Effect of maternal steroid on developing diaphragm integrity.

Area of Science:

• Neonatal physiology
• Developmental biology
• Pharmacology

Background:

• Antenatal steroids are crucial for premature infant respiratory distress but may affect other organs.
• Potential adverse effects of antenatal steroids on developing respiratory muscles require investigation.

Purpose of the Study:

• To investigate the impact of maternal steroid administration on postnatal respiratory muscle function in developing rats.
• To elucidate the underlying mechanisms of steroid-induced myopathy in newborn rat diaphragms.

Main Methods:

• Pregnant rats received betamethasone injections before birth.
• Diaphragm contractile function was assessed at 2, 7, and 21 days postnatal age (PNA).
• Myosin heavy chain (MHC) isoform expression, atrophy-related genes, and intracellular signaling pathways were analyzed.

Main Results:

• Betamethasone treatment led to decreased diaphragm force production, reduced fatigue resistance, and lower fast-fiber content at 21 days PNA.
• Maternal steroid exposure impaired anabolic signaling (Akt, 4E-BP1) and altered MHC isoform composition in 21-day-old diaphragms.
• These detrimental effects were specific to 21 days PNA, with no significant impact observed at 2 or 7 days PNA.

Conclusions:

• Maternal betamethasone administration causes significant postnatal diaphragmatic dysfunction by 21 days PNA.
• The observed dysfunction is associated with reduced MHC II protein expression and impaired anabolic signaling.
• Developmental changes in MHC fiber composition and protein signaling mediate the age-specific diaphragm dysfunction.