with exercise groups for 12 weeks. We found that exercise during the final 6 weeks of the HFD regime improved 12 weeks of HFD-induced defecation, accompanied by rescue of excess nNOS expression. However, anxiety indicators in the elevated plus maze were unchanged. These effects were not apparent after only 1 week of exercise. In conclusion, 6 weeks of exercise training reduced HFD-related anxiety according to one of our measures (defecation), and reversed changes in the hippocampal nNOS/NO pathway.

Generation and characterization of functional phosphoserine-incorporated neuronal nitric oxide synthase holoenzyme

Phosphorylation is an important pathway for the regulation of nitric oxide synthase (NOS) at the posttranslational level. However, the molecular underpinnings of NOS regulation by phosphorylations remain unclear to date, mainly because of the problems in making a good amount of active phospho-NOS proteins. Herein, we have established a system in which recombinant rat nNOS holoprotein can be produced with site-specific incorporation of phosphoserine (pSer) at residue 1412, using a specialized bacterial host strain for pSer incorporation. The pSer1412 nNOS protein demonstrates UV-Vis, far-UV CD and fluorescence spectral properties that are identical to those of nNOS overexpressed in other bacterial strains. The protein is also functional, possessing normal NO production and NADPH oxidation activities in the presence of abundant substrate L-Arg. Conversely, the rate of FMN-heme interdomain electron transfer (IET) in pSer1412 nNOS is considerably lower than that of wild-type (wt) nNOS, while the phosphomimetic S1142E mutant possesses similar electron transfer kinetics to that of wt. The successful incorporation and high yield of pSer1412 into rat nNOS and the significant change in the IET kinetics upon the phosphorylation demonstrate a highly useful method for incorporating native phosphorylation sites as a substantial improvement to commonly used phosphomimetics.

Thyroid hormones affect nitrergic innervation function in rat mesenteric artery: Role of the PI3K/AKT pathway

We aimed to determine the influence of nitrergic innervation function on the decreased mesenteric arterial tone induced by high levels of triiodothyronine (T3), as a model of acute thyroiditis, as well as the mechanism/s implicated. We analysed in mesenteric segments from male Wistar rats the effect of 10 nmol/L T3 (2 h) on the vasomotor response to electrical field stimulation (EFS) in the presence/absence of specific neuronal NOS (nNOS) inhibitor L-NPA, or superoxide anion scavenger tempol. Nitric oxide (NO) release was measured in the presence/absence of tempol or PI3K inhibitor LY294002. Superoxide anion and peroxynitrite releases, nNOS, PI3K, AKT and superoxide dismutase (SOD) 1 and 2 expressions, nNOS and AKT phosphorylation, and SOD activity were analysed. T3 decreased EFS-induced vasoconstriction. L-NPA increased EFS-induced vasoconstriction more markedly in T3-incubated segments. T3 increased NO release. Tempol decreased EFS-induced vasoconstriction and augmented NO release only in segments without T3. LY294002 decreased NO release in T3-incubated segments. T3 diminished superoxide anion and peroxynitrite formation, enhanced SOD-2 expression, nNOS and AKT phosphorylations and SOD activity, and did not modify nNOS, PI3K, AKT and SOD-1 expressions. In conclusion, these results show a compensatory mechanism aimed at reducing the enhanced blood pressure that appears during acute thyroiditis.

Calmodulin-induced Conformational Control and Allostery Underlying Neuronal Nitric Oxide Synthase Activation

Nitric oxide synthase (NOS) is the primary generator of nitric oxide signals controlling diverse physiological processes such as neurotransmission and vasodilation. NOS activation is contingent on Ca²⁺/calmodulin binding at a linker between its oxygenase and reductase domains to induce large conformational changes that orchestrate inter-domain electron transfer. However, the structural dynamics underlying activation of full-length NOS remain ambiguous. Employing hydrogen-deuterium exchange mass spectrometry, we reveal mechanisms underlying neuronal NOS activation by calmodulin and regulation by phosphorylation. We demonstrate that calmodulin binding orders the junction between reductase and oxygenase domains, exposes the FMN subdomain, and elicits a more dynamic oxygenase active site. Furthermore, we demonstrate that phosphorylation partially mimics calmodulin activation to modulate neuronal NOS activity via long-range allostery. Calmodulin binding and phosphorylation ultimately promote a more dynamic holoenzyme while coordinating inter-domain communication and electron transfer.

