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Abstract: PO1693

Calcium/Calmodulin Kinase 4 Induces FSGS by Promoting Apoptosis While Inhibiting Autophagy in Podocytes

Session Information

Category: Glomerular Diseases

  • 1204 Podocyte Biology

Authors

  • Bhargava, Rhea, Beth Israel Deaconess Medical Center, Boston, Massachusetts, United States
  • Maeda, Kayaho, Beth Israel Deaconess Medical Center, Boston, Massachusetts, United States
  • Satyam, Abhigyan, Beth Israel Deaconess Medical Center, Boston, Massachusetts, United States
  • Stillman, Isaac Ely, Beth Israel Deaconess Medical Center, Boston, Massachusetts, United States
  • Tsokos, George C., Beth Israel Deaconess Medical Center, Boston, Massachusetts, United States
Background

Podocyte injury and death precede the development of focal segmental glomerulosclerosis(FSGS), but the involved mechanisms remain poorly understood. Calcium/calmodulin kinase 4 (CaMK4), a serine threonine kinase, is increased in podocytes of people with FSGS and in mice models of FSGS.

Methods

B6, B6 Camk4.fl/fl.podocincre- or Camk4.fl/fl.podocincre+ mice were created and injected with i.v. adriamycin. Urine was collected on days 0, 3, 7, or 14, and kidney samples were collected on day 7 or 14 after adriamycin injection. Cultured human podocytes in the presence and absence of CAMK4 inhibitor (KN93) were exposed to adriamycin after which immunofluorescence and western blot was performed. Pull down mass-spectrometry and co-immunoprecipitation analysis was performed to identify proteins involved in cell death and those that directly interact with CaMK4 in FSGS.

Results

We found that lack of CaMK4 in podocytes suppressed the development of kidney pathology including the presence of hyaline deposits in glomeruli, podocytopenia and tubulointerstitial damage with intratubular casts in mice injected with adriamycin. Proteinuria in mice lacking CaMK4 in podocytes exposed to adriamycin, was reduced at 7 days and remained low through the 14th day when compared to control mice. Mechanistically we found that CaMK4 phosphorylates 14-3-3, releasing pro-apoptotic protein BAD which in turn binds to the antiapoptotic protein BCL-2, thereby allowing BAX, to aggregate on mitochondria and induce release of cytochrome c through mitochondrial pore formation, followed by caspase activation and apoptosis. In parallel, CaMK4 inhibits autophagy, a process needed for the renewal of damaged organelles, through the mTOR pathway, by directly phosphorylating AKT and S6 kinase.

Conclusion

We demonstrate that mice lacking CaMK4 specifically in podocytes are protected from FSGS-like disease after exposure to adriamycin. These mice also demonstrate markedly reduced proteinuria and podocytopenia. We found that apoptosis leads to cell death while autophagy is protective in FSGS. The characterization of the specific molecular events which lead to podocyte loss and glomerulosclerosis point to putative therapeutic targets and biomarkers for FSGS.

Funding

  • NIDDK Support