Inhibiting calpain 1 and 2 in cyclin G associated kinase-knockout mice mitigates podocyte injury

JCI Insight. 2020 Nov 19;5(22):e142740. doi: 10.1172/jci.insight.142740.


Evidence for reduced expression of cyclin G associated kinase (GAK) in glomeruli of patients with chronic kidney disease was observed in the Nephroseq human database, and GAK was found to be associated with the decline in kidney function. To examine the role of GAK, a protein that functions to uncoat clathrin during endocytosis, we generated podocyte-specific Gak-knockout mice (Gak-KO), which developed progressive proteinuria and kidney failure with global glomerulosclerosis. We isolated glomeruli from the mice carrying the mutation to perform messenger RNA profiling and unearthed evidence for dysregulated podocyte calpain protease activity as an important contributor to progressive podocyte damage. Treatment with calpain inhibitor III specifically inhibited calpain-1/-2 activities, mitigated the degree of proteinuria and glomerulosclerosis, and led to a striking increase in survival in the Gak-KO mice. Podocyte-specific deletion of Capns1, essential for calpain-1 and calpain-2 activities, also improved proteinuria and glomerulosclerosis in Gak-KO mice. Increased podocyte calpain activity-mediated proteolysis of IκBα resulted in increased NF-κB p65-induced expression of growth arrest and DNA-damage-inducible 45 beta in the Gak-KO mice. Our results suggest that loss of podocyte-associated Gak induces glomerular injury secondary to calcium dysregulation and aberrant calpain activation, which when inhibited, can provide a protective role.

Keywords: Cell Biology; Chronic kidney disease; Mouse models; Nephrology.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Calpain / antagonists & inhibitors*
  • Diabetic Nephropathies / etiology
  • Diabetic Nephropathies / metabolism
  • Diabetic Nephropathies / pathology
  • Diabetic Nephropathies / therapy
  • Female
  • Glomerulosclerosis, Focal Segmental / etiology
  • Glomerulosclerosis, Focal Segmental / metabolism
  • Glomerulosclerosis, Focal Segmental / pathology
  • Glomerulosclerosis, Focal Segmental / therapy*
  • Humans
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Podocytes / metabolism
  • Podocytes / pathology*
  • Protein Serine-Threonine Kinases / genetics
  • Protein Serine-Threonine Kinases / metabolism*
  • Protein Serine-Threonine Kinases / physiology*
  • Renal Insufficiency, Chronic / etiology
  • Renal Insufficiency, Chronic / metabolism
  • Renal Insufficiency, Chronic / pathology
  • Renal Insufficiency, Chronic / therapy*


  • Intracellular Signaling Peptides and Proteins
  • GAK protein, human
  • GAK protein, mouse
  • Protein Serine-Threonine Kinases
  • Calpain
  • Capn1 protein, mouse
  • Capn2 protein, mouse