Biomechanical strain mediated maladaptive gene regulation as a contributing factor in Alport glomerular disease

Alport glomerular disease is associated with dysregulation of pro-inflammatory cytokines and matrix metalloproteinases, promoting progressive glomerulonephritis. Changes in composition and structure of Alport GBM resulting from mutations in type IV collagen genes likely alter cell adhesion and cell signaling. Enhanced biomechanical strain on the capillary tuft, resulting from a thinner and less crosslinked GBM may be a source of insult which contributes to gene dysregulation. To test this we subjected cultured podocytes to cyclic biomechanical strain. We observed robust induction of MMP-3, − 9, − 10, and − 14, but not MMP-2 or MMP-12. IL-6 was induced by biomechanical strain, and neutralizing antibodies against IL-6 attenuated induction of MMP-3 and MMP-10. Alport mice given L-NAME salts, which resulted in a significant rise in systolic blood pressure, showed Induction of MMP-3, MMP-10, and IL-6 in glomeruli relative to normotensive Alport mice. Hypertensive Alport mice also had elevated proteinuria, and more advanced GBM disease histologically and ultrastucturally. Collectively these data suggest MMP and cytokine dysregulation may constitute a maladaptive response to biomechanical strain in Alport podocytes, and that this response may contribute to the mechanism of glomerular disease initiation and progression. strain have relied on specialized instruments where cells are plated on elastic membranes which can be stretched precisely using computer assisted programs. These systems have been used extensively in studies of skin, cardiomyocytes, and bone cells, where biomechanical strain would be expected to have important biological consequences. The varied studies have provided a wealth of information regarding how cell adhesion, cytoskeletal dynamics, and cell signaling machinery respond to strained adhesive interactions between cells and extracellular matrix. (8) More recently glomerular podocytes have been studied as a means of understanding how glomerular hypertension contributes to progressive glomerular diseases. These studies noted influences of mechanical strain on maladaptive responses such as activation of the tissue angiotensin system (9) and induction of Secreted Protein Acidic and Rich in Cysteine (SPARC), (10) changes that promote glomeruloschlerosis. Conversely, adaptive responses of podocytes to mechanical strain were also documented, where induction of osteopontin enhances cytoskeletal reorganization and protects against strain-induced podocyte loss. (11) The relevance of these findings was often confirmed in vivo using hypertensive mouse or rat models. (9,10) In this study, we used in vitro and in vivo approaches to examine a potential role for biomechanical strain in regulating expression of matrix metalloproteinases known to contribute to GBM destruction in Alport mouse models. The results suggest that biomechanical strain leads to maladaptive gene regulation in Alport mice, which may constitute an important mechanism for GBM disease initiation and progression. suggesting that the biomechanical influence of hypertension is more pronounced in the Alport mice than wild type mice. We did not observe a statistically significance in lifespan in salt treated versus no-salt Alport mice, likely owing to the accelerated pace of renal disease progression on the 129 Sv/J background.