When the skin suffers from burns or frostbite, its normal structure and function are severely damaged, leading to problems such as inflammation, oxidative stress and difficulties in vascularization, which result in difficult wound healing. Currently, the existing treatment options have limitations in efficacy. The pH value of the burns and frostbite (B/F) wound microenvironment shows a dynamic change: it is acidic in the initial stage, gradually alkalizes as the repair process progresses, and then returns to a slightly acidic state in the later stage. Based on this, we designed a pH-responsive bilayer hydrogel with sequential release of morin-based nanoparticles and basic fibroblast growth factor (bFGF) for the treatment of B/F wounds. 4-hydroxyphenylboronic acid pinacol ester (PAPE) modified fucoidan (Fu), chitosan (Cs) and morin self-assembled to form nanoparticles (CFMNPs), which exhibited excellent pH sensitivity. Then, using methacrylated hyaluronic acid (MeHA) as the main component, taking advantage of the concentration difference and the property that MeHA is easily degraded in an acidic environment, a 0.8 % MeHA lower layer hydrogel loaded with CFMNPs and a 2 % MeHA upper layer hydrogel loaded with bFGF were prepared. In vitro experiments confirmed the pH responsiveness and cytocompatibility of the bilayer hydrogel. In vivo experiments on mouse B/F wounds verified that the bilayer hydrogel can achieve sequential release of active ingredients according to the pH changes of the B/F wound, effectively inhibit inflammation, resist oxidative stress, promote new blood vessel formation, and ultimately accelerate wound healing. This provides a highly potential and efficient new strategy for the treatment of B/F wounds.

Atherosclerosis is a common vascular disease that poses a serious threat to global health. However, the mechanism underlying the pathogenesis and progression of atherosclerosis remains elusive. We analysed the expression of deubiquitinating enzymes in human atherosclerotic lesions and found that USP25 was significantly downregulated. The role of USP25 in atherosclerosis was validated in mouse models with an ApoE^-/- background. The protein substrates of USP25 were identified by mass spectrometry. Various biochemical methods were adopted to study the role of USP25 in signal transduction. USP25 was predominantly expressed in macrophages in atherosclerotic lesions, and ablation of macrophagic USP25 significantly exacerbated atherosclerosis in ApoE^-/- mice accompanied by increased lipid deposition, macrophage infiltration, and vascular inflammation. Upon stimulation with ox-LDL or TNF-α, USP25 inhibited inflammatory responses in macrophages by restricting the NF-κB pathway. Mass spectrometry analysis identified RIPK1 as a USP25 substrate. Mechanistically, USP25 physically interacted with RIPK1 and removed K63 ubiquitin chains from RIPK1 via the C178 active site, thereby attenuating RIPK1-mediated signal transduction. This study elucidated the function and molecular mechanism of USP25 in atherosclerosis, identifying USP25 as a beneficial regulator for this disease. This work was supported by the Natural Science Foundation of Zhejiang Province (LZ24H090003 to X.W. and LTGY23H090001 to W.W.), the National Natural Science Foundation of China (82150710557 and 82293642 to W.S.; 81971143 to X.W., and 82271347 to G.W.), and Wenzhou Municipal Science and Technology Bureau (Y2021094 to J.H.).