申請者はこれまで、DNAメチル化やヒストン修飾などのエピゲノム変化の腎臓病病態への影響に注目して検討し報告してきた（JCI 2014, Kidney Int 2015）。また最近ではDNA損傷修復がエピゲノム変化形成の原因の一つであることを、糖尿病性腎症モデルを用いて明らかにした（Cell Rep 2019）。本研究では、最近報告されているエピゲノムワイド解析において、腎機能と血球細胞のDNAメチル化が関連していることに注目し、腎臓のDNA損傷・DNAメチル化変化と血球細胞のDNAメチル化の関連性について明らかにすることを目的とした。最近、老化研究領域で注目されているEpigenetic clock (EC)は機械学習で特定された重要領域のDNAメチル化レベルから計算されるDNAメチル化年齢であり、複数の疾患で促進が報告されているがCKDとの関連は不明であることから、まずECと腎臓のDNA損傷との関連を検討した。昨年度は比較的腎機能が保たれた当院予防医療センター受診者について検討を行ったが、今年度は腎臓内科外来通院中の腎機能低下症例も併せて検討を行った。人間ドックを受診した患者20名（年齢61.2±10.6、eGFR 62.8±10.1）、腎臓内科外来に通院中の患者8名（年齢61.3±10.1、eGFR 19.5±11.7）を対象に採血検体を用いてEPICアレイで85万ヶ所のCpGを解析し、既法のECであるHannum's clockを算出した。その結果、ECは暦年齢と有意に相関（p＜0.0001）し、CKD群ではEC-暦年齢が有意に増加し、生物学的な加齢との関連が示唆された（p=0.0028）。また、eGFRとEC-暦年齢は負の相関関係を示した（p=0.0008）。以上から、eGFRの低下と生物学的加齢との関連が示唆され、CKD患者におけるDNAメチル化年齢の進行を示した初の報告となった。今後、DNAメチル化プロファイルが変動する機序や原疾患別の更に詳細な検討が必要であると考える。
Prevalence of chronic kidney disease (CKD) is now increasing over the world due to the increase in the population of diabetes and hypertension patients, and in Japan, one in eight adults has CKD. There is not an effective therapy for CKD regression, therefore the establishment of novel strategies for conquering CKD is an urgent issue.
We have investigated the 'memory effect' in lifestyle-related diseases, which is a sustained effect of a transient treatment or insult, focusing the memory contained in the kidney. Recently we have demonstrated that epigenetic alterations in glomerular podocytes is involved in the memory effect in CKD (J Clin Invest 2014, Kidney Int 2015). In addition, the epigenetic alterations are associated with DNA damage repair, which is related to the pathogenesis of diabetic nephropathy (Cell Rep 2019). In this study, we aimed to clarify the relationship between kidney DNA damage and altered DNA methylation in blood cells, as the recently reported epigenome-wide analysis suggests the relationship between renal function and DNA methylation in blood cells. In addition, epigenetic clock (EC) has recently attracted attention in the field of aging research, which is a DNA methylation age calculated from DNA methylation levels in critical CpGs identified by machine learning. Its promotion has been reported in several diseases, but the association with CKD is unknown. Last year, we examined patients who had relatively preserved renal function at the Center for Preventive Medicine, Keio University Hospital, and this year we also examined patients with impaired renal function who were attending nephrology outpatient clinics. We analyzed 850,000 CpGs in 20 patients (age 61.2±10.6, eGFR 62.8±10.1) who underwent physical examination at the Center for Preventive Medicine and 8 patients (age 61.3±10.1, eGFR 19.5±11.7) who were attending nephrology outpatient clinics by EPIC array using blood samples, and calculated EC of Hannum's clock, as reported. The results showed that EC was significantly correlated with calendar age (p<0.0001), and EC-calendar age was significantly increased in the CKD group, suggesting an association with biological aging (p=0.0028). In addition, eGFR and EC-calendar age showed a negative correlation (p=0.0008). These results suggest an association between lower eGFR and biological aging, and this is the first report showing progression of DNA methylation age in CKD patients. We believe that further detailed investigation of the mechanisms of fluctuating DNA methylation profiles is needed in the future.