Ontogeny of proteolytic signaling and antioxidant capacity in fetal and neonatal diaphragm

Whereas upregulation of protein degradation pathways contributes to the development of muscle weakness in response to muscle injury and inflammation in the adult diaphragm, less is known about the preterm diaphragm. Muscle development during the antenatal and early postnatal periods normally results in net growth. However, the structural and functional immaturity of the preterm diaphragm may predispose it to injury and inflammation induced by adverse antenatal and postnatal exposures. Characterization of the ontogeny of diaphragm protein degradation pathways in early life is essential to recognise altered signaling pathways under pathologic conditions in preterm babies.

We assessed the relative role of the major proteolytic pathways and antioxidant capacity during muscle maturation in ovine fetuses and lambs from 75 d to 200 d post-conceptual age. Gene expression and protein content of calpain and caspase 3 exhibited a similar profile with advancing gestation, increasing from 75 d to 100 d/128 d and subsequently decreasing gradually toward the end of gestation. In contrast, ubiquitin conjugating and ligase genes do not change during gestation. All proteolytic genes examined (except Ubiquitin) are up-regulated rapidly after delivery, with a similar developmental trend observed in calpain II protein content as well as calpain protease activity. In contrast, antioxidant gene expression demonstrated a steady increase from 75 d gestation until 24 h after birth, followed by a significant reduction at 7 w of postnatal age (p ≤ 0.002). The proteolytic signaling and antioxidant capacity patterns reflect the adaptive process to metabolic change and muscle maturity with development.