横隔膜は加齢による変化を認めない

高齢ラットの横隔膜は加齢による変化を認めないという研究を紹介します。

Andreas N. Kavazis, Keith C. DeRuisseau and Donna M. Gordon: The senescent rat diaphragm does not exhibit age-related changes in caspase activities, DNA fragmentation, or myonuclear domain. European Journal of Applied Physiology DOI: 10.1007/s00421-012-2380-2 Online First

抄録しか読んでいませんが、若いラットと高齢ラットで、横隔膜のタンパク質カルボニル（フリーラジカルによるタンパク質酸化の指標）、カスパーゼ活性化（細胞にアポトーシスを起こさせるシグナル伝達経路を構成）、DNA断片化、筋線維断面積、筋核ドメインを比較しました。

その結果、いずれも若いラットと高齢ラットで有意差を認めませんでした。これより横隔膜は加齢による変化や筋萎縮を認めないという結論です。あくまでラットでの話ですので、ヒトでそのまま当てはまるかどうかはわかりません。

加齢によるサルコペニアは、横隔膜では認めないのかもしれません。しかし、活動（人工呼吸器装着による廃用）、栄養（飢餓）、疾患（侵襲、悪液質、神経筋疾患）による二次性サルコペニアは、横隔膜にも認めると推測します。リハ栄養では老年医学以上に呼吸筋のサルコペニアが重要かもしれません。

Abstract
  The diaphragm muscle is essential for normal ventilation and it is chronically active throughout the lifespan. In most skeletal muscles, aging is associated with increased oxidative stress and myofiber atrophy. Since the diaphragm maintains a unique chronic contractile activity, we hypothesized that these alterations would not occur in senescent diaphragms compared to young diaphragms. In addition, we investigated whether senescence leads to altered diaphragmatic caspase activity and myonuclear domain. We harvested diaphragm muscles from 6 and 24–26 month old male Fisher 344 rats (n = 10 per group). Measurements of protein carbonyls, caspase 2, 3, 9, and 12 activities, DNA fragmentation, myofiber cross-sectional area, and myonuclear domain of diaphragm muscles were performed. No age-related changes (p > 0.05) in diaphragmatic protein oxidation or activities of caspase 2, 3, 9, and 12 were observed between groups. In addition, DNA fragmentation, as detected by the ligation-mediated polymerase chain reaction ladder assay, was not different (p > 0.05) between young and senescent diaphragms. Importantly, the cross-sectional area and myonuclear domain of diaphragm myofibers from senescent animals were also not different (p > 0.05) from young diaphragms. In conclusion, our data show that the senescent diaphragm does not atrophy or exhibit changes in select markers of the apoptotic pathway and this may be a result of the diaphragm’s unique continuous contractile activity.