The transcriptional repressor Krüppel-like Factor 3 (KLF3) is an important regulator of gene expression in red blood cells and B cells. KLF3 has also been shown to regulate metabolism in white adipose tissue. KLF3 knockout mice are lean due to fewer and smaller adipocytes in smaller fat pads and are protected from high fat diet induced obesity and glucose intolerance. In order to understand how KLF3 deficiency alters metabolism we sought to identify direct target genes of KLF3 in adipose tissue. Lgals3 emerged as such a candidate from expression arrays.

The Lgals3 gene encodes the β-galactoside-binding protein, galectin-3. Galectin-3 has been implicated in a broad range of biological processes, from chemotaxis and inflammation to fibrosis and apoptosis. Galectin-3 has been identified as an important regulator of inflammation in metabolic tissue and is highly expressed in macrophages. Its deficiency in mice is associated with increased adiposity, systemic inflammation and an accumulation of inflammatory cells in metabolic tissue. Thus, galectin-3 is thought to serve as a protective factor in obesity and other metabolic disorders. Despite considerable interest in galectin-3, little is known about its physiological regulation at the transcriptional level.

In this study, using KLF3 knockout mice, chromatin immunoprecipitations, cellular and molecular analyses we show that KLF3 directly represses galectin-3 transcription. Galectin-3 is broadly upregulated at the RNA and protein levels in KLF3-deficient mouse tissues, including white adipose tissue and macrophages. KLF3-deficient adipose tissue secretes more galectin-3 and, within white adipose tissue, both the adipocytes and stromal vascular compartments show higher Lgals3 expression by immunohistochemistry and qPCR. KLF3 occupies regulatory regions of the Lgals3 gene in vivo and directly binds its cognate elements (CACCC boxes) in the galectin-3 promoter in vitro. KLF3 directly represses Lgals3 activation in cellular reporter assays. We also provide mechanistic insight into the regulation of Lgals3, demonstrating that C-terminal binding protein (CtBP) is required to drive optimal KLF3-mediated silencing.

These findings help to enhance our understanding of how expression of the inflammatory modulator galectin-3 is controlled, opening up avenues for potential therapeutic interventions in the future. Our discovery that KLF3 regulates the expression of an important macrophage gene has also prompted our investigation of the importance of KLF3 in innate immune cells that reside in metabolic tissues, such as macrophages, and how such a role may contribute to the metabolic regulatory function of KLF3 in vivo.