Expression and distribution of surfactant proteins and lysozyme after prolonged hyperpnea

Abstract

We have induced prolonged hyperpnea in rats and examined the distribution of surfactant-associated proteins (SP-A and SP-B) and lysozyme in lamellar bodies (lb) and two alveolar fractions, one tubular myelin rich (alv-1) and the other tubular myelin poor (alv-2). We have also examined the expression of SP-A, SP-B, SP-C, and lysozyme mRNA in lung tissue and alveolar type II cells. Hyperpnea resulted in significant increases in lb SP-A, lysozyme, and phospholipid (PL) but no change in the protein-to-PH ratios, suggesting that lb stoichiometry is constant. The SP-A and SP-B-to-PL ratios were 33 and 18 times greater, respectively, in control alv-1 than in lb, suggesting that alv-1 is enriched with these proteins. In contrast, the lysozyme-to-PL ratio was similar in control alv-1 and lb. Hyperpnea did not alter the alv-1 SP-A or SP-B-to-PL ratios, suggesting some constant stoichiometry to their lipid association; however, the lysozyme-to-PL ratio was reduced. Whereas hyperpnea significantly elevated the PL, SP-A, and lysozyme levels in alv-2, the SP-B level was unchanged. We suggest that surfactant-associated lysozyme is secreted with lb, the majority of SP-A is linked to lipid secretion but not necessarily with lb, and the majority of SP-B secretion is independent of PL secretion. Hyperpnea did not alter the mRNA expression of SP-A, SP-B, SP-C, or lysozyme in alveolar type II cells, but expression of SP-A and SP-B mRNA was significantly increased in lung tissue.