Bariatric Surgery Modulates Urinary Levels of MicroRNAs Involved in the Regulation of Renal Function

Abstract

Background: Obesity and diabetes cause chronic kidney disease with a common pathophysiology that is characterized by the accumulation of collagen in the extracellular matrix. Recent evidence has implicated the epithelial-to-mesenchymal transition (EMT) as a key step in this pathology with regulation by microRNAs. Weight loss leads to improvements in renal function; therefore, this study hypothesized that bariatric-surgery aided weight loss would lead to changes in urinary microRNAs involved in the regulation of renal function. Materials and methods: Twenty-four bariatric patients undergoing Roux-en-Y gastric bypass and sleeve gastrectomy donated urine pre-operatively and at 2-6 months and 1-2 years post-operatively. Urine samples were also obtained from 10 healthy weight and 7 morbidly obese non-surgical controls. Expression levels of kidney microRNAs were assessed in urine and the function of microRNAs was assessed through the in vitro transfection of HK-2 cells, a kidney proximal tubule cell line. Results: Levels of miR 192, miR 200a, and miR 200b were upregulated in urine following bariatric surgery. This increase was consistent across surgical type and diabetes status and was maintained and enhanced with time. Bariatric surgery alters urinary miR 192 expression from levels seen in morbidly obese patients to levels seen in healthy weight control patients. In mechanistic studies, the transfection of miR 192 in HK-2 cells increased miR 200a expression and decreased ZEB2, a key transcriptional promoter of kidney fibrosis. Conclusions: Bariatric surgery increased miR 192 and miR 200 urinary levels, key anti-fibrotic microRNAs that could contribute to a renal-protective mechanism and may be of value as urinary biomarkers following surgery. These findings suggest that urinary microRNAs may represent potential novel biomarkers for obesity-associated renal function.

Keywords: bariatric/metabolic surgery; diabetes; longitudinal; microRNA; nephropathy; urinary.

Figure 1

Clinical measurements. Pre-operative, post-operative, and control levels of (A) BMI, (B) fasting blood glucose levels and (C) eGFR. Data represent mean ± SEM. ^*p < 0.05, ^****p < 0.0001 by Student's t-test.

Figure 2

Urinary miR 192 expression following bariatric surgery. (A) RYGB patients. (B) Sleeve gastrectomy patients. (C) Patients with diabetes. (D) Patients without diabetes. Data represents mean fold change ± SEM relative to mean preoperative expression. n = 20 for RYGB, n = 4 for sleeve, n = 9 for diabetes, and n = 15 for individuals without diabetes. Each patient is represented by a unique symbol. ^*p < 0.05 vs. preoperative expression by paired t-test.

Figure 3

Bariatric urinary miR 192 expression relative to a morbidly obese cohort. (A) Bariatric and healthy weight miR 192 expression relative to a morbidly obese control group. Data represents mean ± SEM relative to mean preoperative expression. Morbidly obese is a BMI ≥ 40 kg/m², healthy weight is a BMI < 25 kg/m². n = 7 for morbidly obese, n = 10 healthy weight, n = 24 for preoperatively, 2–6 months and 1–2 years post-operatively. (B) Pearson correlation of miR 192-fold change against change in post-operative BMI. n = 46. (C) Timecourse of miR 192 expression following surgery. Data represented as fold change relative to individual preoperative expression for 24 bariatric patients.

Figure 4

Urinary expression of miR 200 following bariatric surgery. (A) miR-200a, n = 9 (B) miR-200b, n = 8. Data represents mean fold change ± SEM relative to mean preoperative expression. ^**p < 0.01 vs. preoperative expression by paired t-test. Each patient is represented by a unique symbol. Timecourse of (C) miR 200a and (D) miR 200b expression following surgery. Data represented as fold change relative to individual preoperative expression.

Figure 5

miR 192 mimic transfection of HK2 cells illustrates its anti-fibrotic role. Expression of (A) miR 192 (B) miR 200a (C) ZEB1 (D) ZEB2 and (E) Colα1 following 48 h of 10, 20, and 50 nM miR 192 mimic transfection. Data represents mean ± SEM relative to transfection with a scrambled control. ^*p < 0.05, ^***p < 0.001, ^****p < 0.0001, n = 3.

Figure 6

The renal function of miR 192 and miR 200. (Left) Mechanism for glucose-mediated renal fibrosis in the proximal tubular cells. Diabetes increases TGF-β which inhibits miR 192/200, lifting the suppression on ZEB and EMT. (Right) Suggested mechanism following bariatric surgery.