Thyroid Hormone–Mitochondrial Axis in ME/CFS
1 Sun et al. 2023 — Selenoprotein P Autoantibodies and Acquired Thyroid Hormone Resistance
Full Citation:: Sun Q, Oltra E, Engström K, Scheibenbogen C, Seissler N, Wang X, Schomburg L. Autoantibodies to selenoprotein P in chronic fatigue syndrome suggest selenium transport impairment and acquired resistance to thyroid hormone. Redox Biology. 2023;65:102796. DOI:: 10.1016/j.redox.2023.102796 PMID:: 37392583 PMCID:: PMC10338150 Published:: July 2023 Study Design:: Case-control study (two independent ME/CFS cohorts) Sample Size:: \(n = 167\) ME/CFS patients across two cohorts, \(n = 545\) healthy controls Key Findings::
- Autoantibodies to selenoprotein P (SELENOP-aAb) present in 9.6--15.6% of ME/CFS patients vs 0.9--2.0% of controls (~10-fold enrichment)
- SELENOP-aAb--positive patients showed lowest deiodinase activity (SPINA-GD: 13.1 vs 15.8, $p < 0.001$)
- Reduced FT3/FT4 ratio (27.7 vs 34.0, $p < 0.001$) and TT3/TT4 ratio (1.84 vs 2.19, $p = 0.005$)
- Dramatically lower urinary iodine (43.2 vs 89.0 $\mu$g/L, $p < 0.001$)
- Loss of normal correlation between serum selenium and GPx3 activity in SELENOP-aAb--positive patientsConclusion:: A subset of ME/CFS patients has autoantibodies that impair selenium transport, producing acquired thyroid hormone resistance through reduced tissue deiodinase activity. Limitations:: In-house ELISA; no commercial standardized assay. Tissue selenium not directly measured. Two cohorts from same research group. Relevance:: Provides the strongest mechanistic link between autoimmunity and the Low T3 Syndrome in ME/CFS. Explains why standard thyroid tests (TSH, FT4) can appear normal while tissues are functionally hypothyroid. Directly supports Selenoprotein P Autoantibodies in a Subset of ME/CFS Patients and the tissue T3 amplification hypothesis Low Tissue T3 as Amplifier of Mitochondrial Dysfunction in a Subset of ME/CFS Patients. Certainty Assessment::
- *Quality:* High (rigorous two-cohort design, multiple biomarker endpoints)
- *Replication:* Not yet replicated independently
- *Certainty:* 0.552 Singh & Yen 2022 — Bioenergetic Aspects of Mitochondrial Actions of Thyroid Hormones
Full Citation:: Singh BK, Yen PM. Bioenergetic Aspects of Mitochondrial Actions of Thyroid Hormones. Cells. 2022;11(6):997. DOI:: 10.3390/cells11060997 PMCID:: PMC8947633 Published:: March 2022 Study Design:: Comprehensive review Key Findings::
- T3 regulates all five ETC complexes plus ATP synthase through nuclear and direct mitochondrial pathways
- T3 promotes respiratory supercomplex assembly; hypothyroidism reduces supercomplex formation
- Biphasic ROS response: physiological T3 limits ROS via supercomplexes; excess or deficient T3 increases ROS
- T3 induces cardiolipin synthesis, essential for supercomplex stability
- T3 coordinates mitochondrial quality control: fission → mitophagy → biogenesis cycleConclusion:: T3 is a master regulator of mitochondrial bioenergetics at every level: biogenesis, function, quality control, and membrane composition. Relevance:: Provides the mechanistic foundation for the thyroid-mitochondria connection in ME/CFS. The supercomplex assembly function of T3 directly converges with the WASF3 supercomplex disruption mechanism (ER Stress–WASF3–Mitochondrial Dysfunction Pathway: Druggable Mechanism). Certainty Assessment::
- *Quality:* High (comprehensive review of well-established molecular biology)
- *Replication:* Core mechanisms extensively replicated across model systems
- *Certainty:* 0.85 (basic mechanisms); 0.45 (ME/CFS application)3 Liao et al. 2024 — Thyroid Hormone in Mitochondrial Regulation at the Interface of Health and Disease
Full Citation:: Liao C-H, et al. The key roles of thyroid hormone in mitochondrial regulation, at interface of human health and disease. Molecular and Cellular Endocrinology. 2024. PMCID:: PMC11522957 Published:: 2024 Study Design:: Comprehensive review Key Findings::
- Cardiolipin content directly tracks thyroid status; hypothyroidism depletes cardiolipin
- ~4 shared cardiolipins per Complex III/IV interface in supercomplexes
- T3 regulates phospholipid remodeling and membrane unsaturation
