Respiratory Distress and Early Neonatal Lethality in Hspa4l/Hspa4 Double-Mutant Mice

Heat shock proteins HSPA4L and HSPA4 are closely related members of the HSP110 family and act as cochaperones. We generated Hspa4l(-1-) Hspa4(-1-) mice to investigate a functional complementarity between HSPA4L and HSPA4 during embryonic development. Hspa4l(-1-) Hspa4(-1-) 2 embryos exhibited marked pulmonary hypoplasia and neonatal death. Compared with lungs of wild- type, Hspa4l(-1-) , and Hspa4(-1-) embryos, Hspa4l(-1-) Hspa4(-1-) lungs were characterized by diminished saccular spaces and increased mesenchymal septa. Mesenchymal hypercellularity was determined to be due to an increased cell proliferation index and decreased cell death. A significant increase in expression levels of prosurvival protein B cell leukemia/ lymphoma 2 may be the cause for inhibition of apoptotic process in lungs of Hspa4(-1-) Hspa4l(-1-) embryos. Accumulation of glycogen and diminished expression of surfactant protein B, prosurfactant protein C, and aquaporin 5 in saccular epithelium suggested impaired maturation of type II and type I pneumocytes in the Hspa4l(-1-) Hspa4(-1-) lungs. Further experiments showed a significant accumulation of ubiquitinated proteins in the lungs of Hspa4l(-1-) Hspa4(-1-) embryos, indicating an impaired chaperone activity. Our study demonstrates that HSPA4L and HSPA4 collaborate in embryonic lung maturation, which is necessary for adaptation to air breathing at birth.