Top-Down Mass Spectrometry and Its Current Applications in Biomarker Discovery in Aging and Age-Related Diseases.

Aging is one of the most complex biological processes, which leads to a gradual decline in the function of organs, tissues and cells, and significant increases in the risks of many age-associated diseases, including cancer, neurodegenerative disorders, and cardiovascular diseases. Protein biomarkers have attracted increasing attention in research on aging and age-related diseases. Considering the fact that proteins are large heterogenous biomolecules due to coding polymorphisms, alternative RNA splicing and post-translational modifications (PTMs), including glycosylation, phosphorylation, and methylation, mass spectrometry (MS)-based top-down proteomics (TDP) is a powerful technology that allows for measuring proteins without proteolysis, thus characterizing intact forms of proteins, which provides information on primary sequences, including their modifications. This review provides an overview of TDP technologies, with a particular focus on the separation, ionization, and fragmentation of intact proteins and introduces the most recent applications of TDP to the discovery of proteoform-resolved biomarkers associated with aging and age-related diseases.