Janus Kinase 2 Regulates Transcription Factor EB Expression and Autophagy Completion in Glomerular Podocytes

Abstract

The nonreceptor kinase Janus kinase 2 (JAK2) has garnered attention as a promising therapeutic target for the treatment of CKD. However, being ubiquitously expressed in the adult, JAK2 is also likely to be necessary for normal organ function. Here, we investigated the phenotypic effects of JAK2 deficiency. Mice in which JAK2 had been deleted from podocytes exhibited an elevation in urine albumin excretion that was accompanied by increased podocyte autophagosome fractional volume and p62 aggregation, which are indicative of impaired autophagy completion. In cultured podocytes, knockdown of JAK2 similarly impaired autophagy and led to downregulation in the expression of lysosomal genes and decreased activity of the lysosomal enzyme, cathepsin D. Because transcription factor EB (TFEB) has recently emerged as a master regulator of autophagosome-lysosome function, controlling the expression of several of the genes downregulated by JAK2 knockdown, we questioned whether TFEB is regulated by JAK2. In immortalized mouse podocytes, JAK2 knockdown decreased TFEB promoter activity, expression, and nuclear localization. analysis and chromatin immunoprecipitation assays revealed that the downstream mediator of JAK2 signaling STAT1 binds to the TFEB promoter. Finally, overexpression of TFEB in JAK2-deficient podocytes reversed lysosomal dysfunction and restored albumin permselectivity. Collectively, these observations highlight the homeostatic actions of JAK2 in podocytes and the importance of TFEB to autophagosome-lysosome function in these cells. These results also raise the possibility that therapeutically modulating TFEB activity may improve podocyte health in glomerular disease.

Autophagy Function and Regulation in Kidney Disease

“…In podocytes, Jack/Stat signaling facilitates the binding of STAT1 to the TFEB promoter and increases the expression of TFEB, thus, maintaining autophagosome-lysosome function. JACK2-deficient mice in podocytes exhibited impaired autophagy and increased urinary albumin excretion, while mice with TFEB overexpression in JAK2-deficient podocytes had restored autophagosome-lysosome function and albumin permselectivity [181]. These studies suggest that TFEB is a promising therapeutic target for improving podocyte injury in glomerular diseases.…”

Shifts in podocyte histone H3K27me3 regulate mouse and human glomerular disease

“…Under isoflurane anesthesia, the abdominal aorta was cannulated with a 24-gauge angiocath, and the mouse was perfused with 1 × 10 5 Dynabeads in 5 ml HBSS (Thermo Fisher Scientific). Podocytes were isolated using previously reported methods (57,65,66). In brief, glomeruli were seeded on collagen I-coated plates in a 1:1 mixture of F-12 Kaighn's Modification Media (HyClone Laboratories) with media harvested from NIH/3T3 cells (ATCC), and cell cultures were maintained for approximately 4 to 6 days.…”

The Multifaceted Role of the Lysosomal Protease Cathepsins in Kidney Disease

“…A role for CtD in podocytes, responsible for maintaining the ultrafiltration barrier thus preventing urinary protein loss, has also been reported (Yamamoto-Nonaka et al, 2016 ). In a podocyte-specific knock-out mouse model, the absence of CtD resulted in podocyte apoptotic cell death, and in age–dependent, late–onset glomerulosclerosis (Alghamdi et al, 2017 ). Therefore, CtD activity in kidney could be different depending on the cell type, and further studies will be required to clarify this issue.…”