Lack of bombesin receptor–activated protein attenuates bleomycin-induced pulmonary fibrosis in mice

Bombesin receptor–activated protein (BRAP) was found to express in the interstitial cells of human fibrotic lungs with unknown function. Its homologous protein, encoded by BC004004 gene, was also present in mouse lung tissues. We used BC004004(−/−) mice which lack BRAP homologous protein expression to establish a bleomycin-induced lung fibrotic model. After bleomycin treatment, BC004004(−/−) mice exhibited attenuation of pulmonary injury and less pulmonary fibrosis. Fibroblasts from BC004004(−/−) mice proliferated at a lower rate and produced less collagen. Autophagy-related gene 5 (ATG5) was identified as a partner interacting with human BRAP. Lacking BRAP homologous protein led to enhanced autophagy activity in mouse lung tissues as well as in isolated lung fibroblasts, indicating a negative regulatory role of this protein in autophagy via interaction with ATG5. Enhanced autophagy process in fibroblasts due to lack of BRAP homologous protein might contribute to the resistance of BC004004(−/−) mice to pulmonary fibrosis.