Work

Flow is Critical for Maintaining a Protective Phenotype in Renal Proximal Tubular Cells

Year: 2013

Type: article

Abstract: The cessation of blood flow is an immanent component of injury in organ transplantation and ischemia/reperfusion injury. Clinical trials have recently demonstrated benefits of hypothermic pulsatile perfusion during organ preservation supporting the concept that hemodynamic forces play a critical role in initiating organ injury 1. Nevertheless, mechanisms communicating detrimental consequences of stasis in organ preservation remain largely unknown. We have recently proposed that the expression of protective endothelial genes under conditions of pulsatile flow may serve as an explanation 2. The mechano-responsive transcription factor Kruppel-like factor 2 (KLF2) has been shown to play a critical role in integrating an anti-inflammatory, anti-thrombotic endothelial cell phenotype 3. We have previously documented that flow stasis triggers a rapid decay of KLF2 expression leading to acute endothelial dysfunction in conditions of cold storage 4. The absence of flow may thus provide an initial impetus triggering inflammation and injury in organ transplantation. We have now collected in vitro data showing that shear stress is also able to protect tubular epithelial cells, extending our working concept that flow cessation is a critical component of organ injury. In these new experiments, we have exposed human tubular epithelial cells (HK-2) to laminar shear stress. Since tubulitis and tubular necrosis are hallmark lesions in acute kidney injury, and considering that renal proximal tubule cells have been shown to be responsive to biomechanical stimulation 5, we explored phenotypic modifications of tubular epithelial cells relevant to inflammatory processes and tested the secretion of kidney injury molecule-1 (KIM-1) as a surrogate marker for tubular injury. HK-2 cells were exposed to 24 h of physiological laminar shear stress; despite several studies focusing on the transmission of axial flow to modulate fluid reabsorption and alterations of tubule diameter in vitro, specific flow characteristics in the tubule have not been established. We therefore used a flow rate of 1 dyn/cm2 in accordance with previously published data 5 recapitulating physiological conditions. Exposure of HK-2 cells to shear-stress resulted in the up-regulation of KLF2 and a significant reduction in the mRNA expression of adhesion molecules and inflammatory cytokines ICAM-1, VCAM-1, and IL-8. TNF-α mediated up-regulation of VCAM-1, but not of ICAM-1, was muted when the cells were preconditioned with laminar shear stress (Figure 1). Interestingly, the suppression of IL-8 was dependent on the expression of KLF2 (Figure 2). Moreover, exposure of HK-2 cells to laminar shear stress significantly down-regulated mRNA and protein expression of KIM-1 (data not shown). Taken together, our data suggest that shear stress evokes a “tubulo-protective” phenotype in epithelial cells. These observations, although limited to in vitro data at this time, may represent a new conceptual framework for the understanding of tubular injury in the context of renal ischemia with clinical relevance for acute kidney injury and transplantation. The authors of this manuscript have conflicts to disclose according to the American Journal of Transplantation. Marc-Olivier Timsit discloses past and current research grants by AstellasPharma, Institut Georges Lopez / Waters Medical, Novartis and Astra-Zeneca. JVB is co-inventor on patents for KIM-1, which have been assigned to Partners Health Care and licensed to Johnson and Johnson, Genzyme, and Biogen Idec. Other authors have no conflict of interests to disclose. M.-O. Timsit1,2,3*, W. J. Adams1, A. Laguna-Fernandez1, T. Ichimura4, J. V. Bonventre4, G. García-Cardeña1, S. G. Tullius2 1Laboratory for Systems Biology, Department of Pathology, Center for Excellence in Vascular Biology, Harvard Medical School, Boston, Massachusetts 2Division of Transplant Surgery, Harvard Medical School, Boston, Massachusetts 3Université Paris Descartes, Sorbonne Paris Cité, Paris, France 4Renal Division, all, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts * Corresponding author: Marc-Olivier Timsit, [email protected]

Source: American Journal of Transplantation

DOI: 10.1111/ajt.12242