Functional correlates of TSH, fT3 and fT4 in Alzheimer disease: a F-18 FDG PET/CT study

The disturbance of thyroid-associated hormone and its receptors in brain and blood circulation existed in the early stage of mouse model of Alzheimer's disease

BACKGROUND

Studies showed that thyroid function plays an important role in the pathology of Alzheimer's disease (AD). However, changes in brain thyroid hormone and related receptors in the early stage of AD were rarely reported. The aim of this study was to explore the relationship between the early stage of AD and local thyroid hormone and its receptors in the brain.

METHODS

The animal model was established by stereotactic injection of okadaic acid (OA) into hippocampal region for the experiment, and 0.9% NS for the control. Blood sample from each mouse was collected and then the mice were sacrificed and the brain tissue was collected for detecting free triiodothyronine (FT3), free thyroid hormone (FT4), and thyroid-stimulating hormone (TSH), thyrotropin-releasing hormone (TRH) and phosphorylated tau, amyloid-β (Aβ) and thyroid hormone receptors (THRs) in the hippocampus of the mice were detected as well.

RESULTS

Enzyme-linked immunosorbent assay showed that compared with the control, FT3, FT4, TSH and TRH in brain were significantly increased in the experimental group; in the serum, FT4, TSH and TRH were increased, while FT3 had no change; western blot analysis indicated that the expression of THR α and β in the hippocampus of the experimental group was significantly higher than that of the control.

CONCLUSION

Based on the results of this study, a mouse AD model can be established successfully by injecting a small dose of OA into the hippocampus. We speculate that early AD brain and circulating thyroid dysfunction may be an early local and systemic stress repair response.

Thyroid hormone levels in Alzheimer disease: a systematic review and meta-analysis

BACKGROUND AND OBJECTIVE

Thyroid hormone (TH) disturbances are perceived to contribute to cognitive impairment and dementia. However, there is no consensus on the association between TH levels and Alzheimer Disease (AD). In this study, we aimed to compare serum and cerebrospinal fluid (CSF) TH levels in AD patients to controls by performing a meta-analysis.

METHODS

We systematically searched online databases for papers comparing CSF or serum TH levels in AD patients to controls, and performed a meta-analysis on the extracted data.

RESULTS

Out of 1604 records identified, 32 studies were included. No significant difference in serum TSH (standardized mean difference (SMD): -0.03; 95% confidence interval (CI): -0.22-0.16), total T4 (SMD: 0.10; 95% CI: -0.29-0.49), and free T4 (SMD: 0.25; 95% CI: -0.16-0.69) levels were observed. However, there was significantly lower serum total T3 (SMD: -0.56; 95%CI: -0.97 to -0.15) and free T3 (SMD: -0.47; 95%CI: -0.89 to -0.05) levels in AD group compared to controls. Subgroup analyses on studies including only euthyroid patients did not show any significant difference in either of the thyroid hormone levels. Also, no significant difference in CSF total T4 and total T3/total T4 ratios but significantly lower CSF total T3 (SMD: -2.45; 95% CI: -4.89 to -0.02) in AD group were detected.

CONCLUSION

Serum total and free T3 and CSF total T3 levels are significantly lower in AD patients compared to controls. The temporality of changes in thyroid hormone levels and AD development should be illustrated by further longitudinal studies.

Thyroid Hormones and Health-Related Quality of Life in Normal Pressure Hydrocephalus Patients before and after the Ventriculoperitoneal Shunt Surgery: A Longitudinal Study

Objective: The aim of this study was to explore the serum levels of thyroid-stimulating hormone (TSH), free thyroxine (FT4), and free triiodothyronine (FT3), and to correlate the hormone levels among iNPH patients with their self-reported quality of life before and three months after the surgery. Methods: Twenty-five patients (52% women), mean age 63.5 (SD 9.5) years, were operated on by inserting a VP shunt. Patients with FT3 level ≤3.34 pmol/L were diagnosed as having low T3 syndrome. Results: The changes in thyroid hormones resulted in a U-shaped curve throughout the follow-up period. The significant changes occurred the next day after the surgery, including a decrease in TSH, FT3, and an increase in FT4. Additionally, the decrease occurred in mean FT3 for six patients with preoperative low T3 syndrome. Three months after the surgery, thyroid hormones were restored to their baseline and/or normal values. All six patients with preoperative low T3 syndrome had significant improvement in all SF-36 subscales (except for the role emotional and physical). Patients with preoperative normal high FT3 and low FT4 had increased FT3/FT4 ratio which was associated with deterioration in all SF-36 subscales 3 months after the surgery. Conclusion: Routine assessment of the FT3/FT4 ratio might be a simple and effective tool for the risk stratification of iNPH patients before VP shunt surgery.

