The trajectory of the blood DNA methylome ageing rate is largely set before adulthood: evidence from two longitudinal studies.

The epigenetic clock, defined as the DNA methylome age (DNAmAge), is a candidate biomarker of ageing. In this study, we aimed to characterize the behaviour of this marker during the human lifespan in more detail using two follow-up cohorts (the Young Finns study, calendar age i.e. cAge range at baseline 15-24 years, 25-year-follow-up, N = 183; The Vitality 90+ study, cAge range at baseline 19-90 years, 4-year-follow-up, N = 48). We also aimed to assess the relationship between DNAmAge estimate and the blood cell distributions, as both of these measures are known to change as a function of age. The subjects' DNAmAges were determined using Horvath's calculator of epigenetic cAge. The estimate of the DNA methylome age acceleration (Δ-cAge-DNAmAge) demonstrated remarkable stability in both cohorts: the individual rank orders of the DNAmAges remained largely unchanged during the follow-ups. The blood cell distributions also demonstrated significant intra-individual correlation between the baseline and follow-up time points. Interestingly, the immunosenescence-associated features (CD8+CD28- and CD4+CD28- cell proportions and the CD4/CD8 cell ratio) were tightly associated with the estimate of the DNA methylome age. In summary, our data demonstrate that the general level of Δ-cAge-DNAmAge is fixed before adulthood and appears to be quite stationary thereafter, even in the oldest-old ages. Moreover, the blood DNAmAge estimate seems to be tightly associated with ageing-associated shifts in blood cell composition, especially with those that are the hallmarks of immunosenescence. Overall, these observations contribute to the understanding of the longitudinal aspects of the DNAmAge estimate.

Regulation of Jak2 tyrosine kinase by protein kinase C during macrophage differentiation of IL-3-dependent myeloid progenitor cells.

Differentiation of macrophages from myeloid progenitor cells depends on a discrete balance between cell growth, survival, and differentiation signals. Interleukin-3 (IL-3) supports the growth and survival of myeloid progenitor cells through the activation of Jak2 tyrosine kinase, and macrophage differentiation has been shown to be regulated by protein kinase C (PKC). During terminal differentiation of macrophages, the cells lose their mitogenic response to IL-3 and undergo growth arrest, but the underlying signaling mechanisms have remained elusive. Here we show that in IL-3-dependent 32D myeloid progenitor cells, the differentiation-inducing PKC isoforms PKC-alpha and PKC-delta specifically caused rapid inhibition of IL-3-induced tyrosine phosphorylation. The target for this inhibition was Jak2, and the activation of PKC by 12-O-tetradecanoyl-phorbol-13-acetate treatment also abrogated IL-3-induced tyrosine phosphorylation of Jak2 in Ba/F3 cells. The mechanism of this regulation was investigated in 32D and COS7 cells, and the inhibition of Jak2 required catalytic activity of PKC-delta and involved the phosphorylation of Jak2 on serine and threonine residues by the associated PKC-delta. Furthermore, PKC-delta inhibited the in vitro catalytic activity of Jak2, indicating that Jak2 was a direct target for PKC-delta. In 32D cells, the inhibition of Jak2 either by PKC-delta, tyrosine kinase inhibitor AG490, or IL-3 deprivation caused a similar growth arrest. Reversal of PKC-delta-mediated inhibition by the overexpression of Jak2 promoted apoptosis in differentiating 32D cells. These results demonstrate a PKC-mediated negative regulatory mechanism of cytokine signaling and Jak2, and they suggest that it serves to integrate growth-promoting and differentiation signals during macrophage differentiation. (Blood. 2000;95:1626-1632)