The role of Krüppel‐like factor 4 in transforming growth factor‐β–induced inflammatory and fibrotic responses in human proximal tubule cells

Abstract

Krüppel-like factor 4 (KLF4) is known to mitigate inflammation in several cell types. Using human proximal tubule cells, the present study aimed to investigate the role of KLF4 in regulating transforming growth factor (TGF)-β₁ induced inflammatory and fibrotic responses. Human kidney proximal tubular cells were exposed to high glucose, or TGF-β₁ and KLF4 expressions were determined. Cells were then transfected with empty vector or KLF4 and exposed to 2-ng/mL TGF-β₁ for up to 72 h. Inflammatory proteins (macrophage migration inhibitory factor and monocyte chemoattractant protein-1) and pro-fibrotic proteins (fibronectin and collagen IV) were measured after 72 h by enzyme-linked immunosorbent assay and western blot, respectively. To determine the relevance to in vivo models of chronic kidney disease, KLF4 protein expression in streptozotocin-induced diabetic mice was determined. Krüppel-like factor 4 messenger RNA (mRNA) levels were significantly reduced in high glucose-treated human kidney proximal tubular cells. High glucose increased TGF-β₁ mRNA expression, which significantly increased migration inhibitory factor and monocyte chemoattractant protein-1 protein secretion. Transforming growth factor-β₁ significantly increased fibronectin and collagen IV protein expression. The overexpression of KLF4 significantly reduced TGF-β-mediated increases in migration inhibitory factor and monocyte chemoattractant protein-1 but had no effect on TGF-β-mediated fibronectin and collagen IV mRNA and protein expression. The levels of KLF4 mRNA were significantly reduced in the diabetic kidney, and diabetic animals had a significant reduction in renal tubular expression of KLF4 proteins. This data suggest that KLF4 reduces inflammation induced by TGF-β₁, suggesting a therapeutic role for KLF4 in diabetic nephropathy.

MicroRNA‐dependent regulation of KLF4 by glucose in vascular smooth muscle

“…Our results suggest that KLF4 is down regulated in smooth muscle cells by hyperglycemia as well as in arteries from diabetic mice and patients. These results are consistent with earlier findings in other tissues including adipose tissue and kidney (Aktug et al, ; Hayashi et al, ; Liao et al, ; Mreich, Chen, Zaky, Pollock, & Saad, ) but in conflict with recent results in smooth muscle (Shyu, Cheng, & Wang, ; Xi, Wai, White, & Clemmons, ). The reason for these discrepancies is not known, but may be due to differences in diabetes models or the time point at which KLF4 expression is analyzed.…”

Krüppel-like factor 4 (KLF4): What we currently know

“…Attenuation of proteinuria by renin-angiotensin blockage was found to be in part via KLF4 suppression (116). In contrast to the proinflammatory role of KLF4 in other systems, KLF4 was shown to reduce inflammation (triggered by TGF-β1) and fibrotic responses, in renal tubular cells during diabetic nephropathy (117). Also, it was recently shown that KLF4 is involved in the regulation of renal physiological functions and the progression of fibrosis (118).…”

The Role of Krüppel-like Factor 4 in Renal Fibrosis

“…In the diabetic kidney, the KLF4 mRNA level is remarkably reduced. In an animal model of diabetic nephropathy, KLF4 expression was significantly decreased in renal tubular cells (Mreich et al, 2015 ). Renal fibrosis is considered to be one of the major pathological changes that occur during the course of diabetic nephropathy (Arora and Singh, 2013 ).…”