Relationship between Notch receptors and hyperoxia-induced lung injury in newborn rats

Abstract

To investigate role of Notch1–3 in hyperoxia-induced lung injury in newborn rat exposed to 85% O₂, SD rat litters born on the 22th day were randomly divided into two groups: room air group and hyperoxia group. The animals were sacrificed 1, 4, 7, 10, 14 and 21 days after continued exposure to oxygen (n=40, oxygen>0.85) or room air (n=40). 6 rats each group were used to assess lung histological changes by HE staining and expression of Notch in lungs by immunohistochemistry. Total RNA was extracted by Trizol reagent from frozen lung tissues. Notch mRNA were measured by reverse transcription polymerase chain reaction (RT-PCR). Our results showed that 7, 14 and 21 days after O₂ exposure, hyperoxia group showed lung injury characterized by pulmonary edema, hemorrhage and lung development arrest. Positive staining for Notch1, Notch 2 in hyperoxia group was much lower than those in room air group at all time points (P<0. 01,P<0.05), but compared with the controls, the hyperoxia group showed higher expression of Notch3 (P>0.05). Immunostained cells were typically airways epithelia, alveolar epithelial and inflammatory cells, and fibroblasts in hyperoxia group (P<0.01). Notch mRNA levels showed similar change as protein level (P<0.01). It is concluded that the prolonged exposure to 85% O₂ resulted in abnormal expression of Notch receptors, which might contribute to the pathogenesis of hyperoxia-induced lung injury in newborn rats. The decreased inhibition of Notch1 might be one of the protective reaction and major mechanisms for proliferation/differentiation of type II alveolar epithelial cells. The up-regulation of Notch3 activity might result in the lung development arrest of the newborn rats.

Keywords

Notch receptor / hyperoxia / lung injury / newborn

References

[1] AveryG B, FletcherM A, MacDonaldM G. Neonatology Pathophysiology & Management of the Newborn, 19995th ed.Philadelphia, Lippincott Williams & Wilkins: 541-541

[2] Artavanis-TsakonasS, RandM D, LakeR J. Notch signaling: cell fate control and signal interaction in development. Science, 1999, 284(5814): 770-770

[3] BlaumuellerC M, QiH, ZagourasP, et al. . Intracellular cleavage of Notch lead to a hetrodimeric receptor on the plasma membrane. Cell, 1997, 90(2): 281-281

[4] TakaakiI, UdakaN, YazawaT, et al. . Basic helix-loophelix transcription factors regulate the neuroendocrine differentiation of fetal mouse pulmonary epithelium. Development, 2000, 1273913-3913

[5] PostM C, TernetM, HoganB L. Notch/Delta expression in the developing mouse lung. Mech Dev, 2000, 98(1–2): 95-95

[6] TaichmanD B, LoomesK M, SchachtnerS K, et al. . Notch1 and Jagged1 expression by the developing pulmonary vasculature. Dev Dyn, 2002, 225(2): 166-166

[7] CamposA H, WangW, PollmanM J, et al. . Determinants of Notch-3 receptor expression and signaling in vascular smooth muscle cells: implications in cell-cycle regulation. Circ Res, 2002, 91(11): 999-999

[8] MitsiadisT A, FriedK, GoridisC. Reactivation of Delta-Notch signaling after injury: complementary expression pattern of ligand and receptor in dental pulp. Exp Cell Res, 1999, 246(2): 313-313

[9] DangT P, EichenbergerS, GonzalezA, et al. . Constitutive activation of Notch3 inhibits terminal epithelial differentiation in lungs of transgenic mice. Oncogene, 2003, 22(13): 1988-1988