Publications in Nature Aging

Cerebrospinal fluid (CSF) proteins and their structures have been implicated in aging and neurodegenerative diseases. In the present study, we used limited proteolysis–mass spectrometry (LiP–MS) to screen for new aging-associated changes in the CSF proteome using a modified analysis. We found 38 protein groups that change in abundance with aging, predominantly immunoglobulins of the IgM subclass. We discovered six high-confidence candidates that underwent structural changes with aging, of which Kng1, Itih2, Lp-PLA2 and 14-3-3 proteins have binding partners or chemical forms known previously to change in the brains of patients with Alzheimer’s disease. Orthogonal validation by western blotting identified that the LiP–MS hit Cd5l forms a covalent complex with IgM in mouse and human CSF, the abundance of which increases with aging. In human CSF, SOMAmer probe signals for all six LiP–MS hits were associated with cognitive function and/or biomarkers of neurodegeneration, especially 14-3-3 proteins YWHAB and YWHAZ. Together, our findings show that LiP–MS can uncover age-related structural changes in CSF with relevance to neurodegeneration.

Neurofilament light chain (NfL) has emerged as a promising blood biomarker for the progression of various neurological diseases. NfL is a structural protein of nerve cells, and elevated NfL levels in blood are thought to mirror damage to the nervous system. We find that plasma NfL levels increase in humans with age (n = 122; 21–107 years of age) and correlate with changes in other plasma proteins linked to neural pathways. In centenarians (n = 135), plasma NfL levels are associated with mortality equally or better than previously described multi-item scales of cognitive or physical functioning, and this observation was replicated in an independent cohort of nonagenarians (n = 180). Plasma NfL levels also increase in aging mice (n = 114; 2–30 months of age), and dietary restriction, a paradigm that extends lifespan in mice, attenuates the age-related increase in plasma NfL levels. These observations suggest a contribution of nervous system functional deterioration to late-life mortality.

Organismal aging is often characterized as a steady, monotonic decline of organ and tissue function. However, recent studies indicate spatial and temporal variations of aging rates across the lifespan. We consider these variations from the perspective of underlying cellular changes. Cells in certain tissues may age earlier and produce signals that accelerate the aging of other cells, locally or distantly, acting as drivers for organismal aging and leading to a lack of synchronous aging between tissues. As cells adopt new homeostatic states, cellular aging can be viewed, at least in part, as a quantal process we refer to as digital aging. Analog declines of tissue function with age may be the sum of underlying digital events. Cellular aging, digital or otherwise, is not uniform across time or space within organisms or between organisms of the same species. Advanced systems-level and single-cell methodologies will refine our understanding of cell and tissue aging, and how these processes integrate to produce the complexities of individual, organismal aging.