bims-noxint Biomed News
on NADPH oxidases in tumorigenesis
Issue of 2020‒12‒06
six papers selected by
Laia Caja Puigsubira
Uppsala University

  1. Arterioscler Thromb Vasc Biol. 2020 Dec 03. ATVBAHA120315565
      OBJECTIVE: Using 3KO (triple NOX [NADPH oxidase] knockout) mice (ie, NOX1-/-/NOX2-/-/NOX4-/-), we aimed to clarify the role of this family of enzymes in the regulation of platelets in vitro and hemostasis in vivo. Approach and Results: 3KO mice displayed significantly reduced platelet superoxide radical generation, which was associated with impaired platelet aggregation, adhesion, and thrombus formation in response to the key agonists collagen and thrombin. A comparison with single-gene knockouts suggested that the phenotype of 3KO platelets is the combination of the effects of the genetic deletion of NOX1 and NOX2, while NOX4 does not show any significant function in platelet regulation. 3KO platelets displayed significantly higher levels of cGMP-a negative platelet regulator that activates PKG (protein kinase G). The inhibition of PKG substantially but only partially rescued the defective phenotype of 3KO platelets, which are responsive to both collagen and thrombin in the presence of the PKG inhibitors KT5823 or Rp-8-pCPT-cGMPs, but not in the presence of the NOS (NO synthase) inhibitor L-NG-monomethyl arginine. In vivo, triple NOX deficiency protected against ferric chloride-driven carotid artery thrombosis and experimental pulmonary embolism, while hemostasis tested in a tail-tip transection assay was not affected. Procoagulatory activity of platelets (ie, phosphatidylserine surface exposure) and the coagulation cascade in platelet-free plasma were normal.CONCLUSIONS: This study indicates that inhibiting NOXs has strong antithrombotic effects partially caused by increased intracellular cGMP but spares hemostasis. NOXs are, therefore, pharmacotherapeutic targets to develop new antithrombotic drugs without bleeding side effects.
    Keywords:  NADPH oxidases; blood platelets; chlorides; oxidation-reduction; thrombosis
  2. Free Radic Biol Med. 2020 Nov 26. pii: S0891-5849(20)31636-1. [Epub ahead of print]
      Modern lifestyles, including lack of physical activity and poor nutritional habits, are driving the rapidly increasing prevalence of obesity and type 2 diabetes. Increased levels of free fatty acids (FFAs), particularly saturated FFAs, in obese individuals have been linked to pancreatic β-cell failure. This process, termed lipotoxicity, involves activation of several stress responses, including ER stress and oxidative stress. However, the molecular underpinnings and causal relationships between the disparate stress responses remain unclear. Here we employed transgenic mice, expressing a genetically-encoded cytosolic H2O2 sensor, roGFP2-Orp1, to monitor dynamic changes in H2O2 levels in pancreatic islets in response to chronic palmitate exposure. We identified a transient increase in H2O2 levels from 4-8 hours after palmitate addition, which was mirrored by a concomitant decrease in cellular NAD(P)H levels. Intriguingly, islets isolated from NOX2 knock-out mice displayed no H2O2 transient upon chronic palmitate treatment. Furthermore, NOX2 knockout rescued palmitate-dependent impairment of insulin secretion, calcium homeostasis and viability. Chemical inhibition of NOX activity protected islets from palmitate-induced impairment in insulin secretion, however had no detectable impact upon the induction of ER stress. In summary, our results reveal that transient NOX2-dependent H2O2 production is a likely cause of early palmitate-dependent lipotoxic effects.
    Keywords:  ER stress; NADPH oxidase; Palmitate; lipotoxicity; β-cell
  3. Biochem Biophys Res Commun. 2020 Dec 01. pii: S0006-291X(20)32081-7. [Epub ahead of print]
      Diabetic nephropathy (DN) endangers health and is a high financial public burden worldwide. Risk of DN is positively correlated with high levels of reactive oxygen species (ROS). Carnosine, an antioxidant, actively regulates cell function and has the potential to reduce the occurrence of DN. Here, we explored whether carnosine could prevent oxidative stress in human kidney tubular epithelial (HK2) cells and, if so, the mechanisms underlying this effect. HK2 cells were cultured with the ROS hydrogen peroxide (H2O2) for 24 h and then treated with carnosine. In H2O2-damaged HK2 cells, carnosine significantly increased cell viability, assessed using a Cell Counting Kit 8, increased total superoxide dismutase (T-SOD) activity, assessed using a T-SOD activity detection kit, but decreased ROS levels, assessed using a ROS-sensitive fluorescent probe. Western blotting analyses to determine the protein expression levels of BAX, BCL-2, caspase 3, and the NADPH oxidase isoforms NOX2 and NOX4, as well as confocal laser scanning microscopy to assess changes in the mitochondrial membrane potential and the relative position of mitochondria to cytochrome c, indicated that carnosine inhibited apoptosis via the mitochondrial pathway in H2O2-damaged HK2 cells. Significantly decreased NOX4 expression and increased T-SOD activity in the presence of carnosine reduced the production of intracellular ROS, relieving oxidative stress to inhibit apoptosis via the mitochondrial pathway. These findings provide molecular mechanistic insights underlying the effects of carnosine, particularly as a potential therapeutic in DN.
