AMPK mediates regulation of glomerular volume and podocyte survival

Abstract

We reported that Shroom3 knockdown, via Fyn inhibition, induced albuminuria with foot process effacement (FPE) without glomerulosclerosis (FSGS) or podocytopenia. Interestingly, knockdown mice had reduced podocyte volumes. Human minimal change disease, where podocyte Fyn inactivation was reported, also showed lower glomerular volumes than FSGS. We hypothesized that lower glomerular volume prevented the progression to podocytopenia. To test this hypothesis, we utilized unilateral-and 5/6 th nephrectomy models in Shroom3 knockdown mice. Knockdown mice exhibited less glomerular and podocyte hypertrophy after nephrectomy. FYNknockdown podocytes had similar reductions in podocyte volume, implying Fyn was downstream of Shroom3.Using SHROOM3-or FYN-knockdown, we confirmed reduced podocyte protein content, along with significantly increased phosphorylated AMP-kinase, a negative regulator of anabolism. AMP-Kinase activation resulted from increased cytoplasmic redistribution of LKB1 in podocytes. Inhibition of AMP-Kinase abolished the reduction in glomerular volume and induced podocytopenia in mice with FPE, suggesting a protective role for AMP-Kinase activation. In agreement with this, treatment of glomerular injury models with AMP-Kinase activators restricted glomerular volume, podocytopenia and progression to FSGS. Glomerular transcriptomes from MCD biopsies also showed significant enrichment of Fyn-inactivation and Ampk-activation vs FSGS glomeruli. In summary, we demonstrate the important role of AMP-Kinase in glomerular volume regulation and podocyte survival. Our data suggest that AMP-Kinase activation adaptively regulates glomerular volume to prevent podocytopenia in the context of podocyte injury.

The Pathology Lesion Patterns of Podocytopathies: How and why?

“…During the progression from MC to FSGS lesion, the glomeruli significantly increase their volumes and podocyte hypertrophy appears as a distinguishing feature of FSGS vs. MC ( Fogo et al, 1990 ). This would suggest that interventions aimed at regulating glomerular volume and podocyte hypertrophy could represent an effective strategy to sustain podocyte survival and to prevent podocytopenia ( Puelles et al, 2019 ; Banu et al, 2021 ). However, this adaptive response of podocytes is only sustainable until a threshold is reached, after which the podocyte detaches and progression to FSGS occurs.…”

Comparative evaluation of glomerular morphometric techniques reveals differential technical artefacts between FSGS and normal glomeruli

“…We also recently reported increased MGV in mice models with FSGS compared to the respective controls in each model 10 . Here we re-evaluated this data given the contribution of reduced shrinkage artefact seen in FSGS glomeruli to the reported glomerulomegaly reported in FSGS.…”

“…To evaluate morphometry during significant glomerular injury, we used mice from two FSGS models performed in BALBc/J (n=10) - hypertrophic injury and a previously published ageing model [See methods 10,17 ]. The mice in these FSGS models had confirmed podocyte loss, glomerulosclerosis, proteinuria and azotemia 10,17 . In each animal, we evaluated three plastic-based morphometric techniques and three paraffin-based methods, comparing each with Vglom-Cav.…”

“…We used young male adult BALBc/J as controls (2-6 months age) for evaluating baseline morphometry (n=10). To evaluate morphometry with significant glomerular injury, we used mice from two FSGS models which were also performed in BALBc/J background(n=10) - hypertrophic injury and a previously published ageing model 10,17 . The FSGS lesions in these mice models were confirmed and characterized by a renal pathologist [representative images in Supplementary Figure].…”

“…Quantitative glomerular structural evaluation by morphometry has consistently revealed additional prognostic benefit over histology in human or experimental, diabetic-1,2 , or non-diabetic-glomerular disease [2][3][4][5][6][7][8][9] . For instance, we and others reported that FSGS was associated with larger glomerular volumes (Vglom) and podocyte hypertrophy, and that larger Vgloms predicted outcomes in human nephrotic syndromes 4,10 . Pathophysiologically, Vglom may reflect antecedent nephron injury and loss, with the consequent need for remaining nephrons (and glomeruli) to hypertrophy to increase the effective filtration surface area.…”