Circadian rhythm of surfactant protein A, B and C mRNA in rats

Kim, Chung Mi; Sohn, Jang Won; Yang, Seok Chul; Yoon, Ho Joo; Shin, Dong Ho; Park, Sung Soo

Abstract

BACKGROUND: All organisms have developed an internal timing system capable of reacting to and anticipating environmental stimuli with a program of appropriately timed metabolic, physiologic, and behavioral events. The alveolar epithelial type II cell of mammalian lung synthesizes, stores, and secretes a lipoprotein pulmonary surfactant, which functions to stabilize alveoli at low lung volumes.
METHODS
The authors investigated the diurnal variation of surfactant protein A, B and C mRNA accumulation. The diurnal variation on gene expression of surfactant protein A, B and C were analysed using filter hybridization at 9 AM, 4 PM and 11 PM. Lung SP-A protein content was determined by double sandwich ELISA assay using a polyclonal antiserum raised in rabbits against purified rat SP-A.
RESULTS
1. The accumulation of SP-A mRNA at 4 PM was significantly decreased 23.5% compared to the value at 9 AM (p<0.05). 2. The accumulation of SP-B mRNA at 4 PM and 11 PM was decreased by 15.1% and 5.7%, respectively, compared to the value at 9 AM (p=0.07, p=0.69). 3. The accumulation of SP-C mRNA at 4 PM and 11 PM was decreased by 6.8% and 7.7%, respectively, compared to the value at 9 AM (p=0.38, p=0.57). 4. Total lung SP-A content at 4 PM and 11 PM was increased by 5.3% and 15.9%, respectively, compared to the value at 9 AM (p=0.64, p=0.47).
CONCLUSION
These findings represent diurnal variation of surfactant proteins mRNA expression in vivo. This results suggested the diurnal variation of hydrophilic surfactant protein rather than hydrophobic surfactant proteins.