Figure 8.

Adenosine treatment reduces granuloma-associated CKD progression by activating adenosine receptor signaling in macrophages. (A) Schematic of experimental set-up. Alb-creERT2;Glut9^lox/lox mice were injected intraperitoneally with tamoxifen and then fed an acidogenic diet with inosine for 32 days. On day 14, HU+CU mice were injected with adenosine or vehicle every alternate day. (B–D) Serum UA (B) and BUN levels (C), and GFR (D), of adenosine- and vehicle-treated HU+CU mice on days 0–32 (n=5 per group). (E and F) PAS stain (E) illustrates tubular injury and tubular injury score (F) in HU+CU mice on day 14 and in adenosine- and vehicle-treated HU+CU mice on day 32 (n=3–7 mice per group). Magnification, ×100. (G) Number of granulomas on PAS-stained kidney sections (n=3–7 mice per group). (H) Percentage (%) of interstitial fibrosis on silver-stained kidney sections (n=3–7 mice per group). (I–K) Absolute numbers of renal CD45⁺ cells (I), proinflammatory M1-like macrophages (J, CD45⁺MHCII⁺F4/80^hiCD11b⁺CD11c^loCX3CR1⁺CD206⁻), and alternatively activated M2-like macrophages (K, CD45⁺MHCII⁺F4/80^hiCD11b⁺CD11c^loCX3CR1⁺CD206⁺) (n=3–7 mice per group). Data are mean±SD. *P<0.05; **P<0.01; ***P<0.001; NS, not significant by two-way ANOVA. (L) Proposed mechanisms of asymptomatic HU and UA crystalluria. The absence or presence of asymptomatic HU without UA crystalluria does not cause CKD (left panel). Only when UA precipitates in the urine due to a low urinary pH do UA crystals trigger tubular obstruction, inflammation, and interstitial fibrosis, as in chronic UA crystal nephropathy (middle panel). Eventually the crystal plugs translocate into the interstitial compartment. In the interstitium, frustrated phagocytosis of large crystal masses causes the formation of UA crystal granulomas that are composed of M1-like macrophages. These UA crystal granulomas contribute to CKD progression (right panel), which can be inhibited by adenosine.