Abstract: FR-PO374

Thymosin β4 Has Cell-Specific Effects on Renal Fibrosis

Session Information

Category: Chronic Kidney Disease (Non-Dialysis)

  • 308 CKD: Mechanisms of Tubulointerstitial Fibrosis

Authors

  • Zhong, Jianyong, Vanderbilt University Medical Center, Nashville, Tennessee, United States
  • Yang, Jae Won, Wonju Christian Hospital, Wonju, GangWon-Do, Korea (the Republic of)
  • Yang, Haichun, Vanderbilt University Medical Center, Nashville, Tennessee, United States
  • Fogo, Agnes B., Vanderbilt University Medical Center, Nashville, Tennessee, United States
Background


Thymosin β4 (Tβ4) is a G-actin sequestering protein with effects on angiogenesis, cell migration and matrix. We previously showed that Tβ4 is increased in sclerotic glomeruli after 5/6 nephrectomy, but exogenous Tβ4 treatment ameliorated interstitial fibrosis after unilateral ureteral obstruction (UUO). In this study, we investigated the impact on renal fibrosis of Tβ4 knockdown in different cell types.

Methods


Endothelial cell Tβ4 knockdown mice (Tβ4 endo-KD) were generated by mating Tβ4 shRNA loxp mice with SCL Cre mice, with SCL Cre negative mice as control (endo-Cont). We also generated inducible macrophage Tβ4 knockdown mouse (Tβ4 mac-KD) by mating Tβ4 shRNA loxp mice with Lys Cre mice, inducing Tβ4 KD by tamoxifen, with Lys Cre negative mice as control (mac-Cont). Injury was induced by UUO and/or folic acid (FA), with in vitro study of primary macrophages.

Results


In UUO and FA models, Tβ4 endo-KD mice had significantly decreased peritubular capillary density vs control. After UUO at day 14, vascular permeability and interstitial fibrosis were significantly decreased in Tβ4 endo-KD. Endothelial-mesenchymal transition was also decreased in Tβ4 endo-KD vs control. In contrast, in the FA model, Tβ4 endo-KD mice had significantly increased collagen I mRNA, and slower recovery rate of tubular injury, measured by urinary KIM-1/Cr and NGAL/Cr, vs control. The hypoxia markers, HIF1 and HIF2 mRNA levels, were significantly higher in Tβ4 endo-KD mice vs control. Knockdown of Tβ4 in cultured macrophages reduced P-cJun and enhanced Ym-1, although in vivo in UUO, interstitial fibrosis and macrophage infiltration were not different in Tβ4 mac-KD vs control.

Conclusion


We conclude that endothelial cell Tβ4 affects peritubular capillary density and endothelial cell function, while the contribution of endothelial Tβ4 to renal outcome depends on disease model, whether a state of nonreversible interstitial fibrosis vs. toxic acute tubular injury, with beneficial effects of knockdown of Tβ4 in the former, contrasting impaired recovery in the latter. Tβ4 also affects M2 macrophage transition, but knockdown of Tβ4 only in macrophages did not change interstitial fibrosis. We conclude that thymosin b4 has cell and context-specific renal effects.

Funding

  • NIDDK Support