Glomerular Transcriptome Profiles in Focal Glomerulosclerosis: New Genes and Pathways for Steroid Resistance

Patients with focal segmental glomerulosclerosis (FSGS) characterized by steroid-resistant nephrotic syndrome (SRNS) are prone to progress to ESRD. Mechanism for the FSGS patients' response to steroid treatment is still unknown and currently, it is impossible to predict the steroid resistance before treatment of patients with FSGS.

To identify biomarkers and potential therapeutic targets of FSGS patients with SRNS, patients diagnosed as kidney biopsy-proven FSGS and nephrotic syndrome (NS) were prospectively enrolled. They were divided into 2 groups, steroid-sensitive NS and SRNS based on their treatment response. Cortical regions were selected from biopsied renal tissues, and glomeruli were isolated under an inverted microscope. RNA was prepared from the isolated glomeruli and further used for microarray analysis. Followed by multiple analyses, the top 6 highest and lowest, and a selected panel of differentially expressed genes obtained and their related pathways were validated via real-time PCR, western blot, and measurement of reactive oxygen species (ROS).

In SRNS group, we discovered that the most significant up-regulated pathway was primarily related to cellular amino acid and derivative metabolic process. Meanwhile, the most significant down-regulated pathway was primarily involved in anatomical structure morphogenesis. Moreover, we found NADPH oxidase 4 (NOX4), one of the key regulators of renal ROS, at a much higher level in SRNS both at transcriptomic and proteomic levels. We also found the levels of ROS, p-p38 MAPK and matrix metalloproteinase (MMP)-2, which were all regulated by NOX4, were also higher in glomeruli isolated from SRNS patients. At last, we detected stimulated by retinoic acid gene 6 homolog (STRA6), a cell surface receptor formerly known as a gene preventing podocytes from over-proliferative lesion induced by HIV infection and was up-regulated by retinoic acid, expressed at a much higher level in SRNS kidneys.

We found 2 potential mechanisms underline the SRNS, NOX4/ROS/P38 MAPK/MMP-2 pathway and STRA6. Our findings provided new insights into the steroid resistance.