Thyroid Hormone Receptors in Human Skin during Aging

Abstract

Published data suggest that thyroid hormones play a role in the regulation of dermal fibroblasts during aging. This goal of this work was to study the levels of thyroid hormone receptors in human dermal fibroblasts, from embryonic development to extreme old age. Skin specimens from human fetuses that died antenatally from 20 to 40 weeks of pregnancy and humans who died from different causes from birth to age 85 years were used for the study. The total number of fibroblasts, the percentage of dermal fibroblasts positive for proliferating cell nuclear antigen (PCNA), and the expression of thyroid hormone receptors α and β in dermal fibroblasts were examined. PCNA and thyroid hormone receptors were viewed immunohistochemically. The total fibroblast number in the dermis was counted in sections stained with hematoxylin and eosin. The results showed that the maximal levels of thyroid hormone receptors α and β were observed from the 20th to 40th weeks of pregnancy. The levels of thyroid hormone receptors α and β were decreased from birth to age 40 years. From 41 to 85 years, the levels of thyroid hormone receptors were approximately the same. The total number and percentage of PCNA-positive fibroblasts in the dermis were decreased with progression of age. The most significant age-dependent reduction in the total and PCNA-positive number of dermal fibroblasts was observed from the antenatal period to the age of 40. Correlation analysis and one-way ANOVA showed that age-dependent decrease in the number of fibroblasts and the retardation of their proliferation in the human dermis is significantly associated with an age-related decrease in the level of thyroid hormone receptors α and β in dermal fibroblasts. The results suggest that thyroid hormone receptors are involved in an age-dependent decrease in the number and proliferation of fibroblasts in human dermis.