Insolubilome profiling defines molecular features that influence protein insolubility with aging

Solubility regulates protein function, but how it is governed by aging remains elusive. Here, we utilized mass spectrometry to define the relative composition of the soluble and insoluble tissue/organ fractions during mouse aging. In the young, there is a wide (∼100-1,000×) range of insoluble/soluble protein ratios that differ tissue-specifically. With aging, some proteins become relatively more insoluble, while others are conversely regulated or unaffected. Age-related insoluble/soluble changes are not merely dictated by histological similarity, diverge in related tissues with distinct degeneration propensities, and correlate tissue-specifically with structural features. Proteins that become age-insoluble in multiple organs include aggregation-prone circulating factors and ectopically expressed proteins. For instance, although primarily expressed by the epidermis, hornerin insolubility increases with aging in skeletal muscle, and experimental hornerin upregulation causes muscle weakness. Thus, age-insoluble proteins are useful biomarkers but can also contribute to age-related functional decline, highlighting a multifaceted remodeling of the insolubilome with aging.