Urinary Mitochondrial DNA Induces an Inflammatory Response in Peripheral Blood Mononuclear Cells

Background: Mitochondria are semiautonomous cell organelles having its own nucleic acid. Mitochondrial DNA (Mt-DNA) remain in hypomethylated (CpG) state and impose an immunogenic response by binding to the toll-like receptor (TLR-9) through the NF-kB pathway. Innate immune cells recognize the hypomethylated pattern of mt-DNA and quickly trigger the innate immune response. The immunomodulatory effects of urinary mt-DNA derived from renal transplant recipients with COVID-19-associated acute kidney injury (AKI) have not been studied. Materials and Methods: Healthy donor peripheral blood mononuclear cell (PBMC) was cultured with the urinary Mt-DNA derived from the renal transplant recipients, who previously developed SARS-CoV-2 infection associated AKI. Cell activation was measured by the flow cytometry. In cell pellets, interleukin IL-6, IL-10, and Myd88, TLR-9 mRNA transcript expression was measured by the reverse transcription polymerase chain reaction. The IL-6 and IL-10 cytokine levels were measured by the enzyme-linked immunosorbent assay in culture supernatants. Results: The urinary mitochondrial DNA (umt-DNA) significantly induces the activation of > 75% of PBMCs. The m-RNA transcript expression of the inflammatory gene in control versus umt-DNA treated PBMCs was for IL-6 (0.99 +/- 0.05 vs. 2.18 +/- 1.15 au; P = 0.004), MYD88 was (1.00 +/- 0.05 vs. 1.55 +/- 0.31; P < 0.001), TLR-9 (1.00 +/- 0.05 vs. 3.33 +/- 1.37 au; P < 0.001) was upregulated, and the IL-10 (1.00 +/- 0.13 vs. -1.73 +/- 0.58; P < 0.001) level was downregulated. However, in PBMC culture supernatants, IL-6 level in control versus umt-DNA-treated groups were (37.50 +/- 13.79 vs. 186.9 +/- 15.50 pg/mL; P < 0.001), which was significantly higher in umt-DNA-treated groups and the IL-10 (8.80 +/- 2.16 vs. 7.60 +/- 3.12 pg/mL; P = 0.32) level was similar between the control- and umt-DNA-treated groups. Conclusions: Urinary Mt-DNA significantly induces the inflammatory cytokine IL-6 secretion from the PBMCs through the Myd88-dependent pathway.