Background/Purpose: Infiltrating macrophages are one of the hallmarks of renal inflammation and kidney damage in lupus nephritis. Increasing evidence suggests the crucial role of cell-specific metabolic reprogramming to regulate and modify inflammatory and immune responses. Inflammatory M1-like [TLR4/LPS] macrophages show enhanced glycolysis – which directly drives their inflammatory phenotype – and impaired oxidative phosphorylation (OXPHOS). In contrast, OXPHOS is prominent in tolerogenic M2-like [IL-4] macrophages. Using a systems approach we recently integrated immunologic and molecular profiles of murine LN kidney macrophages with human SLE renal biopsies, identifying shared pathways that link phagocytosis with disposal of excess cellular debris, activation of TLRs and metabolic pathways. Surprisingly, we observed overexpression of TLR8, but not other endosomal TLRs, in these resident renal macrophages. TLR8 overexpression was also detected in lupus nephritis kidneys. TLR8 is expressed primarily by myeloid cells; its role in systemic autoimmunity, and on macrophage immunometabolism, remains elusive as TLR8 function differs from mouse to man. Mice transgenic for multiple copies of human TLR8 develop spontaneous autoimmunity but do not reflect normal physiology. Herein, we aimed to evaluate the functional consequence of one or two copies of human (huTLR8) on macrophage immunometabolism and renal inflammation in murine SLE.

Methods: NZW/B6.Yaa and Sle1.Yaa mice expressing huTLR8 as a BAC transgene (huTR8tg) were generated and followed clinically. HuTLR8 DNA copy number and mRNA expression was confirmed by qDigital and qRT-PCR respectively. 24-week-old huTLR8tg NZW/B6.Yaa mice were administered TL-506 (TLR8-agonist) subcutaneously for 4 weeks and spleen and kidney were harvested for analysis at 8 weeks. Using the Seahorse XF Analyzer, mitochondrial respiration and glycolytic capacity of LPS(TLR4)-, TLR7- and TLR8-stimulated bone marrow-derived macrophages (BMDMs) was assessed.

Results: TL-506-stimulated BMDMs from huTLR8tg mice show enhanced TNF production and glycolysis and impaired mitochondrial respiration compared to wild-type littermates, which was comparable to the profiles observed for LPS- and TLR7-stimulated wt BMDMs. A single copy of huTLR8 in NZW/B6.Yaa mice did not exacerbate/accelerate disease however subcutaneous TLR8-agonist administration appeared to enhance germinal center formation and plasma cell generation in male huTLR8tg mice. To generate lupus mice with 2 copies of huTLR8 we bred the huTLR8tg into the Sle1.Yaa strain. Preliminary findings in these mice show accelerated renal disease and mortality in the males.

Conclusion: One copy of huTLR8 does not seem to exacerbate lupus in NZW/B6.Yaa mice but disease is enhanced by a TLR8 agonist or by the introduction of two copies of the transgene. Interestingly, TLR8-stimulated huTLR8tg BMDMs have a similar immunometabolic profile to LPS-[M1-like] and TLR7-induced macrophages. Further elucidating how TLR8 influences macrophage immunometabolism and phenotype will improve our understanding in how reprogramming macrophage metabolic state might be a potential new avenue of therapeutic targeting in systemic autoimmunity.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-functional-consequence-of-human-hutlr8-on-macrophage-immunometabolism-and-renal-inflammation-in-murine-systemic-lupus-erythematosus/