Cyclosporine A protects podocytes via stabilization of cofilin-1 expression in the unphosphorylated state

Area of Science:

• Nephrology
• Cell Biology
• Pharmacology

Background:

• Nephrotic syndrome involves podocyte foot process effacement, often linked to actin cytoskeleton disruption.
• Cyclosporine A (CsA) shows antiproteinuric effects, potentially independent of T-cell modulation, by stabilizing podocyte actin.
• Previous research suggests CsA stabilizes synaptopodin or directly regulates cofilin-1 in tubular cells, but its role in podocyte cofilin-1 and synaptopodin interaction is unclear.

Purpose of the Study:

• To investigate whether CsA's antiproteinuric effect in podocytes involves regulating cofilin-1.
• To determine if CsA's stabilization of the actin cytoskeleton in podocytes is mediated by cofilin-1, independent of synaptopodin.
• To elucidate the specific molecular targets of CsA in podocytes contributing to the repair of nephrotic syndrome pathology.

Main Methods:

• Puromycin aminonucleoside (PAN)-induced nephrotic rats treated with CsA were analyzed for nephrin, synaptopodin, cofilin-1, and phosphorylated cofilin-1 (pho-cofilin-1) expression and distribution.
• Cultured podocytes exposed to PAN with or without CsA were used to assess CsA's effects on actin cytoskeleton, cofilin-1, and synaptopodin.
• Small interfering RNA (siRNA) was employed to knock down cofilin-1 and/or synaptopodin to evaluate their necessity for CsA's protective effects.

Main Results:

• CsA treatment reduced proteinuria and repaired foot process effacement in PAN-induced nephropathy, restoring key protein expressions in vivo and in vitro.
• CsA demonstrated a capacity to repair the actin cytoskeleton in podocytes damaged by PAN.
• Knockdown of cofilin-1 diminished CsA's protective effect, while synaptopodin knockdown alone did not affect cofilin-1; combined knockdown showed a greater reduction in CsA's benefit than cofilin-1 knockdown alone.

Conclusions:

• The antiproteinuric effect of CsA is primarily attributed to the stabilization of the podocyte actin cytoskeleton through the upregulation of cofilin-1.
• CsA's beneficial action on the actin cytoskeleton and proteinuria is independent of its effect on synaptopodin.
• These findings highlight cofilin-1 as a key mediator of CsA's protective role in podocytes, offering a specific target for therapeutic strategies against nephrotic syndrome.