Adult zebrafish and neonatal mice can fully regenerate their hearts after partial amputation through the proliferation of preexisting cardiomyocytes (CMs). However, the adult mammalian heart has limited regenerative capability following cardiac damage. The reason for this phenomenon remains elusive. Here, we find that docosahexaenoic acid (DHA) is accumulated only in the injured hearts of zebrafish and neonatal mice, but not of adult mice, which coincides with the upregulation of DHA synthesis genes in CMs, fibroblasts, and macrophages near the injury areas. Inhibition of Fads2, a DHA synthesis enzyme, impairs heart regeneration in both zebrafish and neonatal mice. Injection of DHA remodels the transcriptome from injury response to regeneration response and improves cardiac function in adult mice after myocardial infarction. Interestingly, DHA facilitates CM proliferation but inhibits fibrosis and inflammation. Mechanistically, only DHA, but not oleic acid (OA), can trigger the peroxisome proliferator-activated receptor d (PPARD) to bind to the promoter regions of heart regeneration-related genes, such as Mef2d, Phlda3, and Txndc5, to regulate their expression. Molecular docking, molecular dynamics simulations, and mutagenesis experiments suggest that DHA binds to PPARD in a distinct manner compared to OA, which may help explain their differing abilities to influence the expression of heart regeneration genes. Our findings demonstrate that the DHA signal plays an essential and evolutionarily conserved role in heart regeneration and provide a therapeutic potential for myocardial infarction.

The endocrine system is crucial for maintaining overall homeostasis. However, its cellular signatures have not been elucidated during aging. Here, we conducted the first-ever single-cell transcriptomic profiles from eight endocrine organs in young and aged mice, revealing the activation of cell-type-specific aging pathways, such as loss of proteostasis, genomic instability and reactive oxygen species (ROS). Among six sex-shared endocrine organs, aging severely impaired gene expression networks in functional endocrine cells, accompanied by enhanced immune infiltration and unfolded protein response (UPR). Mechanism investigations showed that expanded aging-associated exhausted T cells activated MHC-Ⅰ–UPR axis across functional endocrine cells by releasing GZMK. The inhibition of GZMK receptors by small chemical molecules counteracted the UPR and senescence, suggesting the immune infiltration is a possible driver of endocrine aging. Machine learning identified CD59 as a novel aging feature in sex-shared functional endocrine cells. For two sex-specific endocrine organs, both aged ovaries and testes showed enhanced immune responses. Meanwhile, cell-type-specific aging-associated transcriptional changes revealed an enhanced ROS mainly in aged theca cells of ovaries, while aged spermatogonia in testes showed impaired DNA repair. This study provides a comprehensive analysis of endocrine system aging at single-cell resolution, offering profound insights into mechanisms of endocrine aging.

Diffuse alveolar damage (DAD) is recognized as a deadly type of acute inflammatory lung injury caused by toxic inhalants, but its cellular and molecular pathogenesis remains largely unclear. In this study, by using a mouse model of ricin-induced DAD, we explored the heterogeneity of recruited monocyte (Mono) and Mono-derived interstitial macrophage (IM) in the DAD lung. There was the development of 2 distinct IM subsets, namely IM^pi (pro-inflammatory) and IM^ai (anti-inflammatory), from recruited Mono^pi. A subset of recruited Mono^pi could get the proliferating phenotype (namely pMono^pi), and meanwhile pMono^pi served as the intermediate of Mono^pi-to-IM^ai transition. The presence of growth differentiation factor 15 (GDF15) facilitated Mono^pi-to-pMono^pi-to-IM^ai transition, whereas GDF15 deficiency exerted the negative feedback effect of enhancing Mono^pi-to-IM^pi shift. These findings provided a cell differentiation landscape for Mono and IM in the DAD lung, which would promote a deeper understanding of cellular immunology of DAD and offer a theoretical basis for developing novel therapeutic strategies against acute lung injury.

Respiratory syncytial virus (RSV) exploits host proteases to enhance its replication efficiency; however, the precise mechanisms remain unclear. Through high-throughput screening, we identified four matrix metalloproteinase 9 (MMP-9) inhibitors (including JNJ0966 and doxycycline hyclate) that suppress RSV infection in vitro and in vivo. Mechanistic studies revealed a proteolytic cascade wherein MMP-9 cleaves transglutaminase 2 (TGM2) at the PVP³⁷⁵↓VR site, generating an N-terminal fragment (1–375) that activates its protein disulfide isomerase (PDI) activity. This TGM2-dependent PDI activity catalyzes disulfide bond rearrangement in the RSV fusion glycoprotein (F), enabling F protein maturation, a prerequisite for membrane fusion and syncytium formation—key processes driving late-stage viral propagation. Genetic ablation of MMP-9 significantly attenuated RSV infectivity, while pharmacological inhibition reduced pulmonary viral loads and mitigated lung pathology in infected mice. Our study defines a unified MMP-9→TGM2→F axis as the core mechanism driving RSV replication and validates MMP-9 as a therapeutic target.