cells Review Dissecting Aging and Senescence—Current Concepts and Open Lessons 1,2, , 1,2, 1 1,2 Christian Schmeer * y , Alexandra Kretz y, Diane Wengerodt , Milan Stojiljkovic and Otto W. Witte 1,2 1 Hans-Berger Department of Neurology, Jena University Hospital, 07747 Jena, Thuringia, Germany;
[email protected] (A.K.);
[email protected] (D.W.);
[email protected] (M.S.);
[email protected] (O.W.W.) 2 Jena Center for Healthy Ageing, Jena University Hospital, 07747 Jena, Thuringia, Germany * Correspondence:
[email protected] These authors have contributed equally. y Received: 2 October 2019; Accepted: 13 November 2019; Published: 15 November 2019 Abstract: In contrast to the programmed nature of development, it is still a matter of debate whether aging is an adaptive and regulated process, or merely a consequence arising from a stochastic accumulation of harmful events that culminate in a global state of reduced fitness, risk for disease acquisition, and death. Similarly unanswered are the questions of whether aging is reversible and can be turned into rejuvenation as well as how aging is distinguishable from and influenced by cellular senescence. With the discovery of beneficial aspects of cellular senescence and evidence of senescence being not limited to replicative cellular states, a redefinition of our comprehension of aging and senescence appears scientifically overdue. Here, we provide a factor-based comparison of current knowledge on aging and senescence, which we converge on four suggested concepts, thereby implementing the newly emerging cellular and molecular aspects of geroconversion and amitosenescence, and the signatures of a genetic state termed genosenium.