Gut microbes regulate glomerular filtration rate in health and in a model of chronic kidney disease
Authors: Xu Jiaojiao , Verma Eesha , Sanchez Jason , Gharaie Sepideh , Gupta Kunal , Rabb Hamid , Pluznick Jennifer L. 
Published: May 2024

Gut microbes have been implicated in varied physiological and pathophysiological processes. In this study, we hypothesized that gut microbes modulate glomerular filtration rate (GFR). Gut microbiota was depleted using a modified antibiotic (ABX) treatment protocol with a mixture of 1g/L ampicillin, 1g/L neomycin, and 0.5 g/L vancomycin (modified from Rakoff-Nahoum et al. 2004). C57BL/6J male and female mice (6-weeks-old) were treated with ABX in drinking water for five weeks. Bacteria reduction with ABX treatment was confirmed by qPCR of fecal samples using pan-bacterial primers (Ct value for Females, F: ctrl 13±0.18 vs ABX 21±0.41; Males, M: 13±0.11 vs ABX 20±0.44, n=8). GFR measurements were performed in conscious and unrestrained mice by transcutaneous detection of fluorescent FITC-sinistrin. The GFR was significantly increased in ABX-treated mice (F: ctrl 1190±14 vs ABX 1638±21, p=0.03; M: ctrl 1020±25 vs ABX 1381±29, p=0.005, n=8). To investigate if the increased GFR was due to the absence of gut microbiota, we measured GFR in germ-free (GF) mice (born and raised without gut microbes), conventional mice (Ctrl, born with gut microbes), and conventionalized GF mice (CGF, born without gut microbes but given a fecal slurry containing gut microbes by oral gavage). GFR was increased in GF mice (F: 1853±32, p=0.003; M: 1308±16, p=0.02) versus both conventional (F: 1217±17; M: 1087±18) and CGF (F: 1326±31, p=0.02; M: 1101±10, p=0.03, n=7-8). GFR was similar in Ctrl and CGF mice. To further investigate if ABX can increase GFR in chronic kidney disease (CKD) when GFR is impaired, GFR was measured in adenine-induced CKD. Adenine (in food pellets) and ABX (in drinking water) treatments were begun simultaneously; adenine decreased GFR in females at weeks 4 and 6, and in males at weeks 2, 4 and 6. In females, mice co-treated with ABX and adenine had increased GFR on week 4 (chow: 1298±11 vs adenine: 853±8, p<0.0001; adenine vs adenine+ABX: 1040±9, p=0.04) but not week 6 (chow: 1238±21 vs adenine: 618±9, p=0.0001; adenine vs adenine+ABX: 881±14, p=0.09, n=7-9). Of note, GFR exhibited no difference between chow vs adenine (data not shown) on week 2. In males, ABX increased GFR on week 2 (chow: 1116±31 vs adenine: 913±47, p=0.002; adenine vs adenine+ABX: 1150±49, p=0.0003) but not week 4 (chow: 1154±38 vs adenine: 732±58, p<0.0001; adenine vs adenine+ABX: 877±81, p=0.37) or 6 (chow: 1157±43 vs adenine: 513±51, p<0.0001; adenine vs adenine+ABX: 591±50, p=0.56, n=7-9). To explore the mechanism by which ABX increase GFR we tested the hypothesis that, in the absence of gut microbes, proximal tubular Na+ reabsorption increases, leading to a reduced Na+ delivery to the macula densa and altering tubuloglomerular feedback (TGF) to increase GFR. To test this, we used the sodium-glucose cotransporter 2 (SGLT2) inhibitor empagliflozin (EMPA) to impair Na+ reabsorption and increase Na+ delivery to the macula densa. As seen previously, treatment with ABX increased GFR on week 3 (F: 1430±13, p=0.04; M:1341±9, p=0.01) and week 5 (F: 1857±21, p=0.002, M: 1443±10, p=0.0001) compared to before treatment (F: 1140±10, M: 1090±11, n=8-9). Co-treatment of EMPA and ABX impaired GFR increases on week 3 (F: 1281±18, p=0.9, M: 1201±11, p=0.9) but not week 5 (F: 1650±21, p=0.01; M: 1281±20, p=0.003) when comparing to before the treatment (F: 1199±15; M: 1109±8, n=8-9). In this study, both the absence (GF) and suppression (ABX) of gut microbes increased GFR in healthy females and males. Moreover, ABX partially restored GFR in adenine-induced CKD females and males. These data suggest that gut microbes influence GFR in both health and disease, and that the mechanism may partially involve TGF. AHA Career Development Award (JX) and NIDDK Diabetic Complications Consortium (RRID:SCR_001415m www.diacomp.org, grants DK076169 and DK 115255 (subaward to JLP)) and American Heart Association Established Investigator Award (to JLP). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.