Cdkn2a encodes different transcripts involved mostly in cell cycle regulation and cellular senescence [12882406], but it can also act as a tumor suppressor. Its expression level increase with age in rodents [15520862]. super-Ink4a/Arf mice carrying a transgenic copy of a large genomic segment containing an intact and complete copy of the Cdkn2a (a.k.a. Ink4a/Arf) gene are significantly protected from cancer and had no indication of accelerated aging. Cells derived from super-Ink4a/Arf mice have increased resistance to in vitro immortalization and oncogenic transformation [15520276]. Loss of Cdkn2a in mice results in tumour susceptibility [11544530]. Mice deficient in Cdkn2a have smaller age-related decline in self-renewal potential as this process is associated with increasing levels of Cdkn2a [16957738].

Increased levels of p16 are associated with aging (Krishnamurthy et al., 2006; Molofsky et al., 2006) and a bona fide marker of cellular senescence (Collado et al., 2007). p16INK4a accumulates in many tissues as a function of advancing age (Krishnamurthy et al., 2004; Nielsen et al., 1999; Zindy et al., 1997) and is an effector of senescence (Campisi, 2003; Park et al., 2004), p16INK4a is a potent inhibitor of proliferative kinase Cdk4 (Lowe and Sherr, 2003) which is essential for pancreatic ?-cell proliferation in adult mammals (Rane et al., 1999; Tsutsui et al., 1999). p16INK4a constrains islet proliferation and regeneration in an age-dependent manner. Expression of the p16INK4a transcript is enriched in purified islets compared with the exocrine pancreas and islet-specific expression of p16INK4a increases markedly with aging (Krishnamurthy et al., 2006). Aging in mammals is associated with reduced regenerative capacity in tissues that contain stem cells (Chien and Karsenty, 2005) which is probably partially caused by senescence of progenitors with age (Campisi, 2005; Lombard et al., 2005). Progenitor proliferation in subventricular zone and neurogenesis in the olfactory bulb as well as multipotent progenitor frequency and self-renewal potential, all decline with ageing the mouse forebrain. The decline in progenitor frequency and function correlate with increased expression of p16INK4a (Molofsky et al., 2006). Aging p16INK4a-deficient mice exhibit a significantly smaller decline in subventricular zone proliferation, olfactory bulb neurogenesis and the frequency and self-renewal potential of multipotent progenitors (Molofsky et al., 2006).

p16 expression in skin cells is significantly lower the the group that has a strong family history of longevity. As such a younger biological age associates with lower levels of p16INKfa positive cells [22612594].

p16 expression increases exponentially with age. Expression of p16INK4a with age does not predict cancer development. p16INK4a activation is a characteristic of all emerging cancers [http://denigma.de/url/3n].

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