COLLAPSING GLOMERULOPATHY DRIVEN BY ABERRANT ACTIVATION OF ERK1/2

Collapsing glomerulopathy is associated with a poor prognosis, its pathophysiology remains inadequately understood, and available treatment options are limited. Phosphorylation of ERK1/2 (p-ERK1/2) has been suggested to play a role in podocyte injury; however, previous evidence originates from in vitro studies, leaving the role of p-ERK1/2 in podocytes in vivo insufficiently elucidated.

We examined the expression of p-ERK1/2 in podocytes in human kidney diseases and mouse experimental models of podocyte injury. Next, we established transgenic mice and cell lines in which ERK1/2 is constitutively phosphorylated in a doxycycline-dependent manner, specifically within podocytes. Furthermore, to investigate gene alterations associated with ERK1/2 phosphorylation in podocytes, we conducted podocyte-specific spatial transcriptomic analysis using photo-isolation chemistry (PIC) in transgenic mice, in addition to comprehensive transcriptomic analysis of the cell lines. 

p-ERK1/2-positive podocytes were observed across various human kidney diseases, including diabetic kidney disease, hypertensive nephrosclerosis, and IgA nephropathy, with the highest prevalence noted in collapsing glomerulopathy. Similarly, in wild-type mice, p-ERK1/2 was identified in a subset of podocytes with aging and in the adriamycin-induced nephropathy model. Transgenic mice that constitutively expressed p-ERK1/2 in podocytes developed progressive proteinuria and kidney dysfunction. Histological examination revealed significant podocyte hypertrophy, cytoplasmic vacuolization, foot process effacement, and sequential podocyte detachment, which are highly reminiscent of human collapsing glomerulopathy. Immunohistochemical staining revealed decreased expression of podocyte markers, and numerous detached podocytes observed in the tubular lumen. TUNEL staining revealed no evidence of cell death in podocytes, either in those remaining on the glomerular tuft or those detached into the tubules. PIC RNA-seq analysis revealed that ERK1/2 activation in podocytes significantly altered the expression of genes associated with cell motility, focal adhesion, and actin filament organization. Podocyte cell lines constitutively expressing p-ERK1/2 showed enhanced cell motility, actin cytoskeleton remodeling and a reduced number of focal adhesions, corroborating the in vivo findings. RNA-seq analysis of these cell lines further revealed enhanced gene expression associated with cell motility and focal adhesion, similar to the in vivo PIC RNA-seq results, as well as increased ribosome biogenesis, suggesting the involvement of enhanced protein synthesis in podocyte hypertrophy observed in vivo.

We found that phosphorylation of ERK1/2 in podocytes induces alterations in cellular structure and function, facilitating increased motility and reduced adhesion, ultimately leading to podocyte detachment. Combined with strong ERK1/2 phosphorylation in podocytes in human collapsing glomerulopathy, these processes may contribute to the pathogenesis of this disease. Our findings underscore the role of ERK1/2 signaling as a pivotal mediator of podocyte pathology and suggest it as a potential therapeutic target for glomerular diseases characterized by podocyte injury and loss.

This work was first presented at ASN Kidney Week 2025, and re-submission is permitted by ASN.