Podocytes are sensitive to fluid shear stress in vitro

Area of Science:

• Nephrology
• Cell Biology
• Biophysics

Background:

• Podocytes endure mechanical forces from glomerular filtration.
• Stretch impacts podocyte biology and glomerulosclerosis.
• Sensitivity of podocytes to fluid shear stress was previously unknown.

Purpose of the Study:

• To investigate the effects of fluid shear stress on podocytes.
• To determine the threshold of shear stress that affects podocyte viability and structure.
• To elucidate the molecular mechanisms, including cytoskeletal and tyrosine kinase involvement, underlying podocyte response to shear stress.

Main Methods:

• A conditionally immortalized mouse podocyte cell line was exposed to controlled fluid shear stress in a flow chamber.
• Podocyte loss, lamellipodia formation, cytoskeletal organization (actin, cortactin, vinculin), and cell-cell junction integrity (zonula occludens-1, alpha-actinin) were assessed.
• The role of tyrosine kinases (TKs) was evaluated using TK inhibitors (genistein, AG 82).

Main Results:

• Shear stress above 0.25 dyne/cm(2) caused significant podocyte loss, unlike proximal tubular cells.
• Lower shear stress (0.015-0.25 dyne/cm(2)) enhanced lamellipodia formation and redistributed cortactin.
• Stress fibers and focal adhesions were diminished, while cell-cell contacts were reinforced with F-actin and alpha-actinin at higher shear stress.
• Tyrosine kinases were activated and essential for podocyte survival under shear stress, as indicated by increased podocyte loss with TK inhibitors at 0.25 dyne/cm(2).

Conclusions:

• Podocytes exhibit high sensitivity to fluid shear stress.
• Fluid shear stress induces actin cytoskeleton reorganization and activates specific tyrosine kinases in podocytes.
• These responses are critical for podocyte adaptation and survival under mechanical stress in the glomerulus.