Spring brings breezes, wheezes, and pollen oxidases.

While the release of pollen into the air is essential for the reproduction of plants, the accidental yet inevitable uptake of pollen into human airways can cause symptoms of seasonal allergies and asthma. The symptomatic response to pollen is caused by granulocytes that produce inflammation, which is due in part to oxidative stress through the action of NADPH oxidases. The recruitment of these inflammatory granulocytes was previously thought to depend entirely on the activation of an adaptive immune response. In this issue of the JCI, Boldogh et al. demonstrate that pollens contain endogenous NADPH oxidase activity, which functions to generate local "danger signals" in nearby airway epithelium. These signals in turn trigger the early recruitment of granulocytes, even in the absence of the adaptive immune response. These findings suggest that inhibition of the pollen oxidase may provide a way to antagonize allergic inflammation at a very early step.

Nox regulation of smooth muscle contraction.

The catalytic subunit gp91phox (Nox2) of the NADPH oxidase of mammalian phagocytes is activated by microbes and immune mediators to produce large amounts of reactive oxygen species (ROS) which participate in microbial killing. Homologs of gp91phox, the Nox and Duox enzymes, were recently described in a range of organisms, including plants, vertebrates, and invertebrates such as Drosophila melanogaster. While their enzymology and cell biology are being extensively studied in many laboratories, little is known about in vivo functions of Noxes. Here, we establish and use an inducible system for RNAi to discover functions of dNox, an ortholog of human Nox5 in Drosophila. We report here that depletion of dNox in musculature causes retention of mature eggs within ovaries, leading to female sterility. In dNox-depleted ovaries and ovaries treated with a Nox inhibitor, muscular contractions induced by the neuropeptide proctolin are markedly inhibited. This functional defect results from a requirement for dNox-for the proctolin-induced calcium flux in Drosophila ovaries. Thus, these studies demonstrate a novel biological role for Nox-generated ROS in mediating agonist-induced calcium flux and smooth muscle contraction.

The use of model systems to study biological functions of Nox/Duox enzymes.

ROS (reactive oxygen species; including superoxide and H202) are conventionally thought of as being broadly reactive and cytotoxic. Phagocytes utilize an NADPH oxidase to generate large amounts of ROS, and exploit their toxic properties as a host-defence mechanism to kill invading microbes. However, the recent discovery of the Nox and Duox enzymes that are expressed in many non-phagocytic cells implies that the 'deliberate' generation of ROS has additional cellular roles, which are currently incompletely understood. Functions of ROS in mammals have been inferred primarily from cell-culture experiments, and include signalling for mitogenic growth, apoptosis and angiogenesis. Nox/Duox enzymes may also provide H202 as a substrate for peroxidase enzymes (or, in the case of Duox, for its own peroxidase domain), thereby supporting peroxidative reactions. A broad comparison of biological functions of ROS and Nox enzymes across species and kingdoms provides insights into possible functions in mammals. To further understand novel biological roles for Nox/Duox enzymes, we are manipulating the expression of Nox/Duox enzymes in model organisms including Caenorhabditis elegans, Drosophila melanogaster and mouse. This chapter focuses on new insights into the roles of Nox enzymes gained from these approaches.