Abstract Body: We hypothesized that the microbiome modulates glomerular filtration rate (GFR). To test this hypothesis, microbiota was depleted in mice using antibiotics in drinking water (ABX: ampicillin, neomycin, vancomycin). GFR was measured by transcutaneous detection of FITC-sinistrin clearance. GFR was significantly increased after microbiota depletion (ABX) in both sexes (Table 1, Study I). To investigate if the increased GFR was due to the absence of gut microbes, we measured GFR in germ-free (GF) mice, conventional mice (Ctrl), and conventionalized GF mice (CGF, born GF but conventionalized by oral gavage of a fecal slurry from Ctrl mice). GFR was significantly elevated in GF as compared to both control and conventionalized GF mice in both sexes (Table 1, Study II).

To determine if ABX increase GFR in chronic kidney disease (CKD), mice were given adenine or adenine+ABX (simultaneously). Adenine alone decreased GFR. In females, adenine+ABX improved GFR (vs adenine) on weeks 4 and 6. In males, GFR improvement was seen on week 2 (Table 1, Study III). Plasma creatinine was significantly increased on adenine but normalized by ABX treatment in females (chow 0.19 mg/dl ±0.03 vs adenine 0.31±0.02, p=0.04; adenine vs adenine+ABX 0.15±0.03, p=0.005, n=7-9) and males (chow 0.12±0.05 vs adenine 0.34±0.03, p=0.01; adenine vs adenine+ABX 0.17±0.04, p=0.02, n=7-8). Histology revealed that adenine increased collagen; ABX suppressed this increase in both sexes. Adenine also elevated kidney injury molecule (KIM-1, immunostaining) which was mitigated by adenine+ABX. 16S rRNA analysis on female feces indicated that Akkermansia muciniphila was elevated with adenine (vs chow diet), and normalized by adenine+ABX.

We hypothesize that tubuloglomerular feedback (TGF) is involved in microbial regulation of GFR. To test this hypothesis, we used the sodium-glucose cotransporter 2 (SGLT2) inhibitor empagliflozin (EMPA, 62 μg/ml) which impairs Na⁺ reabsorption and thus increases Na⁺ delivery to the macula densa. GFR was significantly increased after ABX treatment at 3 and 5 weeks, the combination of ABX and EMPA resulted in a delayed elevation, suggesting EMPA partially inhibits microbial regulation of GFR (Table 1, Study IV).

In sum, both the absence and suppression of gut microbes increased GFR in healthy mice. Moreover, ABX partially improved kidney function in an adenine-induced CKD model. Further studies indicate microbial regulation of GFR may partially involve changes in TGF.