The expression of apoptotic genes in autoimmune thyroid diseases
S Waheed, LJ Hammond, PA Biro & R Mirakian
In thyroid autoimmune conditions such as Graves' disease, thyroid cells die by apoptosis (programmed cell death).
Dysregulation of pro- and anti-apoptotic genes may be critical to the induction of the destructive process via the activation of a sequence of caspases (proteases). Conventionally, apoptosis occurs via 2 main pathways: the Intrinsic pathway mediated by mitochondria and the Extrinsic pathway mediated by the activation of death receptors (Fas and TNFR). Both pathways converge downstream with the activation of effector caspases. The application of gene array technology allows both pathways to be studied simultaneously.
(i) To clarify whether classical or alternative pathways are responsible for apoptosis
(ii) To identify which pro- and anti-apoptotic genes are being expressed in thyroid autoimmune conditions
Total RNA was extracted from enriched thyrocyte preparations from 6 thyroids with Multinodular Goitre (control group) and 6 thyroids with Graves' disease. Local Ethical Committee approval was obtained. The RNA was transcribed into cDNA and hybridised to 96 apoptotic gene specific cDNA fragments printed onto a nylon membrane. The data were analysed using Scanalyze software.
TNFR2 was strongly expressed in both thyroid conditions indicating that the death signal appears to occur through this rather than Fas/FasL. There was increased expression of pro-apoptotic genes of the Bcl-2 Family (BAD, BAK) and caspase 13 and 14 in Graves compared to the control group. There was no differential expression in the 2 conditions of Bcl-2, Bcl-XL(anti-apoptotic genes) and Fas/FasL
Our results show that in Graves' disease there may be a non-conventional pathway of apoptotic activation. Tracing the pathways that cause cell death should enable the development of novel reagents for disease prevention. Also, as the thyroid is a readily accessible model of organ-specific autoimmunity our finding may provide an insight into other autoimmune diseases, such as Insulin Dependent Diabetes Mellitus.