Thyroid Hormone and Non-Genomic TH Diseases Flashcards
What are the characteristics of nongenomic functions of TH?
It doesn’t act on nuclear receptors, it is a rapid effect, all forms of TH exert a nongenomic effect, small amplitude, involves signal transduction. Involves membrane receptors and/or modulation of intracellular pathways
What are the characteristics of genomic functions of TH?
It acts on nuclear receptors, slower, involves changing gene transcription, T3 causes genomic functions, large amplitude, no signal transduction
What are the rapid intracellular effects of TH?
ion flux, mitochondria activity (esp liver), glucose and aa uptake, actin polymerization (critical to remodelling, neural connections, cell movement, intracellular trafficking, muscle contraction, pseudopod formation)
What are some of the intracellular proteins that TH acts on?
Calmodulin, integrin, PIPs, cAMP, protein kinase –> these proteins cause rapid intracellular effects of TH
What are integrins?
Receptors that mediate attachment between a cell and other cells or the extracellular matrix
What is required to promote actin polymerization in rat brain cells for migration during development?
T4 and rT3, but not T3
What are the genomic and non-genomic effects of TH on cardiac myocytes?
T3 enters the cell by a specific transporter and acts in the nucleus via TR on the TRE. This causes transcription of genes involved in muscle contraction (myosin and actin). T3 also acts directly on voltage gated ion channels at the membrane (K+). These results act to increase heart rate.
How can the nongenomic effects of TH affect the TR in the nucleus?
Through phosphorylation cascades (CDK, MAPK, tyrosine kinase), when TR is phosphorylated it is activated, which causes co-repressor proteins to dissociate
What are the ways that there is cross talk between the non-genomic effects of TH at the membrane and the TR in the nucleus?
- T3 can bind to transporters on the membrane, which activates Na+/Ca+ exchangers to result in Ca signaling through calmodulin, as well as activate EGFR/PDGFR RTKs –> phosphorylate PKA –> enter the nucleus and cause TR phosphorylation, which leads to dissociation of co-repressors (like HDAC, NcoR, SMRT), this leads to binding of T3 which brings in coactivators: HAT, TRAP220, P160/SRCs –> gene transcription
- T4 can bind to integrin which can activate PKA or PKC –> Raf1 –> MEK –> MAPK –> enters nucleus and phosphorylates TR
- T3/T4 can also activate PLC, which increase the sensitivity of integrins by activating more PKC
What is the most common TH condition?
Hypothyroid
What effect does pregnancy have on the thyroid?
It puts high demand on the thyroid, can lead to hyperthyroidsim. There is a complex connection between thyroid hormones and estrogen, estrogen stimulates TSH and increases TBG (thyroid blood globulin) –> equilibrium may not shift
What is cretinism?
It is hypothyroidism in a developing child, leading to physical and mental disability
When can cretinism begin?
Can begin in utero if the mother has hypothyroidism
What are the symptoms of cretinism?
short stature, respiratory difficulty, jaundice, poor feeding, hoarse cry, lethargy, blue/purple skin, bone maturation delayed or permanently damaged, permanent lack of brain development
What is the cause of cretinism?
anti-TSH receptor antibodies from the mother (B cells producing antibodies that block binding of TSH to the receptor or T cells binding to TCRs that block binding –> mother has hashimotos), or could be due to severe iodine deficiency or defect in the baby’s thyroid axis