Henning Yoshiyuki, Vole Christiane, Begall Sabine, Bens Martin, Broecker-Preuss Martina, Sahm Arne, Szafranski Karol, Burda Hynek, Dammann Philip
Department of General Zoology, Faculty of Biology, University of Duisburg-Essen, Essen, Germany.
Genome Analysis, Leibniz Institute for Age Research - Fritz Lipmann Institute, Jena, Germany.
PLoS One. 2014 Nov 19;9(11):e113698. doi: 10.1371/journal.pone.0113698. eCollection 2014.
Ansell's mole-rats (Fukomys anselli) are subterranean, long-lived rodents, which live in eusocial families, where the maximum lifespan of breeders is twice as long as that of non-breeders. Their metabolic rate is significantly lower than expected based on allometry, and their retinae show a high density of S-cone opsins. Both features may indicate naturally low thyroid hormone levels. In the present study, we sequenced several major components of the thyroid hormone pathways and analyzed free and total thyroxine and triiodothyronine in serum samples of breeding and non-breeding F. anselli to examine whether a) their thyroid hormone system shows any peculiarities on the genetic level, b) these animals have lower hormone levels compared to euthyroid rodents (rats and guinea pigs), and c) reproductive status, lifespan and free hormone levels are correlated. Genetic analyses confirmed that Ansell's mole-rats have a conserved thyroid hormone system as known from other mammalian species. Interspecific comparisons revealed that free thyroxine levels of F. anselli were about ten times lower than of guinea pigs and rats, whereas the free triiodothyronine levels, the main biologically active form, did not differ significantly amongst species. The resulting fT4:fT3 ratio is unusual for a mammal and potentially represents a case of natural hypothyroxinemia. Comparisons with total thyroxine levels suggest that mole-rats seem to possess two distinct mechanisms that work hand in hand to downregulate fT4 levels reliably. We could not find any correlation between free hormone levels and reproductive status, gender or weight. Free thyroxine may slightly increase with age, based on sub-significant evidence. Hence, thyroid hormones do not seem to explain the different ageing rates of breeders and non-breeders. Further research is required to investigate the regulatory mechanisms responsible for the unusual proportion of free thyroxine and free triiodothyronine.
安塞尔鼹形鼠（福氏鼹形鼠）是穴居的长寿啮齿动物，生活在群居的家族中，繁殖者的最长寿命是非繁殖者的两倍。它们的代谢率显著低于基于异速生长法预期的水平，并且它们的视网膜显示出高密度的S-视锥蛋白视蛋白。这两个特征都可能表明其甲状腺激素水平天然较低。在本研究中，我们对甲状腺激素途径的几个主要成分进行了测序，并分析了繁殖和非繁殖的福氏鼹形鼠血清样本中的游离和总甲状腺素及三碘甲状腺原氨酸，以研究：a）它们的甲状腺激素系统在基因水平上是否有任何独特之处；b）与甲状腺功能正常的啮齿动物（大鼠和豚鼠）相比，这些动物的激素水平是否较低；c）繁殖状态、寿命和游离激素水平是否相关。基因分析证实，安塞尔鼹形鼠具有与其他哺乳动物物种已知的保守甲状腺激素系统。种间比较显示，福氏鼹形鼠的游离甲状腺素水平比豚鼠和大鼠低约十倍，而主要生物活性形式的游离三碘甲状腺原氨酸水平在物种间没有显著差异。由此产生的游离甲状腺素：游离三碘甲状腺原氨酸比值对哺乳动物来说是不寻常的，可能代表了一种自然低甲状腺素血症的情况。与总甲状腺素水平的比较表明，鼹形鼠似乎拥有两种截然不同的机制，这两种机制协同作用以可靠地下调游离甲状腺素水平。我们没有发现游离激素水平与繁殖状态、性别或体重之间存在任何相关性。基于不显著的证据，游离甲状腺素可能会随着年龄的增长而略有增加。因此，甲状腺激素似乎无法解释繁殖者和非繁殖者不同的衰老速度。需要进一步的研究来调查导致游离甲状腺素和游离三碘甲状腺原氨酸比例异常的调节机制。
