Beijing VDJBio (China)

Peptidic macrocycles have attracted increasing attention due to their well-defined structures and enhanced biological activities. However, efficient cyclization of residues lacking reactive side chains remains a significant challenge. Herein, we report a glycinamide-driven coumarin construction (GDCC) reaction that enables the in situ formation of coumarin scaffolds via condensation between C-terminal glycine residues and salicylaldehyde analogs under mild, metal- and catalyst-free conditions. While various salicylaldehyde derivatives afford efficient fluorescent labeling, symmetrical salicylaldehyde-based linkers uniquely promote intramolecular bis-glycine cyclization, generating intrinsically fluorescent peptide macrocycles with tunable topology and hydrophobicity. Notably, the optimal peptide 64 exhibits photophysical properties comparable or even superior to those of the coumarin gold standard, 7-(diethylamino)-4-methylcoumarin. The GDCC reaction displays broad substrate scope and excellent compatibility with both solid-phase and solution-phase peptide synthesis. Its potential in chemical biology is demonstrated by the streamlined construction of diverse fluorescent cyclic peptides, including RGD-based probes for live-cell imaging, peptide-drug conjugates for targeted doxorubicin delivery, and a panel of PD-1/PD-L1 interaction inhibitors with tunable activity.

Effective therapies for primary sclerosing cholangitis (PSC), a progressive cholestatic liver disease characterized by biliary inflammation and fibrotic damage, remain limited due to an incomplete elucidation of its underlying molecular mechanisms. Although N6-methyladenosine (m6A) RNA methylation has been implicated in hepatic pathophysiology, its role in PSC remains undefined. Here, we demonstrate that hepatocyte-specific deletion of Mettl3, a critical m6A methyltransferase, induces spontaneous PSC-like pathology characterized by ductular reaction and peribiliary fibrosis. Therapeutic restoration of Mettl3 through genetic knock-in or AAV8-mediated hepatocyte-specific overexpression significantly attenuated 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-induced PSC progression. Integrated single-cell and bulk transcriptomic profiles revealed an expansion of Trem2+ macrophages that interact with Spp1high cholangiocytes via the Cd44-Spp1 axis. Genetic ablation of Trem2 or cholangiocyte-specific deletion of Spp1 significantly suppressed DDC-induced biliary injury. Mechanistically, Mettl3-deficient hepatocytes secreted higher levels of macrophage-recruiting cytokines (such as Mif and Csf1), facilitating the recruitment of Trem2+ macrophage, which subsequently activated cholangiocytes through Cd44-Spp1 signaling, exacerbated biliary inflammation and fibrosis. Notably, pharmacological activation of Mettl3 in adult hepatocytes substantially mitigated PSC progression and liver fibrosis. Collectively, our findings establish hepatocyte Mettl3 deficiency as a pivotal driver of PSC pathogenesis and highlight the therapeutic potential of targeting the m6A epitranscriptome in cholestatic liver diseases.