The dual role of heme oxygenase in regulating apoptosis in the nervous system of Drosophila melanogaster

Evolutionary formation of melatonin and vitamin D in early life forms: insects take centre stage

Melatonin, a product of tryptophan metabolism via serotonin, is a molecule with an indole backbone that is widely produced by bacteria, unicellular eukaryotic organisms, plants, fungi and all animal taxa. Aside from its role in the regulation of circadian rhythms, it has diverse biological actions including regulation of cytoprotective responses and other functions crucial for survival across different species. The latter properties are also shared by its metabolites including kynuric products generated by reactive oxygen species or phototransfomation induced by ultraviolet radiation. Vitamins D and related photoproducts originate from phototransformation of ∆5,7 sterols, of which 7-dehydrocholesterol and ergosterol are examples. Their ∆5,7 bonds in the B ring absorb solar ultraviolet radiation [290-315 nm, ultraviolet B (UVB) radiation] resulting in B ring opening to produce previtamin D, also referred to as a secosteroid. Once formed, previtamin D can either undergo thermal-induced isomerization to vitamin D or absorb UVB radiation to be transformed into photoproducts including lumisterol and tachysterol. Vitamin D, as well as the previtamin D photoproducts lumisterol and tachysterol, are hydroxylated by cyochrome P450 (CYP) enzymes to produce biologically active hydroxyderivatives. The best known of these is 1,25-dihydroxyvitamin D (1,25(OH)2D) for which the major function in vertebrates is regulation of calcium and phosphorus metabolism. Herein we review data on melatonin production and metabolism and discuss their functions in insects. We discuss production of previtamin D and vitamin D, and their photoproducts in fungi, plants and insects, as well as mechanisms for their enzymatic activation and suggest possible biological functions for them in these groups of organisms. For the detection of these secosteroids and their precursors and photoderivatives, as well as melatonin metabolites, we focus on honey produced by bees and on body extracts of Drosophila melanogaster. Common biological functions for melatonin derivatives and secosteroids such as cytoprotective and photoprotective actions in insects are discussed. We provide hypotheses for the photoproduction of other secosteroids and of kynuric metabolites of melatonin, based on the known photobiology of ∆5,7 sterols and of the indole ring, respectively. We also offer possible mechanisms of actions for these unique molecules and summarise differences and similarities of melatoninergic and secosteroidogenic pathways in diverse organisms including insects.

Reduced iron and cobalt levels in response to curcumin supplementation are not responsible for the prolonged larval development and do not affect the oxidative stress tolerance and polyamine status of D. melanogaster

Recent reports indicated that the phytochemical curcumin possesses iron-chelating activity. Here, by employing the fruit fly Drosophila melanogaster, we conducted feeding studies supplementing curcumin or, as a control, the iron chelator bathophenanthroline (BPA). First, the absorption and further metabolization of dietary curcuminoids were proved by metabolomics analyses. Next, we found that 0.2% dietary curcumin, similar to BPA, lowered the iron but also the cobalt content, and to a lesser extent affected the manganese and zinc status. Supplementation during larval stages was required and sufficient for both compounds to elicit these alterations in adult animals. However, curcumin-induced retarded larval development was not attributable to the changed trace metal status. In addition, a reduction in the iron content of up to 70% by curcumin or BPA supplementation did not reduce heme-dependent catalase activity and tolerance toward H2 O2 in D. melanogaster. Moreover, polyamines were not influenced by curcumin treatment and decreased iron levels. This was confirmed for selected organs from 0.2% curcumin-treated mice, except for the spleen. Here, elevated spermidine level and concomitant upregulation of genes involved in polyamine production were associated with a putatively anemia-derived increased spleen mass. Our data underline that the metal-chelating property of curcumin needs to be considered in feeding studies.

Heme Oxygenase-1 Is Involved in the Repair of Oxidative Damage Induced by Oxidized Fish Oil in Litopenaeus vannamei by Sulforaphane

Heme oxygenase-1 (HO-1), which could be highly induced under the stimulation of oxidative stress, functions in reducing the damage caused by oxidative stress, and sulforaphane (SFN) is an antioxidant. This study aims to investigate whether HO-1 is involved in the repair of oxidative damage induced by oxidized fish oil (OFO) in Litopenaeus vannamei by sulforaphane (SFN). The oxidative stress model of L. vannamei was established by feeding OFO feed (OFO accounts for 6%), and they were divided into the following four groups: control group (injected with dsRNA-EGFP and fed with common feed), dsRNA-HO-1 group (dsRNA-HO-1, common feed), dsRNA-HO-1 + SFN group (dsRNA-HO-1, supplement 50 mg kg-1 SFN feed), and SFN group (dsRNA-EGFP, supplement 50 mg kg-1 SFN feed). The results showed that the expression level of HO-1 in the dsRNA-HO-1 + SFN group was significantly increased compared with the dsRNA-HO-1 group (p < 0.05). The activities of SOD in muscle and GPX in hepatopancreas and serum of the dsRNA-HO-1 group were significantly lower than those of the control group, and MDA content in the dsRNA-HO-1 group was the highest among the four groups. However, SFN treatment increased the activities of GPX and SOD in hepatopancreas, muscle, and serum and significantly reduced the content of MDA (p < 0.05). SFN activated HO-1, upregulated the expression of antioxidant-related genes (CAT, SOD, GST, GPX, Trx, HIF-1α, Nrf2, prx 2, Hsp 70), and autophagy genes (ATG 3, ATG 5), and stabilized the expression of apoptosis genes (caspase 2, caspase 3) in the hepatopancreas (p < 0.05). In addition, knocking down HO-1 aggravated the vacuolation of hepatopancreas and increased the apoptosis of hepatopancreas, while the supplement of SFN could repair the vacuolation of hepatopancreas and reduce the apoptosis signal. In summary, HO-1 is involved in the repair of the oxidative damage induced by OFO in L. vannamei by SFN.

Changes in heme oxygenase level during development affect the adult life of Drosophila melanogaster

Heme oxygenase (HO) has been shown to control various cellular processes in both mammals and Drosophila melanogaster. Here, we investigated how changes in HO levels in neurons and glial cells during development affect adult flies, by using the TARGET Drosophila system to manipulate the expression of the ho gene. The obtained data showed differences in adult survival, maximum lifespan, climbing, locomotor activity, and sleep, which depended on the level of HO (after ho up-regulation or downregulation), the timing of expression (chronic or at specific developmental stages), cell types (neurons or glia), sex (males or females), and age of flies. In addition to ho, the effects of changing the mRNA level of the Drosophila CNC factor gene (NRF2 homolog in mammals and master regulator of HO), were also examined to compare with those observed after changing ho expression. We showed that HO levels in neurons and glia must be maintained at an appropriate physiological level during development to ensure the well-being of adults. We also found that the downregulation of ho in either neurons or glia in the brain is compensated by ho expressed in the retina.