The Blue Light-Dependent Phosphorylation of the CCE Domain Determines the Photosensitivity of Arabidopsis CRY2

Artesunate Induces Ferroptosis in Hepatic Stellate Cells and Alleviates Liver Fibrosis via the ROCK1/ATF3 Axis

Background and Aims

Development of fibrosis in chronic liver disease requires activation of hepatic stellate cells (HSCs) and leads to a poor outcome. Artesunate (Art) is an ester derivative of artemisinin that can induce ferroptosis in HSCs, and activated transcriptional factor 3 (ATF3) is an ATF/CREB transcription factor that is induced in response to stress. In this study, we examined the role of the Rho-associated protein kinase 1 (ROCK1)/ATF3 axis in Art-induced ferroptosis in HSCs.

Methods

HSC activation and ferroptosis were studied in vitro by western blotting, polymerase chain reaction, immunofluorescence, and other assays. ATF3 electrophoretic mobility and ROCK1 protein stability were assayed by western blotting. Immunoprecipitation was used to detect the interaction of ROCK1 and ATF3, as well as ATF3 phosphorylation. A ubiquitination assay was used to verify ROCK1 degradation. Atf3-interfering and Rock1-overexpressing mice were constructed to validate the anti-hepatic fibrosis activity of Art in vivo.

Results

Art induced ferroptosis in HSCs following glutathione-dependent antioxidant system inactivation resulting from nuclear accumulation of unphosphorylated ATF3 mediated by ROCK1-ubiquitination in vitro. Art also decreased carbon tetrachloride-induced liver fibrosis in mice, which was reversed by interfering with Atf3 or overexpressing Rock1.

Conclusions

The ROCK1/ATF3 axis was involved in liver fibrosis and regulation of ferroptosis, which provides an experimental basis for further study of Art for the treatment of liver fibrosis.

Structural insights into photoactivation of plant Cryptochrome-2

Cryptochromes (CRYs) are evolutionarily conserved photoreceptors that mediate various light-induced responses in bacteria, plants, and animals. Plant cryptochromes govern a variety of critical growth and developmental processes including seed germination, flowering time and entrainment of the circadian clock. CRY's photocycle involves reduction of their flavin adenine dinucleotide (FAD)-bound chromophore, which is completely oxidized in the dark and semi to fully reduced in the light signaling-active state. Despite the progress in characterizing cryptochromes, important aspects of their photochemistry, regulation, and light-induced structural changes remain to be addressed. In this study, we determine the crystal structure of the photosensory domain of Arabidopsis CRY2 in a tetrameric active state. Systematic structure-based analyses of photo-activated and inactive plant CRYs elucidate distinct structural elements and critical residues that dynamically partake in photo-induced oligomerization. Our study offers an updated model of CRYs photoactivation mechanism as well as the mode of its regulation by interacting proteins.

The oligomeric structures of plant cryptochromes

Cryptochromes (CRYs) are a group of evolutionarily conserved flavoproteins found in many organisms. In plants, the well-studied CRY photoreceptor, activated by blue light, plays essential roles in plant growth and development. However, the mechanism of activation remains largely unknown. Here, we determined the oligomeric structures of the blue-light-perceiving PHR domain of Zea mays CRY1 and an Arabidopsis CRY2 constitutively active mutant. The structures form dimers and tetramers whose functional importance is examined in vitro and in vivo with Arabidopsis CRY2. Structure-based analysis suggests that blue light may be perceived by CRY to cause conformational changes, whose precise nature remains to be determined, leading to oligomerization that is essential for downstream signaling. This photoactivation mechanism may be widely used by plant CRYs. Our study reveals a molecular mechanism of plant CRY activation and also paves the way for design of CRY as a more efficient optical switch.

Exploration of the Effect of Blue Light on Functional Metabolite Accumulation in Longan Embryonic Calli via RNA Sequencing

Light is an important factor that affects the synthesis of functional metabolites in longan embryogenic calli (ECs). However, analysis of the effect of light on functional metabolites in longan ECs via RNA sequencing has rarely been reported and their light regulation network is unclear. The contents of various functional metabolites as well as the enzymatic activities of superoxide dismutase and peroxidase and the level of H₂O₂ in longan ECs were significantly higher under blue light treatment than under the other treatments (dark, white). In this study, we sequenced three mRNA libraries constructed from longan ECs subjected to different treatments. A total of 4463, 1639 and 1806 genes were differentially expressed in the dark versus blue (DB), dark versus white (DW) and white versus blue (WB) combinations, respectively. According to GO and KEGG analyses, most of the differentially expressed genes (DEGs) identified were involved in transmembrane transport, taurine and hypotaurine metabolism, calcium transport and so forth. Mapman analysis revealed that more DEGs were identified in each DB combination pathway than in DW combination pathways, indicating that blue light exerts a significantly stronger regulatory effect on longan EC metabolism than the other treatments. Based on previous research and transcriptome data mining, a blue light signaling network of genes that affect longan functional metabolites was constructed and HY5, PIF4 and MYC2 were shown to be the key regulatory genes in the network. The results of this study demonstrate that the expression levels of phase-specific genes vary with changes in longan EC functional metabolites.