Long non-coding RNA ADPGK-AS1 regulates mitochondrial and metabolic remodeling in macrophages and influences tumor progression

Abstract

Recent immunometabolism studies have shown that alterations in the metabolic profile of macrophages determine the macrophage phenotype and function. Long non-coding RNAs (lncRNAs) regulate macrophage activation and inflammatory gene network, but their role in mitochondrial bioenergetics and metabolism during inflammation and lung cancer progression has been largely unexplored. In this study, we identified lncRNA ADPGK-AS1 in M2-like activated macrophages and tumor associated macrophages (TAMs) to be highly expressed. We found that ADPGK-AS1 can translocate into the mitochondria of macrophages and bind to mitochondrial ribosomal proteins (MRPs), such as MRPL35 and MRPL15. Interaction with the MRPs leads to enhanced number of mitochondria, increased mitochondrial energy production, higher amounts of TCA metabolites fumarate, malate, citrate, and αKG, as well as reduced accumulation of ROS, as seen in ADPGK-AS1 overexpressing macrophages. In addition, in macrophage-tumor-cell crosstalk, ADPGK-AS1 expression was also induced and comparable changes were seen in TCA metabolites. Additionally, we found evidences that ADPGK-AS1 in our co-culture model might be induced by tumor-cell secreted αKG. Notably, ADPGK-AS1 expression modulation and the following alteration in mitochondrial-associated macrophage metabolism was linked to a change in macrophage phenotype. This was observed in (i) in vitro experiments leading to upregulation of inflammatory M1-like markers and downregulation of anti-inflammatory M2-like markers, as well as increased tumor cell apoptosis and decreased tumor cell migration after ADPGK-AS1 knockdown in M2-like macrophages; (ii) in vivo experiments, showing decrease of tumor growth under influence of M2-like macrophages with a ADPGK-AS1 knockdown in NSG mice and (iii) ex vivo experiments leading to a decrease of proliferation and enhanced apoptosis in human tumor precision cut lung slices. Interestingly, MRPL35 was upregulated in ADPGK-AS1 overexpressing macrophages, and the expression pattern of this protein was consistent in all of our models. This suggests that the mitochondrial metabolic regulation of ADPGK-AS1 in macrophages as seen in this study goes via interaction with MRPL35 in the mitochondria. The significance of the present study lies in the exploration of alternative routes for target therapy i.e., knockdown of lncRNA ADPGK-AS1. This influences mitochondrial energy production, thereby causing changes in the macrophage phenotype and finally leading to elevated inflammatory signals and reduced lung tumor growth. The newly discovered pathway constitutes a target for tumor therapy. Thus, targeting ADPGK-AS1 could be a novel approach in treatment of several pathologies associated with macrophage deregulation, particularly lung cancer.