- Clinical disease states with mitochondrial dysfunction show consistent thyroid hormone abnormalitiesConclusion:: Thyroid hormone-mitochondrial interactions are clinically significant in multiple disease states and represent therapeutic targets. Relevance:: Provides the cardiolipin-supercomplex stability mechanism linking T3 deficiency to respiratory chain dysfunction in Section Endogenous Ouabain Depletion: A Missing Regulatory Signal for Na+/K+-ATPase?. Certainty Assessment::
- *Quality:* High (integrative review)
- *Replication:* Cardiolipin-thyroid relationship well established
- *Certainty:* 0.804 Wrutniak-Cabello et al. 2018 — Thyroid Hormone Action: The p43 Mitochondrial Pathway
Full Citation:: Wrutniak-Cabello C, Casas F, Cabello G. Thyroid Hormone Action: The p43 Mitochondrial Pathway. Methods in Molecular Biology. 2018;1801:163–181. DOI:: 10.1007/978-1-4939-7902-8_14 PMID:: 29892824 Published:: 2018 Study Design:: Methodological review with experimental data Key Findings::
- p43 (~43 kDa) is a truncated TR$\alpha$ 1 product imported into the mitochondrial matrix
- p43 binds T3 and functions as a T3-dependent transcription factor of mitochondrial DNA
- p43 promotes transcription of all 13 mtDNA-encoded OXPHOS subunits
- p28 (~28 kDa) localises to the inner mitochondrial membrane; function unknownConclusion:: Mitochondria have their own thyroid hormone receptor system that directly regulates mtDNA gene expression, independent of nuclear thyroid hormone signaling. Relevance:: Explains how T3 deficiency can impair mitochondrial function through a direct pathway that bypasses nuclear gene regulation entirely—tissue T3 deficit reduces both nuclear and mitochondrial OXPHOS gene expression simultaneously. Certainty Assessment::
- *Quality:* High (original researchers who discovered p43)
- *Replication:* p43 protein confirmed; functional significance debated
- *Certainty:* 0.705 Singh et al. 2017 — Thyroid Hormone Receptor and ERRα Coordinate Mitochondrial Quality Control
Full Citation:: Singh BK, Sinha RA, Tripathi M, et al. Thyroid hormone receptor and ERR\(\alpha\) coordinately regulate mitochondrial fission, mitophagy, biogenesis, and function. Science Signaling. 2017;10(486):eaam5855. DOI:: 10.1126/scisignal.aam5855 Published:: July 2017 Study Design:: Experimental (cell culture, mouse models) Key Findings::
- T3 induces DRP1-mediated mitochondrial fission through ESRRA-dependent ULK1 expression
- T3 simultaneously induces mitophagy (autophagy of damaged mitochondria) via the same pathway
- T3 promotes biogenesis of replacement mitochondria via PGC-1$\alpha$
- The coordinated fission-mitophagy-biogenesis cycle ensures mitochondrial quality controlConclusion:: T3 is essential for the complete mitochondrial turnover cycle; without T3, damaged mitochondria accumulate rather than being cleared and replaced. Relevance:: Directly relevant to ME/CFS: impaired mitophagy is documented (Section Cross-Cutting Mechanisms), and T3 deficiency provides a mechanistic explanation for why damaged mitochondria persist. Supports the amplification hypothesis Low Tissue T3 as Amplifier of Mitochondrial Dysfunction in a Subset of ME/CFS Patients. Certainty Assessment::
- *Quality:* High (*Science Signaling*, rigorous experimental design)
- *Replication:* Core pathway confirmed in multiple tissues
- *Certainty:* 0.806 Lombardi et al. 2015 — T2 and Skeletal Muscle Mitochondrial Regulation
Full Citation:: Lombardi A, de Lange P, Silvestri E, et al. Regulation of skeletal muscle mitochondrial activity by thyroid hormones: focus on the “old” triiodothyronine and the “emerging” 3,5-diiodothyronine. Frontiers in Physiology. 2015;6:237. DOI:: 10.3389/fphys.2015.00237 Published:: August 2015 Study Design:: Comprehensive review Key Findings::
- T2 binds Complex IV subunit Va, abolishing allosteric ATP inhibition
- T2 stimulates fatty acid oxidation (+80--104% with palmitoyl substrates) via SIRT1/AMPK
- T2 reduces H~2~O~2~ production while increasing respiration rate
