Kidney Week

Abstract: TH-OR019

Smad Anchor for Receptor Activation (SARA) Prevents Pericyte Activation and Protects Kidney from Fibrosis

Session Information

• CKD: Mechanisms of Kidney Fibrosis
  October 25, 2018 | Location: 9, San Diego Convention Center
  Abstract Time: 06:06 PM - 06:18 PM

Category: CKD (Non-Dialysis)

• 1903 CKD (Non-Dialysis): Mechanisms

Authors

• Liang, Xiaoyan, Northwestern University, Chicago, Illinois, United States

Xiaoyan Liang

• Schnaper, H. William, Northwestern University, Chicago, Illinois, United States

H. William Schnaper,

• Humphreys, Benjamin D., Washington University School of Medicine, Clayton, Missouri, United States

Benjamin D. Humphreys,

• Hayashida, Tomoko, Northwestern University, Chicago, Illinois, United States

Tomoko Hayashida,

Background

Pericytes are a major source of fibrogenic cells in injured kidneys. We previously reported that decreasing SARA expression drives cultured proximal tubular epithelial cell dedifferentiation to a pro-fibrotic phenotype, and last year at ASN showed that pericyte-specific overexpression of SARA prevents interstitial fibrosis induced by aristolochic acid (AA) in mice. Here, we characterize the actions of SARA in pericytes.

Methods

Conditional human SARA-overexpressing mice were bred with PDGFRβ-Cre mice to drive pericyte SARA expression. The offspring were further bred with Z/EGFP or COL1A1-GFP mice to mark cells where Cre or type I collagen transcription is active, respectively. Mice were given AA (2.5 mg/kg, i.p., 3x week, for 3 weeks), then sacrificed after 3 more weeks. Harvested kidneys were enzymatically digested and sorted for GFP⁺ cells to obtain pericytes that were analyzed by flow cytometry and qPCR. A pericyte line (Gli1⁺-iPeri) was isolated from a Gli1⁺ tdTomato Immortomouse.

Results

As anticipated, native SARA mRNA expression was 62% decreased after AA treatment in GFP⁺ cells isolated from both phenotypically wild-type (SARA^WT; PDGFRβ-Cre⁺; Z/EGFP) and SARA-overexpressing (SARA^Tg; PDGFRβ-Cre⁺; Z/EGFP) mice. Transgene-derived SARA was detected even after AA, only in SARA^Tg mice. SARA^Wt mice showed significant expansion of the renal interstitial, GFP⁺ pericyte population after AA treatment, but this did not occur in mice with SARA-overexpression in pericytes. GFP⁺ cells isolated from wild-type mice without AA were NG2⁺, CD90.1^-, confirming their pericyte origin. AA treatment induced 45% of the wild-type GFP⁺ cells to become CD90.1⁺, suggesting pericyte fibroblastic transition. This shift was not observed in GFP⁺ cells isolated from AA-treated, SARA-overexpressing mice. COL1A1 mRNA expression was incrased by 10 fold in GFP⁺ cells from SARA^Wt but not SARA^Tg littermates. The Gli1⁺-iPeri cell line expressed very little SARA in culture and strongly expressed αSMA. However, transfection with SARA significantly reduced TGF-β1-induced αSMA and COL1A2 promoter activity, suggesting that re-introduction of SARA at least partially reverses the fibrotic nature of Gli1⁺-iPeri cells.

Conclusion

These data suggest that SARA expression in pericytes suppresses their activation to produce extracellular matrix.

Funding

• NIDDK Support