Evaluation of IHH, PTCH1, and SMO protein immunohistochemistry in the human mandibular condyle at fetal stages from 30 to 80 mm greatest length

Abstract

This study evaluated the morphogenesis of the temporomandibular joint (TMJ) in human fetuses during the third month of gestation through the analysis of immunohistochemistry for the proteins Indian Hedgehog (IHH), Patched-1 (PTCH1), and Smoothened (SMO). These proteins are critical components of the Hedgehog signaling pathway in the embryonic development. Together, they transduce essential intracellular signals for cartilage and bone development and regulate chondrocyte differentiation and growth as part of the synergistic molecular mechanisms that converge to form synovial joints, including the TMJ. A prospective observational study was conducted on six human fetuses at fetal stages ranging from 30 to 80 mm greatest length (estimated to range between 9 and 12 weeks gestational age). Hematoxylin-eosin staining was used for morphological analysis, and protein immunostaining was assessed through immunohistochemistry. The percentage of immunostaining was quantified using digital image analysis with ImageJ software. IHH immunostaining peaked at the 30 mm stage (4.63%), decreased at 60 mm (2.16%), increased at 70 mm (3.70%), and declined again at 80 mm (2.75%). PTCH1 showed the highest immunostaining at 30 mm (5.35%), with a progressive decrease to its lowest level at 80 mm (1.18%). SMO immunostaining was highest at 30 mm (4.07%), decreased at 60 mm (1.80%), and increased at 70 mm (2.63%) and 80 mm (3.52%). Strong correlations were found between IHH and PTCH1 (rho = 0.70) and between IHH and SMO (rho = 0.70), while PTCH1 and SMO showed a moderate correlation (rho = -0.30). These findings highlight the dynamic protein activity and their critical roles in TMJ morphogenesis.