Age-dependent differences in methylation at specific cytosine–guanine (CpG) sites have been used in “epigenetic clock” formulas to predict age. Deviations of epigenetic age from chronological age are informative of health status and are associated with adverse health outcomes, including mortality. In most cases, epigenetic clocks are performed on methylation from DNA extracted from circulating blood cells. However, the effect of neoplastic cells in the circulation on estimation and interpretation of epigenetic clocks is not well understood. Here, we explored this using Fischer 344 (F344) rats, a strain that often develops large granular lymphocyte leukemia (LGLL). We found clear histological markers of LGLL pathology in the spleens and livers of 27 out of 61 rats aged 17–27 months. We assessed DNA methylation by reduced representation bisulfite sequencing with coverage of 3 million cytosine residues. Although LGLL broadly increased DNA methylation variability, it did not change epigenetic aging. Despite this, the inclusion of rats with LGLL in clock training sets significantly altered predictor selection probability at 83 of 121 commonly utilized CpG sites. Furthermore, models trained on rat samples that included individuals with LGLL had greater absolute age error than those trained exclusively rats free of LGLL (39% increase; p < .0001). We conclude that the epigenetic signals for aging and LGLL are distinct, such that LGLL assessment is not necessary for valid measures of epigenetic age in F344 rats. The precision and architecture of constructed epigenetic clock formulas, however, can be influenced by the presence of neoplastic hematopoietic cells in training set populations.

中文翻译：

---

大颗粒淋巴细胞白血病对 Fischer 344 大鼠血液 DNA 甲基化和表观遗传时钟建模的影响

特定胞嘧啶-鸟嘌呤 (CpG) 位点甲基化的年龄依赖性差异已被用于“表观遗传时钟”公式来预测年龄。表观遗传年龄与实足年龄的偏差是健康状况的重要信息，并与包括死亡率在内的不良健康结果相关。在大多数情况下，表观遗传时钟是根据从循环血细胞中提取的 DNA 的甲基化进行的。然而，循环中肿瘤细胞对表观遗传时钟的估计和解释的影响尚不清楚。在这里，我们使用 Fischer 344 (F344) 大鼠对此进行了探索，这种大鼠通常会发展为大颗粒淋巴细胞白血病 (LGLL)。我们在 17-27 个月大的 61 只大鼠中的 27 只的脾脏和肝脏中发现了明确的 LGLL 病理学组织学标志物。我们通过覆盖 300 万个胞嘧啶残基的减少代表性亚硫酸氢盐测序来评估 DNA 甲基化。尽管 LGLL 广泛增加了 DNA 甲基化变异性，但它并没有改变表观遗传衰老。尽管如此，在时钟训练集中包含 LGLL 大鼠显着改变了 121 个常用 CpG 位点中 83 个的预测因子选择概率。此外，在包含 LGLL 个体的大鼠样本上训练的模型比只训练没有 LGLL 的大鼠的模型具有更大的绝对年龄误差（增加 39%；p <.0001）。我们得出结论，衰老和 LGLL 的表观遗传信号是不同的，因此 LGLL 评估对于 F344 大鼠表观遗传年龄的有效测量不是必需的。然而，构建的表观遗传时钟公式的精度和结构，