Urinary Sediment mRNA As a Biomarker for IgAN

IgA nephropathy (IgAN) is the most common primary glomerulonephritis and a leading cause of chronic kidney disease (CKD). Renal biopsy is the leading method for diagnosing and predicting the progression of IgAN, but urinary biomarkers need to be identified to provide a less invasive and more reliable alternative. 

The quantification of mRNA expression in urinary sediment has emerged as a reliable biomarker for various diseases. However, not many studies have examined the clinical relevance of urinary mRNA levels in patients with IgAN. Dr. Jin Sug Kim and colleagues addressed this gap with a recent study, the results of which appeared in BMC Nephrology. 

Using the public Gene Expression Omnibus (GEO) repository and a literature review, the researchers identified the differential expression of mRNAs in renal tissue between patients with IgAN and healthy study participants and selected IgAN disease-specific mRNA candidates. They measured urinary expression levels of the mRNAs in patients with IgAN and compared them with those in control participants using quantitative, real-time polymerase chain reaction. In addition, they examined the relationship between urinary mRNA levels and the clinicopathologic parameters of patients with IgAN and analyzed the predictive value of each mRNA for CKD progression.  

Two hundred participants with biopsy-proven IgAN from two hospitals in South Korea were enrolled in the study between September 2010 and September 2019. The disease control group with non-IgAN nephropathy included six participants with lupus nephritis, 16 with minimal change disease (MCD), 17 with crescentic glomerulonephritis, and nine with membranous nephropathy (MN). An additional 76 individuals who did not have kidney disease were enrolled as healthy control participants.  

The mean age of the IgAN group was 42.4 years, 49.5% were male, and they had significantly higher serum albumin levels than participants in the control group. Participants with crescentic glomerulonephritis had significantly decreased renal function compared with that of participants with IgAN and other disease controls. Participants who had MN and MCD excreted significantly more urinary proteins than those with IgAN. The prevalence of diabetes and hypertension did not differ significantly between the groups.  

Baseline variables including age, sex, body mass index, and prevalence of hypertension and diabetes were recorded, and blood samples were collected to measure serum albumin, IgA, and creatinine. Urine samples were collected to measure urinary protein excretion and the presence of hematuria at the time of renal biopsy. 

Urinary protein excretion was calculated as the spot urine protein to creatinine ratio (PCR). The estimated glomerular filtration rate (eGFR) was used to measure renal function, calculated using the Chronic Kidney Disease Epidemiology Collaboration equation. The pathologic IgAN findings were described using the Oxford classification system.  

The participants with IgAN received angiotensin receptor blockers or angiotensin-converting enzyme inhibitors alone or in combination with immunosuppressants. Those patients visited the outpatient clinic every one to two months to have their renal function assessed. The clinical outcome was CKD progression (a greater than 50% reduction in the eGFR from the value determined at the time of renal biopsy or progression to end-stage renal disease). 

Researchers measured the levels of urinary candidate mRNAs in urine samples from participants in the IgAN, disease control, and healthy control groups. They found that urinary expression of CCL2, CD14, DNMT1, FKBP5, Nephrin, and IL-6 was significantly upregulated in the participants with IgAN compared with the healthy control participants.  

Levels of C3 (r=0.207; P=.005) and Podocin (r=0.162; P=.044) were significantly positively correlated with eGFR, whereas levels of FLOT1 (r=–0.206; P=0.004) were significantly negatively correlated with IgAN. Other urinary mRNAs did not demonstrate a significant correlation with renal function. 

C3, FLOT1, and TfR levels were significantly correlated with urinary protein excretion.  

Urine PCR demonstrated a negative correlation with urinary mRNA levels of C3 (r=–0.200; P=.007) and TfR (r=–0.184; P=.013), whereas the correlation of FLOT1 with urinary mRNA levels was positive (r=0.173; P=.017). 

In patients with mesangial hypercellularity, urinary mRNA levels of CCL2 (P=.028), DNMT1 (P=.049), and Podocin (P=.001) were significantly decreased. In patients with endocapillary hypercellularity, urinary mRNA levels of Podocin (P=.035) and PODXL (P=.003) were significantly elevated. In patients with tubular atrophy/interstitial fibrosis, urinary mRNA levels of IL-6 were significantly elevated (P=.040). No mRNAs demonstrated a significant correlation with segmental glomerulosclerosis or cellular or fibrocellular crescents. 

During follow-up, 26 (13.0%) participants with IgAN experienced disease progression (a greater than 50% reduction in eGFR or progression to end-stage renal disease). Multivariate analysis revealed that eGFR (hazard ratio [HR], 0.937; 95% CI, 0.904-0.973; P=.001), urine PCR (HR, 1.357; 95% CI, 1.019-1.808; P=.037), and urinary mRNA levels of FLOT1 (HR, 3.706; 95% CI, 1.373-10.005; P=.010) were independently associated with CKD progression among participants with IgAN. 

The authors acknowledge the limitations of their study. The mRNAs might reflect other conditions in addition to IgAN because the researchers selected candidates using GEO datasets based on comparisons of IgAN and healthy control participants. The researchers were unable to investigate the monitoring function of mRNAs due to the study design. Lastly, because of the small number of study participants, the authors could not pinpoint the clinical significance of mRNA in disease controls.  

In summary, the results imply that urinary mRNA expression signatures could provide useful biomarkers of IgAN and allow the differentiation of proteinuria resulting from active inflammation and chronic changes. The authors assert, “This distinction is crucial for clinical applications, as it enables more precise monitoring of disease activity and progression. By identifying the underlying cause of proteinuria, clinicians can more effectively tailor treatment strategies. The ability to noninvasively assess active inflammation versus chronic damage through urinary mRNA analysis provides a significant advantage in the management of IgAN.” 

Source: BMC Nephrology