Metabolism and B lymphocytes: effects of caloric restriction on the mitochondrial dynamics of B-1 cells

• Grant number: 21/03192-4
• Support type: Scholarships in Brazil - Doctorate
• Effective date (Start): August 01, 2021
• Effective date (End): May 31, 2025
• Field of knowledge: Biological Sciences - Immunology - Cellular Immunology
• Principal researcher: Niels Olsen Saraiva Câmara
• Grantee: Luísa Menezes Silva
• Home Institution: Instituto de Ciências Biomédicas (ICB). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Caloric Restriction (CR) is one dietary intervention that promotes longevity. Among several factors that contribute to its benefits, one is the decrease in fat deposits, which slows down several physiological and metabolic changes. However, little is known about the beneficial effects induced by CR in immune cells residing in adipose tissue, especially B cells. B-1 cells, or innate-like B cells, are present in large amounts in the visceral fat deposits and in the peritoneal/pleural cavities, and that the proportion of B-1 and B-2 cells in the adipose tissue can define the local inflammatory condition. In addition, B-1 cells are known to have increased metabolic demand in relation to other subtypes of lymphocytes, such as B-2 cells and T lymphocytes. However, it is not known how caloric deprivation impacts metabolism and, consequently, the functionality of these cells. Our hypothesis is that CR directly interferes with the mitochondrial dynamics of B-1 cells residing in the Visceral Adipose Tissue (VAT) and Peritoneal Cavity (PC), increasing the uptake and storage of lipids in these cells and supporting their oxidative metabolism, which it does not occur in B-2 cells. To confirm our hypothesis, we will submit C57BL/6 mice to CR and to more directly assess the effects on mitochondrial dynamics, Mfn2flox/flox or CD19cre Mfn2flox/flox mice will be submitted to the same dietary protocol. The animals will be restricted of 40% of the amount consumed by the control group ad libitum, for 4 weeks. Next, we will evaluate how CR affects the dynamics of B cell populations in the VAT and CP of these animals, by flow cytometry. In addition, CD19+ CD23neg CD5+ (B-1a) and CD19+ CD23neg CD5neg (B-1b) cells obtained from VAT and PC of animals ad libitum or under RC, will be isolated by cell sorting and metabolically evaluated by extracellular flow assay (Seahorse). The morphological profile of the mitochondria will be accessed by electron microscopy. We will also evaluate signaling pathways that regulate metabolism, including the expression of proteins related to mitochondrial function, Ca2+ homeostasis, and autophagy. We want to understand how the signaling via CXCR5 relates to changes in mitochondrial dynamics during CR since B-1 cells have a large amount of this chemokine receptor and signaling via CXCL13 seems to be closely associated with the activation of PI3K/Akt/mTOR and MAPK/ERK. To confirm whether changes in mitochondrial dynamics can be mediated by signaling via CXCL13/CXCR5, we will transfer B-1 cells with CXCR5 deletion (-/-) to animals with deficient functional B cells (RAG1 KO) and submit these animals to CR. We will also access the direct changes in the metabolism of these B-1 cells ex vivo, evaluating the same parameters. We believe that CR exerts changes in the mitochondrial dynamics of B-1 cells, which can be mediated by the CXCL13/CXCR5 pathway, and that this metabolic reprogramming will directly interfere with its activation, proliferation, and production of antibodies. Understanding additional mechanisms on how CR exerts its beneficial effects on the immune system will enable the emergence of new therapeutic targets for the control of inflammatory processes. (AU)