    Keywords:  Carnosine; HK2 cells; Mitochondrial pathway of apoptosis; Oxidative stress
  4. Metabolites. 2020 Nov 24. pii: E480. [Epub ahead of print]10(12):
      Compelling evidence from earlier studies suggests that the pancreatic beta cell is inherently weak in its antioxidant defense mechanisms to face the burden of protecting itself against the increased intracellular oxidative stress following exposure to proinflammatory cytokines. Recent evidence implicates novel roles for nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (Noxs) as contributors to the excessive intracellular oxidative stress and damage under metabolic stress conditions. This review highlights the existing evidence on the regulatory roles of at least three forms of Noxs, namely Nox1, Nox2, and Nox4, in the cascade of events leading to islet beta cell dysfunction, specifically under the duress of chronic exposure to cytokines. Potential crosstalk between key signaling pathways (e.g., inducible nitric oxide synthase [iNOS] and Noxs) in the generation and propagation of reactive molecules and metabolites leading to mitochondrial damage and cell apoptosis is discussed. Available data accrued in investigations involving small-molecule inhibitors and antioxidant protein expression methods as tools toward the prevention of cytokine-induced oxidative damage are reviewed. Lastly, current knowledge gaps in this field, and possible avenues for future research are highlighted.
    Keywords:  NADPH oxidases; Rac1; diabetes; oxidative stress; pancreatic beta cell; proinflammatory cytokines
  5. Cell Stem Cell. 2020 Nov 25. pii: S1934-5909(20)30538-5. [Epub ahead of print]
      Cellular redox states regulate the balance between stem cell maintenance and activation. Increased levels of intracellular reactive oxygen species (ROS) are linked to proliferation and lineage specification. In contrast to this general principle, we here show that in the hippocampus of adult mice, quiescent neural precursor cells (NPCs) maintain the highest ROS levels (hiROS). Classifying NPCs on the basis of cellular ROS content identified distinct functional states. Shifts in ROS content primed cells for a subsequent state transition, with lower ROS content marking proliferative activity and differentiation. Physical activity, a physiological activator of adult hippocampal neurogenesis, recruited hiROS NPCs into proliferation via a transient Nox2-dependent ROS surge. In the absence of Nox2, baseline neurogenesis was unaffected, but the activity-induced increase in proliferation disappeared. These results provide a metabolic classification of NPC functional states and describe a mechanism linking the modulation of cellular ROS by behavioral cues to the activation of adult NPCs.
    Keywords:  adult neurogenesis; adult stem cells; physical activity; quiescent neural stem cells; reactive oxygen species; stem cell heterogeneity
  6. Sci Rep. 2020 Dec 03. 10(1): 21018
      Hepatic fibrogenesis is characterized by activation of hepatic stellate cells (HSCs) and accumulation of extracellular matrix (ECM). The impact of ECM on TGF-β-mediated fibrogenic signaling pathway in HSCs has remained obscure. We studied the role of non-receptor tyrosine kinase focal adhesion kinase (FAK) family members in TGF-β-signaling in HSCs. We used a CCl4-induced liver fibrosis mice model to evaluate the effect of FAK family kinase inhibitors on liver fibrosis. RT-PCR and Western blot were used to measure the expression of its target genes; α-SMA, collagen, Nox4, TGF-β1, Smad7, and CTGF. Pharmacological inhibitors, siRNA-mediated knock-down, and plasmid-based overexpression were adopted to modulate the function and the expression level of proteins. Association of PYK2 activation with liver fibrosis was confirmed in liver samples from CCl4-treated mice and patients with significant fibrosis or cirrhosis. TGF-β treatment up-regulated expression of α-SMA, type I collagen, NOX4, CTGF, TGF-β1, and Smad7 in LX-2 cells. Inhibition of FAK family members suppressed TGF-β-mediated fibrogenic signaling. SiRNA experiments demonstrated that TGF-β1 and Smad7 were upregulated via Smad-dependent pathway through FAK activation. In addition, CTGF induction was Smad-independent and PYK2-dependent. Furthermore, RhoA activation was essential for TGF-β-mediated CTGF induction, evidenced by using ROCK inhibitor and dominant negative RhoA expression. We identified that TGF-β1-induced activation of PYK2-Src-RhoA triad leads to YAP/TAZ activation for CTGF induction in liver fibrosis. These findings provide new insights into the role of focal adhesion molecules in liver fibrogenesis, and targeting PYK2 may be an attractive target for developing novel therapeutic strategies for the treatment of liver fibrosis.