mNLS-CPP-WSTF is a nuclear localization signal (NLS)-cell penetrating peptide derived from the mouse WSTF sequence. This compound significantly inhibits the interaction between GABARAP and WSTF, WSTF degradation, and the expression of inflammatory genes. It effectively alleviates chronic inflammation, liver fibrosis, and cartilage damage in mouse models of metabolism-associated steatohepatitis (MASH) and osteoarthritis (OA). mNLS-CPP-WSTF shows research potential for chronic inflammatory diseases such as MASH and OA.