Use of Second Harmonic Imaging and Fourier Transformation to Analyze Cartilage Repair in Mice Injected with a Novel Peptide CK2.1

Second harmonic generation (SHG) imaging is a powerful imaging tool that allows to study the distribution of the collagen network in cartilage. This imaging modality has been successfully utilized for visualizing physiologic and pathological changes in tissues and organs. However only recently the quantification of SHG images by Fourier Transform analysis allowed for successful quantification of the collagen network in cartilage. Here, we demonstrate that systemic injection of CK2.1, a novel mimetic peptide based on the Bone Morphogenetic Protein (BMP) receptor type I sequence, induced cartilage formation in mice and reassembly of collagen fibers. Intra-articular injections of slow release HGPCK2.1 demonstrated a robust regeneration of the damaged cartilage tissue and the collagen network. Collection of the forward (aligned) and backward (non-aligned) SHG allowed us to quantify the fibrillar distribution in peptide induced cartilage formation and repair. Our data show that the Forward SHG obtained by the collagen structures were greater compared to Backward SHG in CK2.1 in the cartilage of CK2.1 injected mice. These data suggest the cartilage elasticity to withstand stresses placed on the tissue is increased. Our data provide us insights into the peptides capabilities as a future therapeutic agent that can regenerate the lost cartilage to its native form.