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Identifying new markers of disease flares in lupus nephritis (LN) that facilitate patient stratification and prognosis is important. Therefore, the aim of the present study was to analyze whether urinary SIRT1 expression was altered in LN and whether SIRT1 values in urine could be valuable biomarker of disease activity. In a cohort study, urinary pellets from 40 patients diagnosed with systemic lupus erythematosus (SLE) were analyzed. Clinical measures of lupus activity were assessed. The expression of SIRT1 was quantified by quantitative PCR (qRT-PCR) and immunoblot, then compared between patients with active lupus nephritis, in remission and healthy controls. Association with lupus activity and renal histological features was also analyzed. A significant increase in SIRT1 mRNA levels in patients with active LN was observed compared with those in remission (P=0.02) or healthy controls (P=0.009). In addition, SIRT-1 protein levels were also augmented in LN group than remission (P=0.029) and controls (P=0.001). A strong association was found between SIRT1 expression with anti-dsDNA in SLE and in patients with LN. In addition, histological features in LN biopsies were related with SIRT1, increasing its expression in proliferative forms. Finally, SIRT1 expression values showed a strong discriminatory power of renal injury in SLE. Our study demonstrated an altered urinary expression of SIRT1 and a strong association with disease activity in LN patients, being a valuable marker of renal injury. These results showed the role of the SIRT1 pathway in the SLE pathogenesis. [ABSTRACT FROM AUTHOR]