Collagen hybridizing peptide to target in vivo misfolded collagen in OI zebrafish

: Osteogenesis imperfecta (OI) is a heritable connective tissue disorder characterized by defects in collagen I, leading to increased bone fragility and turnover. The zebrafish Chihuahua (Chi/+), carrying a p.(Gly736Asp) substitution in the α1(I) chain, recapitulates key features of human OI, including the presence of misfolded collagen I in extracellular matrix. In this study, we evaluated the specificity of a fluorescently labeled collagen hybridizing peptide (Cy5-CHP) for detecting in vivo misfolded collagen I in adult zebrafish. The CHP or the scrambled control peptides were injected intraperitoneally into WT and Chi/+ zebrafish, and average radiant efficiency was quantified at 24 and 72 h post-injection (hpi) in the vertebral column, cranium and heart, representing collagen I-rich organs, as well as the brain, a collagen I-poor tissue. Our results revealed Cy5-CHP specific binding to collagen I-rich tissues in Chi/+ zebrafish at 24 hpi, with minimal signal in the brain, whereas low signal was detectable across all tissues in WT. Cy5-CHP fluorescence was reduced by 72 hpi in all samples, consistent with the low binding affinity of the peptide. Histological analyses confirmed the co-localization of Cy5-CHP with collagen fibers in the endplates of Chi/+ vertebrae at 24 hpi. These findings provide the first in vivo evidence in zebrafish that Cy5-CHP selectively binds misfolded collagen, showing preferential accumulation in collagen I-rich tissues in OI. Overall, the results support the use of Cy5-CHP as a sensitive tool for detecting pathologic collagen and as a potential platform for tissue-targeted drug delivery in OI and other collagen-related disorders.