The microRNA-processing enzyme dicer maintains juxtaglomerular cells

Abstract

Juxtaglomerular cells are highly specialized myoepithelioid granulated cells located in the glomerular afferent arterioles. These cells synthesize and release renin, which distinguishes them from other cells. How these cells maintain their identity, restricted localization, and fate is unknown and is fundamental to the control of BP and homeostasis of fluid and electrolytes. Because microRNAs may control cell fate via temporal and spatial gene regulation, we generated mice with a conditional deletion of Dicer, the RNase III endonuclease that produces mature microRNAs in cells of the renin lineage. Deletion of Dicer severely reduced the number of juxtaglomerular cells, decreased expression of the renin genes (Ren1 and Ren2), lowered plasma renin concentration, and decreased BP. As a consequence of the disappearance of renin-producing cells, the kidneys developed striking vascular abnormalities and prominent striped fibrosis. We conclude that microRNAs maintain the renin-producing juxtaglomerular cells and the morphologic integrity and function of the kidney.

Figure 1.

In situ hybridization for miR-145 is shown. (A) Normal expression of miR-145 in JG cells at the entrance to the glomerulus. (B) Expression of miR-145 in JG cells is abolished in Dicer cKO kidneys (arrow). (C) In control mice, miR-145 is expressed throughout the smooth muscle layers of an intrarenal artery. (D) Dicer cKO kidney shows decreased expression of miR-145 in a large vessel. Expression persists in a few cells (arrowhead). (E) Expression of miR-145 along the afferent arteriole of a control kidney. (F) Lack of miR-145 along the afferent arteriole of a Dicer cKO kidney. g, glomerulus. Bar = 100 μm.

Figure 2.

Renin expression and PRC in mice with conditional deletion of Dicer in renin cells are shown. (A) Renin immunostaining. Control mice have the normal endowment of renin-positive cells (brown); however, Dicer cKO mice lack renin-positive cells. *Glomeruli. Bar = 200 μm. (B) qRT-PCR shows reduced levels of both Ren1 and Ren2 renin mRNA in the cKO deletion samples compared with controls. (C) PRC determined by angiotensin I (AngI) generation. Data are means ± SEM. ***P < 0.001, **P < 0.01, *P < 0.05 versus control.

Figure 3.

Arterial BP measurements of Dicer cKO mice are shown. (A) Tail-cuff measurements of systolic BP (SBP) from Dicer^flox/Δ;Ren1^dcre/+ mice. **P < 0.01 versus control (n = 3 per group). (B) Radiotelemetry measurements of mean arterial BP (MAP) from Dicer^flox/flox;Ren1^dcre/+ mice. *P < 0.05 versus control (cKO, n = 6; control, n = 7).

Figure 4.

Masson's trichrome staining of Dicer cKO kidney sections is shown. Interstitial fibrosis is shown by the blue colored staining of the collagen fibers. (Top) Low magnification shows that the mutant kidney is smaller than the control and presents striped fibrosis extending from the cortex to the medulla. (Middle, left) Normal cortex in the control. (Middle, right) A scarred area (striped fibrosis) in the Dicer cKO coincides with the depression of the kidney surface (arrow). (Bottom, left) Interstitial fibrosis involves an artery that has lost its boundaries, and its structure is barely recognizable. (Bottom, right) Area with increased fibrosis shows an abnormal glomerulus with a crescent (arrow) and loss of tubular structures. Bars = 1 mm (top), 200 μm (middle), and 100 μm (bottom).

Figure 5.

Possible mechanisms for the pathogenesis of striped renal fibrosis in Dicer cKO mice are shown.

Figure 6.

Breeding scheme to generate cKO of Dicer in renin cells is shown. (A) Strategy using Dicer^Δ/+ and Dicer^flox/flox mice. An additional control (control 3) with both Dicer alleles intact is not depicted (Dicer^flox/+;Ren1^c+/+). (B) Using Dicer^flox/flox mice, additional genotypes Dicer^flox/flox;Ren1^c+/+, Dicer^+/+;Ren1^c+/+, and Dicer^+/+;Ren1^dcre/cre are not shown.