Urinary endotrophin predicts disease progression in patients with chronic kidney disease

Abstract

Renal fibrosis is the central pathogenic process in progression of chronic kidney disease (CKD). Collagen type VI (COL VI) is upregulated in renal fibrosis. Endotrophin is released from COL VI and promotes pleiotropic pro-fibrotic effects. Kidney disease severity varies considerably and accurate information regarding CKD progression may improve clinical decisions. We tested the hypothesis that urinary endotrophin derived during COL VI deposition in fibrotic human kidneys is a marker for progression of CKD in the Renal Impairment in Secondary Care (RIISC) cohort, a prospective observational study of 499 CKD patients. Endotrophin localised to areas of increased COL VI deposition in fibrotic kidneys but was not present in histologically normal kidneys. The third and fourth quartiles of urinary endotrophin:creatinine ratio (ECR) were independently associated with one-year disease progression after adjustment for traditional risk factors (OR (95%CI) 3.68 (1.06-12.83) and 8.65 (2.46-30.49), respectively). Addition of ECR quartiles to the model for disease progression increased prediction as seen by an increase in category-free net reclassification improvement (0.45, 95% CI 0.16-0.74, p = 0.002) and integrated discrimination improvement (0.04, 95% CI 0.02-0.06, p < 0.001). ECR was associated with development of end-stage renal disease (ESRD). It is concluded that ECR predicts disease progression of CKD patients.

Figure 1

Histological and immunohistological assessment of tissue sections from control and fibrotic kidneys. The left (A, C, E and A’, C’, E’) and right panel (B, D, F and B’, D’, F’) show representative sections from two paraffin-embedded biopsies of a non-fibrotic kidney and fibrotic kidney, respectively. (A,B) Whereas Masson’s trichrome stain led to a very mild and only focal positivity in the control kidneys, a more intense staining, was observed in the fibrotic kidney. (C) Immunohistochemistry of the non-fibrotic control kidneys using anti-COL VI antibody (αCol6) revealed some staining in the interstitium and surrounding larger blood vessels. (D) The fibrotic kidneys showed noticeable, αCol6 staining in the fibrotic areas, indicating a prominent upregulation of COL VI in fibrosis. (E) Immunohistochemistry of the non-fibrotic kidneys using the anti-Endotrophin antibody (PRO-C6), did not reveal any staining. (F) The fibrotic kidney section showed a clear Endotrophin signal within the fibrotic foci, particularly those with high COL VI content (1D’ and F’). The subfigures labelled with a mark (e.g. A’) are magnifications of the areas outlined with a square. In the fibrotic kidney, the square outlines the same area in subfigures (B, D and F). The scale bars are 250 µm.

Figure 2

ECR correlates with eGFR, one-year relative change in eGFR and albuminuria. Correlation analysis between ECR and (A) baseline eGFR, (B) one-year relative change in eGFR, and (C) ACR are presented. Due to non-normal distribution of data, spearman’s rank correlation analysis was performed. For visualization, all values, except relative change in eGFR, were log-transformed. In each subfigure, spearman’s rho and significance level is shown.

Figure 3

The association of ECR quartiles with one-year disease progression. Odds ratios with 95% CI were plotted for quartiles (Q) of ECR.

Figure 4

Cumulative Kaplan-Meier plot showing development of ESRD by ECR quartile. A table including the number of patients at risk by time has been inserted below the Kaplan-Meier curve. Log-rank significance is inserted in the figure. Q = quartiles.