Assessment of serum protein dynamics by native SILAC flooding (SILflood)

Turnover of blood serum proteins is a vital function in mammals, but technical challenges have thus far prevented comprehensive measurements of serum protein half-lives. Here, we injected native serum from heavy stable isotope labeled (SIL) mice into nonlabeled recipients to quantify turnover of more than 200 proteins using mass spectrometry with high reproducibility and accuracy. We found a median of 19.4 h and a total range of 6-70 h for calculated half-lives. Moreover, we observed similar half-lives for proteins with equal function. To demonstrate the value and effectiveness of SILflood, we investigated the impaired serum clearance in β2-microglobulin (B2M-/-) deficient mice. Notably, we found that serum albumin and IgG half-lives were clearly reduced in B2M deficient animals compared to control animals. Taken together, our results demonstrate that SILflood is a versatile tool to investigate serum half-lives under regular and pathological conditions in living animals.