Glucocorticoid receptors expression and histopathological types in children with nephrotic syndrome

Glucocorticoid receptors and their upstream epigenetic regulators in adults with steroid-resistant nephrotic syndrome

Steroid-resistant nephrotic syndrome (SRNS) is a clinical challenge with variable clinical outcomes. In patients with SRNS, unsuccessful anti-inflammatory and anti-proteinuric effects of steroids lead to end-stage renal disease (ESRD). Our objective was to define the expression pattern of the glucocorticoid receptors (GR) α and β and their epigenetic regulators (miR-24, miR-30a, and miR-370) in a group of adults with SRNS. In this regard, sixty primary NS patients with focal segmental glomerulosclerosis (FSGS, N = 30) and membranous glomerulonephritis (MGN, N = 30) and also healthy volunteers (N = 24) were enrolled. Real-time PCR was performed to evaluate the expression levels of the aforementioned genes in peripheral blood mononuclear cell (PBMC) samples. Furthermore, an in-silico analysis was performed to understand the signaling pathways and biological procedures that may be targeted by these microRNAs in NS. The decreased and increased levels of GRα and GRβ were not significant, respectively. Statistically significant reduced miR-24 levels were observed between control/MGN (p = .022) and MGN/FSGS (p = .032) groups. Additionally, a decrease was detected in miR-30a between MGN and FSGS (p = .049) groups. There was a significant increase in miR-370 expression level between control and NS groups (p = .029), as well as control/MGN (p = .008), and MGN/FSGS (p = .046). Bioinformatics analysis predicted the possible targets of the studied genes including genes involved in TGF-β, Notch1, and p53 signaling pathways, regulation of gene expression, intracellular signal transduction, negative regulation of response to the stimulus, cell-cell signaling, and cell activation in the pathogenesis of SRNS. Taken all together, dysregulated levels of GRα, GRβ were not attributed to SRNS in our patients. It seems that pharmacokinetics and the genetic variations in podocyte-related genes may be associated with the steroid-resistance in our adult patients with NS rather than GR expression.

α Actinin 4 (ACTN4) Regulates Glucocorticoid Receptor-mediated Transactivation and Transrepression in Podocytes

Glucocorticoids are a general class of steroids that possess renoprotective activity in glomeruli through their interaction with the glucocorticoid receptor. However, the mechanisms by which glucocorticoids ameliorate proteinuria and glomerular disease are not well understood. In this study, we demonstrated that α actinin 4 (ACTN4), an actin-cross-linking protein known to coordinate cytoskeletal organization, interacts with the glucocorticoid receptor (GR) in the nucleus of human podocytes (HPCs), a key cell type in the glomerulus critical for kidney filtration function. The GR-ACTN4 complex enhances glucocorticoid response element (GRE)-driven reporter activity. Stable knockdown of ACTN4 by shRNA in HPCs significantly reduces dexamethasone-mediated induction of GR target genes and GRE-driven reporter activity without disrupting dexamethasone-induced nuclear translocation of GR. Synonymous mutations or protein expression losses in ACTN4 are associated with kidney diseases, including focal segmental glomerulosclerosis, characterized by proteinuria and podocyte injury. We found that focal segmental glomerulosclerosis-linked ACTN4 mutants lose their ability to bind liganded GR and support GRE-mediated transcriptional activity. Mechanistically, GR and ACTN4 interact in the nucleus of HPCs. Furthermore, disruption of the LXXLL nuclear receptor-interacting motif present in ACTN4 results in reduced GR interaction and dexamethasone-mediated transactivation of a GRE reporter while still maintaining its actin-binding activity. In contrast, an ACTN4 isoform, ACTN4 (Iso), that loses its actin-binding domain is still capable of potentiating a GRE reporter. Dexamethasone induces the recruitment of ACTN4 and GR to putative GREs in dexamethasone-transactivated promoters, SERPINE1, ANGPLT4, CCL20, and SAA1 as well as the NF-κB (p65) binding sites on GR-transrepressed promoters such as IL-1β, IL-6, and IL-8 Taken together, our data establish ACTN4 as a transcriptional co-regulator that modulates both dexamethasone-transactivated and -transrepressed genes in podocytes.

Long-term Outcomes of Childhood Onset Nephrotic Syndrome

There are limited studies on long-term outcomes of childhood onset nephrotic syndrome (NS). A majority of children with NS have steroid-sensitive nephrotic syndrome (SSNS). Steroid-resistant nephrotic syndrome (SRNS) is associated with a high risk of developing end-stage renal disease. Biomarkers and analysis of genetic mutations may provide new information for prognosis in SRNS. Frequently relapsing and steroid-dependent NS is associated with long-term complications, including dyslipidemia, cataracts, osteoporosis and fractures, obesity, impaired growth, and infertility. Long-term complications of SSNS are likely to be under-recognized. There remain many gaps in our knowledge of long-term outcomes of childhood NS, and further study is indicated.