Thermophilic Fungus Uses Anthraquinones to Modulate Ferrous Excretion, Sterol-Mediated Endocytosis and Iron Storage in Response to Cold Stress

To date, there is no real physiological mechanisms for iron excretion in eukaryote, and no physiological "actuator" that can control all the three fundamental biologic processes of absorption, storage and excretion. Here we observed that the accumulation of anthraquinones by Thermomyces dupontii under cold stress can achieve this process. Through mutation analysis, we found that mutant {Delta}An deficiency in anthraquinones accumulated ferrous and total free iron due to adopting a rare lifestyle with no endocytosis but accumulation of membrane-derived vesicles. Anthraquinone complement indicated that the vesicles in {Delta}An could coat the extrinsic anthraquinone-induced granules to prevent contact with the fungal interiors. Detailed chemical investigation on {Delta}An led to characterization of a rare oxygen-free ergosterene with unstable nature in air as the major membrane steroid in {Delta}An, suggesting hypoxia inner in {Delta}An cells, consistent with dramatically low oxygen-consuming rates in {Delta}An. A series of physiological and metabolic analysis indicated anthraquinones were involved in exporting ferrous and promoting formation of oxygen-containing metabolites, including ergosterols for endocytosis and iron chelators for iron storage. Moreover, we found that both the anticancer agent mitoxantrone with well know-cardiotoxicity side effect and the major terpenoid-derived polycyclic aromatics from Danshen for treating cardiovascular disease showed potent ferrous transporting capabilities in human cancer cells. Our findings provide a novel insight into the underlying mechanisms of polycyclic aromatics in nature and pharmacology, and offer new strategy for developing potential therapeutics and agents for membrane transport, iron homestasis and anticold. Graphical AbstractUp to now, regulation of iron homeostasis by metabolites have rarely been characterized. Moreover, no excretory mechanisms for iron in fungi have been reported. In this study, we found that Thermomyces dupontii can accumulate a large amount of anthraquinones under cold stress. The anthraquinones can release free ferric ion, reduce ferric to ferrous ions, and export ferrous ions, greatly enhancing thermophilic fungus to survive in the bio-system environment. Furthermore, lack of the anthraquinones can inhibit oxygen-dependent ergosterol mediated endocytosis, leading to an self-imposed isolation via oxygen-free ergosterene-mediated cell membranes. Importantly, the well known anthraquinone compound Mitoxantraquinone for anticancer and the main terpenoid polycyclic aromatic metabolites in traditional Chinese medicine Danshen for the treatment of cardiovascular diseases both exhibit strong ferrous ions transport capabilities. Our findings provided new insights for developing potential therapies and drugs for iron homeostasis and drug delivery. O_FIG O_LINKSMALLFIG WIDTH=196 HEIGHT=200 SRC="FIGDIR/small/605589v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@114551eorg.highwire.dtl.DTLVardef@1e03589org.highwire.dtl.DTLVardef@dad51borg.highwire.dtl.DTLVardef@dd0601_HPS_FORMAT_FIGEXP M_FIG C_FIG