The antifibrotic potential of transglutaminase 2 inhibition beyond TGFβ1 release in human kidney tissue and isolated cell cultures

AIMS: The open conformation of the enzyme transglutaminase 2 (TG2) contributes to kidney fibrosis through transamidase activity by cross-linking extracellular matrix fibres and releasing transforming growth factor β1 (TGFβ1), a key driver of fibrogenesis. We investigated the antifibrotic potential of TG2 inhibition downstream of TGFβ1 using two TG2 inhibitors, LDN27219 and Z-DON, which modulate TG2 into the closed and open state, respectively. MATERIALS AND METHODS: The TG2 inhibitors were studied in human precision-cut kidney slices (PCKS) and in cell cultures of primary renal cell types: endothelial and epithelial cells, and fibroblasts. PCKS and cell cultures were stimulated with TGFβ1 (10 ng/ml) for 48 h with or without LDN27219 (10 μmol/l) or Z-DON (40 μmol/l). We evaluated mRNA and protein expression of TG2 and fibrosis markers (fibronectin, α-smooth muscle actin and collagens), and TG2 transamidase activity. KEY FINDINGS: In PCKS, TG2 was unaffected by TGFβ1, but mRNA levels of fibrosis markers increased with the stimulation and decreased in most LDN27219-treated PCKS compared to the control. No changes in protein expression of fibrosis markers were achieved with TGFβ1. In endothelial and epithelial cells, but not fibroblasts, fibronectin expression was increased with TG2 inhibition. Conversely, collagen 3α1 decreased by TG2 inhibition, further amplified by the closed conformation. SIGNIFICANCE: The antifibrotic effects of TG2 inhibition extend beyond the release of TGFβ1, specifically in the closed conformation, although this varies among cell types. Our results indicate that the closed conformation of TG2 has an active antifibrotic potential in humans, in addition to blocking transamidase activity.