254PActivation of complement cascade may trigger inflammation and fibrosis in Duchenne muscular dystrophy: a preclinical investigation on two murine models

In Duchenne muscular dystrophy (DMD), the absence of dystrophin causes repetitive cycles of degeneration/regeneration leading to inflammation, inefficient regeneration and recruitment of fibro-adipogenic progenitors (FAPs), creating an auto-reinforcing loop that exacerbates pathology. Recent data in dystrophic BL10- mdx mouse support an activation of complement system (CS) in reinforcing this loop: in particular, an overexpression of the complement component 1 (C1) in inflamed muscle has been linked to fibrosis via WNT- β-catenin-TGF-β2 axis (Florio et al.2023). In this context, the role of CS in DMD pathology deserves a deeper investigation, also considering the availability of CS inhibitors. We evaluated, via RT-PCR, the expression of C1q and C3, key CS components in gastrocnemius (GC) muscles of BL-10 mdx and of the more fibrotic D2-mdx model, at 4, 12 and 28 wks of age. Age- and strain-matched WT mice were used as controls. We found a strict correlation between C1q and C3 overexpression and the peak of unhealthy tissue in GC muscles of dystrophic mice in early stage of pathology. Conversely, our results were not in favour of a clear involvement of Tgfβ2 and β-catenin in fibrotic program. This process seems rather to be regulated via TGFβ1/MMP9/ADAMTS5, overexpressed in both models and matching the worsening of fibrosis signature. In addition, a marker of FAPs (PDGFrα) was upregulated at 28 wks in D2-mdx mice, in line with its more pro-fibrotic phenotype. Interestingly, in investigating the mechanism underlying the effects of JMV2894, a ghrelin mimetic chronically administered for 6 weeks to 4-5 week old D2-mdx mice (640 and 1280μg/kg/d, s.c.), we found a significant reduction of CS genes as C1q, C3, C3 receptor and FB/FD factors vs. untreated D2 mdx mice, paralleled by a downregulation of ADAMTS5/MMP9/TGFβ1 transcripts. Our results support an active role of CS in DMD, paving the way to preclinical studies to assess the therapeutic potential of CS inhibitors.