Modulation of nNOSser852 phosphorylation and translocation by PKA/PP1 pathway in endothelial cells

Neuronal nitric oxide synthase (nNOS) is now considered an important player in vascular function. It has a protective role in atherosclerosis and hypertension. However, despite its importance, little is known about the mechanisms that regulate its activity in vascular cells. Here we explore the mechanisms by which nNOS is activated in endothelium. We evaluated aorta relaxation response and phosphorylation of nNOS during protein phosphatases 1 and 2 (PP1 and PP2) inhibition, in eNOS silenced mice. PP1 translocation and interaction between the nuclear inhibitor of PP1 (NIPP1) and PP1 was evaluated in endothelial EA.hy926 cells. We demonstrate here that acetylcholine (Ach)-induced relaxation is completely abolished by nNOS inhibition in eNOS silenced mice aorta which also decreased NO and H₂O₂ concentrations. ACh induced dephosphorylation of nNOS^ser852 in aorta after 20 min stimulation. Endothelial cells also showed a decrease in nNOS^ser852 phosphorylation during 20 min of ACh stimulation. PP2 inhibition had no effect on Ach-induced nNOS^Ser852 dephosphorylation in endothelial cells and did not modify Ach-induced vasodilation in aorta from eNOS silenced mice. Non-selective PP1/PP2 inhibition prevented nNOSSer852 dephosphorylation in endothelial cells and prevented Ach-induced vasodilation in eNOS silenced mice. ACh induced time-dependent PP1 and NIPP1 dissociation and PP1 translocation to cytoplasm. Protein kinase A (PKA) inhibition abolished PP1 translocation and further nNOS^ser852 dephosphorylation. In addition, 8-Br-cAMP reduced NIPP1/PP1 interaction, stimulated PP1 translocation and nNOS^ser852 dephosphorylation. Moreover, PKA Inhibition led to a decreased nNOS translocation to perinuclear region. Taken together, our results elucidate a mechanism whereby PP1 is activated by a cAMP/PKA-dependent pathway, leading to dephosphorylation of nNOS^ser852 and subsequent NO and possible H₂O₂ production resulting in endothelium-dependent vascular relaxation.

The protective effects of propofol against CoCl2-induced HT22 cell hypoxia injury via PP2A/CAMKIIα/nNOS pathway

Background

Perioperative cerebral ischemia/hypoxia could induce hippocampal injury and has been reported to induce cognitive impairment. In this study, we used cobalt chloride (CoCl₂) to build a hypoxia model in mouse hippocampal cell lines. Propofol, a widely used intravenous anesthetic agent, has been demonstrated to have neuroprotective effect. Here, we explored whether and how propofol attenuated CoCl₂-induced mouse hippocampal HT22 cell injury.

Methods

Mouse hippocampal HT22 cells were pretreated with propofol, and then stimulated with CoCl₂. Cell viability was measured by cell counting kit 8 (CCK8). The effect of propofol on CoCl₂-modulated expressions of B-cell lymphoma 2 (Bcl-2), BAX, cleaved caspase 3, phosphatase A2 (PP2A), and the phosphorylation of Ca²⁺/Calmodulin (CaM)-dependent protein kinase II (pCAMKIIα), neuron nitric oxide synthase at Ser¹⁴¹² (pnNOS-Ser¹⁴¹²), neuron nitric oxide synthase at Ser⁸⁴⁷ (pnNOS-Ser⁸⁴⁷) were detected by Western blot analysis.

Results

Compared with control, CoCl₂ treatment could significantly decrease cell viability, which could be reversed by propofol. Further, we found CoCl₂ treatment could up-regulate the expression of PP2A, BAX, cleaved caspase three and cause the phosphorylation of nNOS-Ser¹⁴¹², but it down-regulated the expression of Bcl-2 and the phosphorylation of CAMKIIα and nNOS-Ser⁸⁴⁷. More importantly, these CoCl₂-mediated effects were attentuated by propofol. In addition, we demonstrated that propofol could exert similar effect to that of the PP2A inhibitor (okadaic acid). Further, the PP2A activator (FTY720) and the CAMKIIα inhibitor (KN93) could reverse the neuroprotective effect of propofol.

Conclusion

Our data indicated that propofol could attenuate CoCl₂-induced HT22 cells hypoxia injury via PP2A/CAMKIIα/nNOS pathway.

The Expression of NP847 and Sox2 after TBI and Its Influence on NSCs

The proliferation and differentiation of neural stem cells (NSCs) is important for neural regeneration after cerebral injury. Here, for the first time, we show that phosphorylated (p)-ser847-nNOS (NP847), rather than nNOS, may play a major role in NSC proliferation after traumatic brain injury (TBI). Western blot results demonstrated that the expression of NP847 and Sox2 in the hippocampus is up-regulated after TBI, and they both peak 3 days after brain injury. In addition, an immunofluorescence experiment indicated that NP847 and Sox2 partly co-localize in the nuclei of NSCs after TBI. Further immunoprecipitation experiments found that NP847 and Sox2 can directly interact with each other in NSCs. Moreover, in an OGD model of NSCs, NP847 expression is decreased, which is followed by the down-regulation of Sox2. Interestingly, in this study, we did not observe changes in the expression of nNOS in the OGD model. Further research data suggest that the NP847-Sox2 complex may play a major role in NSCs through the Shh/Gli signaling pathway in a CaMKII-dependent manner after brain injury.