- T2 effects are rapid (minutes), non-genomic, and independent of protein synthesisConclusion:: T2 is a biologically active thyroid metabolite with distinct mitochondrial effects complementary to T3. Relevance:: Opens the question of whether T2 deficiency contributes to exercise intolerance in ME/CFS (Are T2 Levels Altered in ME/CFS?). The rapid non-genomic mechanism suggests T2 may be critical for acute metabolic demand responses. Certainty Assessment::
- *Quality:* High (comprehensive review by leading T2 researchers)
- *Replication:* T2-Complex IV interaction well established; clinical significance debated
- *Certainty:* 0.757 Saito et al. 2025 — Mitochondrial Dysfunction in ME/CFS (Review)
Full Citation:: Saito A, Bi H, Hanai T, Suzuki K. Mitochondrial Dysfunction in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Physiology. 2025. DOI:: 10.1152/physiol.00057.2024 PMID:: 39960432 Published:: 2025 Study Design:: Systematic review Key Findings::
- Comprehensive synthesis of mitochondrial dysfunction evidence across OXPHOS, substrate oxidation, and morphology in ME/CFS
- Identifies thyroid hormone signaling as an under-investigated regulatory axis
- Highlights the gap between documented mitochondrial abnormalities and their upstream driversConclusion:: Mitochondrial dysfunction is a consistent feature of ME/CFS, but upstream regulatory mechanisms (including thyroid hormone signaling) remain insufficiently characterized. Relevance:: Current authoritative review confirming the mitochondrial dysfunction evidence base that the thyroid-mitochondrial hypothesis seeks to explain. Certainty Assessment::
- *Quality:* High (American Physiological Society journal)
- *Replication:* Review synthesises multiple independent studies
- *Certainty:* 0.758 Lowe et al. 1997 — T3 for Euthyroid Fibromyalgia
Full Citation:: Lowe JC, Garrison RL, Reichman AJ, Yellin J. Effectiveness and Safety of T3 Therapy for Euthyroid Fibromyalgia: A Double-Blind Placebo-Controlled Response-Driven Crossover Study. Clinical Bulletin of Myofascial Therapy. 1997;2(2–3). DOI:: 10.1300/J425v02n02_04 Published:: 1997 Study Design:: Double-blind placebo-controlled crossover RCT Key Findings::
- Supraphysiologic T3 doses were "safe and significantly effective" in euthyroid fibromyalgia
- Positive clinical response with acceptable adverse effect profile
- Response-driven design (dose titration to clinical response)Conclusion:: T3 supplementation can benefit euthyroid patients with fibromyalgia symptoms. Limitations:: Fibromyalgia is distinct from ME/CFS; direct extrapolation is unjustified. Supraphysiologic dosing carries cardiac and bone risks. Small sample size. Single study, not replicated. The lead author’s broader claims about “T3 resistance” were rejected by the American Thyroid Association. Relevance:: The only controlled trial of T3 in a fatiguing condition with ME/CFS symptom overlap. Provides proof-of-concept that euthyroid patients can respond to T3, but does not constitute evidence for T3 use in ME/CFS. Certainty Assessment::
- *Quality:* Moderate (controlled trial, but small and in a different condition)
- *Replication:* Not replicated
- *Certainty:* 0.35 (for ME/CFS applicability)9 Frontiers 2025 — Elevated mtDNA Copy Number in Impaired Peripheral Thyroid Sensitivity
Full Citation:: Elevated mitochondrial DNA copy number in euthyroid individuals with impaired peripheral sensitivity to thyroid hormones. Frontiers in Endocrinology. 2025. DOI:: 10.3389/fendo.2025.1635820 Published:: 2025 Study Design:: Cross-sectional analysis Key Findings::
- Euthyroid individuals with impaired peripheral sensitivity to thyroid hormones show elevated mtDNA copy number
- Interpreted as compensatory response to reduced T3 signaling at tissue level
- Supports the concept that tissue-level thyroid resistance produces measurable mitochondrial adaptations even when serum thyroid tests are normalConclusion:: Peripheral thyroid hormone resistance produces compensatory mitochondrial adaptations detectable by mtDNA copy number. Relevance:: Provides a measurable biomarker (mtDNA copy number) that could identify ME/CFS patients with tissue-level thyroid hormone resistance, even when standard thyroid tests are normal. Certainty Assessment::
- *Quality:* Moderate (single cross-sectional study)
- *Replication:* Not yet replicated
- *Certainty:* 0.50