Removing a specific part of the protein PTHrP in mice makes their growth‑plate cartilage smaller, speeds up the cells' maturation, and lowers the activity of the IGF‑1 system, which is important for bone growth.

Parathyroid hormone -related protein (PTHrP) regulates skeletal development by controlling epiphyseal growth cartilage. In mice, PTHrP contains three functional domains: the N-terminus, nuclear localization sequence (NLS), and C-terminus. The PTHrP (67 -139) region contains both the NLS and the C-terminus. Our research group previously generated C57BL/6 mice lacking this region (<i>Pthrp</i> &#x394;/&#x394;), resulting in reduced postnatal growth and shorter stature. This study aimed to define the functional role of PTHrP (67 -139) in chondrocytes in vitro and ex vivo. Epiphyseal growth cartilage from 1 -2-day-old Pthrp &#x394;/&#x394; mice was evaluated using histology, immunofluorescence, and qPCR. Primary chondrocytes from Pthrp &#x394;/&#x394; mice and PTHrP-transfected chondrocytes were cultured to assess proliferation and gene expression. <i>Pthrp</i> &#x394;/&#x394; mice showed significantly reduced epiphyseal cartilage height, including decreased resting, proliferative, and hypertrophic zone lengths. This was accompanied by increased mRNA expression of hypertrophic markers (<i>Ihh, Col10a1</i>). Epiphyseal cartilage from <i>Pthrp</i> &#x394;/&#x394; mice also exhibited elevated <i>Adamts5</i> and <i>Mmp13</i> expression, indicating enhanced extracellular matrix degradation. Primary chondrocytes from <i>Pthrp</i> &#x394;/&#x394; mice and chondrocytes transiently transfected with the PTHrP deletion construct (&#x394;NLS+CTERM) showed reduced proliferation and matrix production. Chondrocytes lacking PTHrP (67 -139) had decreased expression of <i>Col2a1</i> and <i>Acan</i>, along with reduced IGF-1/IGF-1R expression, suggesting impaired IGF-1 signaling. Loss of the PTHrP (67 -139) domain causes impaired proliferation, reduced matrix production, and increased extracellular matrix degradation in epiphyseal chondrocytes. These findings demonstrate that PTHrP (67 -139) is required to maintain chondrocytes in an immature state and that its absence leads to premature differentiation of epiphyseal growth plate chondrocytes.