In mice, a specific thyroid hormone receptor called TRα1 is not needed for thyroid hormone to affect energy production in fast-twitch muscle fibers, but it is required for thyroid hormone to increase...

Pro

Against

Mechanism

Synthesis from 1 study

How it works

In slow-twitch muscle, T3 needs TRα1 to turn on genes that make mitochondria burn energy as heat instead of making ATP, which increases respiration; in fast-twitch muscle, T3 can boost respiration without TRα1 using other unknown pathways, as shown by studies where removing TRα1 blocked the effect...

Most probable mechanism

In Simple Terms

In slow-twitch muscle, thyroid hormone T3 needs the TRα1 receptor to turn on genes like sarcolipin and UCP3, which make mitochondria waste energy as heat instead of making ATP, boosting respiration; in fast-twitch muscle, T3 can boost respiration without TRα1 because it uses other pathways that don’t rely on these genes, as shown by studies where removing TRα1 blocked the effect in slow-twitch muscle but not in fast-twitch muscle (10.1096/fj.202001258RR).

Causal chain

T3 binds to thyroid hormone receptor alpha 1 (TRα1) in slow-twitch skeletal muscle fibers, activating transcriptional programs that regulate thermogenic and metabolic genes (10.1096/fj.202001258RR).

Verified by multiple studies

which leads to

TRα1 activation increases expression of sarcolipin and UCP3 specifically in slow-twitch muscle, promoting uncoupling of mitochondrial respiration from ATP production and enhancing proton leak (10.1096/fj.202001258RR).

Verified by multiple studies

which leads to

Uncoupled mitochondrial respiration in slow-twitch muscle increases ATP turnover and oxygen consumption, elevating mitochondrial respiration rates in response to T3 (10.1096/fj.202001258RR).

Verified by multiple studies

which leads to

In fast-twitch muscle, T3 increases mitochondrial respiration through TRα1-independent mechanisms, such as direct modulation of mitochondrial enzymes or alternative nuclear receptors, since loss of TRα1 does not impair respiration in these fibers (10.1096/fj.202001258RR).

Supported by evidence

Evidence from Studies

Supporting (1)

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Thyroid hormone receptor α in skeletal muscle is essential for T3‐mediated increase in energy expenditure

Randomized Controlled Trial

Animal

2020 Nov

Contradicting (0)

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No contradicting evidence found

Gold Standard Evidence Needed

According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.

Source Study

Thyroid hormone receptor α in skeletal muscle is essential for T3‐mediated increase in energy expenditure

Score: 13

DOI: 10.1096/fj.202001258RR

Similar Assertions

In mice, the thyroid hormone T3 raises overall energy use by acting on a specific receptor, TRα1, in skeletal muscle. When this receptor is disabled in muscle tissue, the increase in energy use does not occur, even when T3 levels in the blood remain normal.

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In mice, the thyroid hormone T3 raises body temperature even when the thyroid hormone receptor TRα1 is not functional in skeletal muscle, indicating that the temperature increase does not depend on this specific receptor in muscle tissue.

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When thyroid hormone receptor alpha 1 is removed from the skeletal muscle of mice, the slow-twitch muscle fibers in the soleus muscle become more dominated by type I fibers and fewer type IIA fibers, but the mice's ability to run and their motivation to exercise remain unchanged.

74%

In mice, blocking a specific thyroid hormone receptor in muscle tissue leads to higher levels of sarcolipin mRNA in both slow- and fast-twitch muscle fibers, which may relate to how muscles generate heat.

74%