Serum progranulin levels are associated with frailty in middle-aged individuals

Background and objective A recent study identified progranulin as a candidate biomarker for frailty, based on gene expression databases. In the present study, we investigated associations between serum progranulin levels and frailty in a population-based sample of late middle-age and older adults. Methods We utilized a cohort study that included 358 African Americans (baseline ages 49-65). Frailty was assessed by three established methods: the interview-based FRAIL scale, the Cardiovascular Health Study (CHS) frailty scale that includes performance-based measurements, and the Frailty Index (FI) that is based on cumulative deficits. Serum levels of the following proteins and metabolites were measured: progranulin, cystatin C, fructosamine, soluble cytokine receptors (interleukin-2 and -6, tumor necrosis factor alpha-1 and -2), and C-reactive protein. Sarcopenia was assessed using the SARC-F index. Vital status was determined by matching through the National Death Index (NDI). Results Serum progranulin levels were associated with frailty for all indices (FRAIL, CHS, and FI) but not with sarcopenia. Inflammatory markers indicated by soluble cytokine receptors (sIL-2R, sIL-6R, sTNFR1, sTNFR2) were positively associated serum progranulin. Increased serum progranulin levels at baseline predicted poorer outcomes including future frailty as measured by the FRAIL scale and 15-year all-cause mortality independent of age, gender, and frailty. Conclusions Our findings suggest that serum progranulin levels may be a candidate biomarker for physical frailty, independent of sarcopenia. Further studies are needed to validate this association and assess the utility of serum progranulin levels as a potential biomarker for prevalent frailty, for risk for developing incident frailty, and for mortality risk over and above the effect of baseline frailty.