# Lactucopicrin promotes the autophagic degradation of MAP2K4/MKK4 by mediating CCDC50 palmitoylation to alleviate osteoarthritis progression

## TL;DR

Lactucopicrin helps reduce osteoarthritis by boosting autophagy through a new pathway involving protein palmitoylation and degradation.

## Contribution

The study identifies a novel regulatory axis involving ZDHHC4, CCDC50, and MAP2K4/MKK4 in autophagy and OA.

## Key findings

- Lactucopicrin reduces cartilage degeneration and preserves matrix integrity in an OA mouse model.
- Lactucopicrin enhances ZDHHC4 activity, promoting CCDC50 palmitoylation and MAP2K4/MKK4 degradation.
- The study reveals a new link between palmitoylation, autophagy, and chondrocyte senescence in OA.

## Abstract

Macroautophagy/autophagy plays a crucial role in maintaining cellular homeostasis and protecting against osteoarthritis (OA). Its dysregulation contributes to OA progression by promoting chondrocyte senescence, inflammation, and cartilage degradation. Enhancing autophagic activity thus represents a promising therapeutic strategy for OA. In this study, we identified lactucopicrin (LCP) as an effective autophagy activator that alleviates OA progression in a mouse model induced by the destabilization of the medial meniscus, by reducing cartilage degeneration and preserving matrix integrity. Mechanistically, LCP enhances ZDHHC4-catalyzed palmitoylation of the cargo receptor CCDC50, facilitating the selective autophagic degradation of MAP2K4/MKK4, leading to the suppression of MAPK/JNK signaling and the attenuation of chondrocyte senescence. Structural analysis reveals that LCP directly binds to His72 of ZDHHC4 via its p-hydroxybenzoic acid moiety, boosting enzymatic activity and promoting selective autophagy. These findings establish a novel ZDHHC4-CCDC50-MAP2K4/MKK4-MAPK/JNK regulatory axis linking palmitoylation, autophagy, and senescence, and identify LCP as a promising agent for targeting this pathway to inhibit OA progression. Furthermore, this study provides mechanistic insights into the crosstalk between autophagy, protein palmitoylation, and cellular senescence in degenerative joint disease.

Abbreviation: ABE: acyl-biotin exchange; ADAMTS5: ADAM metallopeptidase with thrombospondin type 1 motif 5; CCDC50: coiled-coil domain containing 50; COL2A1: collagen, type II, alpha 1; COL10A1: collagen, type X, alpha 1; DARTS: drug affinity responsive target stability; DHHC: Asp-His-His-Cys catalytic motif; GOT1/AST: glutamic-oxaloacetic transaminase 1, soluble; GPT/ALT: glutamic pyruvic transaminase, soluble; H2O2: hydrogen peroxide; LCP: lactucopicrin; IL6: interleukin 6; MAPK/JNK: mitogen-activated protein kinase; MAP2K4/MKK4: mitogen-activated protein kinase kinase 4; MMP13: matrix metallopeptidase 13; OA: osteoarthritis; p-MAPK/JNK: phosphorylated mitogen-activated protein kinase; SASP: senescence-associated secretory phenotype; SA-GLB1/β-gal: senescence-associated galactosidase, beta 1; ZDHHC: zinc finger, DHHC domain containing.