Chronic intermittent hypoxia exacerbates the progression of NAFLD via SPP1-mediated inflammatory polarization in macrophages

Abstract

Background: Obstructive sleep apnea (OSA), characterized by chronic intermittent hypoxia (CIH), has been implicated in the development and progression of non-alcoholic fatty liver disease (NAFLD). The importance of macrophages in NAFLD pathogenesis has been well-documented, yet the impact of CIH on liver macrophages and the underlying mechanisms during NAFLD progression remain largely unclear.

Methods: In this study, we established two types of NAFLD murine models and simultaneously exposed the mice to CIH or room air condition to evaluate the impact of CIH on hepatic pathophysiology and liver macrophage status. In vitro experiments utilizing bone marrow-derived macrophages (BMDMs) were conducted to validate the CIH-induced macrophage polarization and its contribution to hepatocyte injury. Furthermore, the role of secreted phosphoprotein 1 (SPP1) in CIH-mediated macrophage polarization was investigated.

Results: CIH exposure significantly exacerbated liver injury in both high-fat diet and methionine-choline-deficient diet induced NAFLD models, as indicated by increased hepatic inflammation and fibrosis. Further liver macrophage analysis revealed a marked increase in macrophage accumulation and a significant shift toward M1 polarization under CIH conditions during NAFLD progression. Similarly, CIH-exposed BMDMs demonstrated pronounced M1 polarization and pro-inflammatory activation, which aggravated lipid-induced hepatocyte injury. Transcriptomic analysis identified consistent upregulation of Spp1 in both CIH-exposed BMDMs and liver macrophages from NAFLD murine models. Elevated SPP1 expression was also confirmed in CIH-exposed macrophages and NAFLD liver tissues. Functional validation studies revealed that SPP1 knockdown in macrophages effectively attenuated CIH-induced M1 polarization and reduced associated inflammatory and fibrotic injury in hepatocytes.

Conclusion: CIH promotes inflammatory polarization of liver macrophages through the upregulation of SPP1, thereby exacerbating hepatocyte injury and accelerating the progression of NAFLD.

Keywords: CIH; M1 polarization; Macrophages; NAFLD; OSA; SPP1.