Higher thyroid function is associated with accelerated hippocampal volume loss in Alzheimer's disease

BACKGROUND

In epidemiological studies, higher thyroid hormone (TH) levels have been associated with lower brain volume and increased risk of Alzheimer's disease (AD) in elderly individuals. However, the relationships between serum THs and hippocampal atrophy rates have previously not been investigated.

METHODS

A prospective study of patients with AD (n = 55), stable mild cognitive impairment (sMCI; n = 84) and healthy controls (n = 29) recruited at a single memory clinic. We investigated whether serum THs were associated with magnetic resonance imaging (MRI)-estimated hippocampal volumes at baseline and with longitudinal alterations, defined as annualized percent changes.

RESULTS

Serum levels of free triiodothyronine (FT3) and FT3/free thyroxine (FT4) ratio were reduced in AD and sMCI patients compared with the controls (p < 0.05). Hierarchical linear regression analyses showed that higher serum FT3/FT4 ratio was associated with greater baseline hippocampal volume in all study groups. Only in AD patients, higher serum FT4 was associated with lower baseline volume of the left hippocampus. Finally, exclusively in the AD group, higher serum levels of FT3 and FT3/FT4 ratio, and lower serum TSH levels, were associated with greater annual hippocampal volume loss.

CONCLUSIONS

In all study groups, FT3/FT4 ratio was related to baseline hippocampal volume. However, only in AD patients, higher levels of THs were associated with greater annual loss of hippocampal volume, suggesting that excessive TH levels exert a deleterious effect on the hippocampus in the presence of existing AD neuropathology.

Association of serum thyroid hormone levels with positron emission tomography imaging in non-demented older adults

BACKGROUND

Although increasing evidence indicates that even variations in normal range thyroid function are associated with Alzheimer's disease (AD), the association between serum thyroid hormone levels within the reference range and AD biomarkers remains unclear. This study examined whether variations in thyroid hormones within the reference range are associated with brain amyloid burden and cortical glucose metabolism in older adults without dementia.

METHODS

One hundred and two non-demented older adults underwent ¹¹ C-Pittsburgh Compound B positron emission tomography (PiB-PET), ¹⁸ F-fluorodeoxyglucose (FDG)-PET, and measurement of serum thyroid-stimulating hormone (TSH), free triiodothyronine (T3), and free thyroxine (T4) levels. The discrimination between PiB-negative and PiB-positive subgroup was made on the basis of a subject's cortical uptake value ratio greater than 1.4. The association of serum thyroid hormone levels with global PiB or FDG uptake, and PiB or FDG uptake in each region of interest, including frontal and temporoparietal lobes and posterior cingulate gyrus, was analysed using a multiple regression model with adjustment for covariates, including age, gender, years of education, apolipoprotein E4 status or PiB uptake value.

RESULTS

In the PiB-positive subgroup, the serum TSH levels positively associated with the global FDG uptake (β = 0.471, P = 0.003) and FDG uptake in the frontal and temporoparietal lobes (β = 0.466, P = 0.003, β = 0.394, P = 0.012, respectively); the serum-free T3 levels negatively associated with the FDG uptake in the temporoparietal lobe and posterior cingulate region (β = -0.351, P = 0.033, β = -0.544, P = 0.002, respectively). The PiB-negative subgroup showed no significant associations. The serum thyroid hormone levels did not correlate with the global PiB uptake and PiB uptake in each region.

CONCLUSIONS

The variations in the thyroid hormones within the reference ranges are associated with glucose metabolism, particularly in the specific regions affected by the neuropathologic changes of AD, in non-demented older adults with brain amyloid burden.

No effect of thyroid hormones on 5-year mortality in patients with subjective cognitive decline, mild cognitive disorder, and Alzheimer's disease

The present study aimed to investigate differences in circulating thyroid hormone levels, gender, education, depressive symptoms, and cognitive performance among patients with cognitive impairment, and also to examine their associations, as well as that of cognitive decline, with 5-year mortality. Between 1998 and 2017, a hospital-based, single-centre (Neurology Department of the General Hospital in Vienna, Austria), retrospective follow-up study enrolled 2102 patients with mild to severe cognitive impairment (grouped into subjective cognitive decline, mild cognitive impairment, and Alzheimer's disease). Cox proportional hazards models were used to calculate hazard ratios (HRs), with 95% confidence intervals (CIs), as well as to calculate stepwise adjustments for demographic variables (age, gender, and education), depressive symptoms (Geriatric Depression Scale, GDS-15), and neuropsychological abilities (four domains of a neuropsychological test battery of Vienna, NTVB). In univariate analyses, total triiodothyronine (TT3) levels differed significantly between Alzheimer's disease and mild cognitive impairment patients (p_diff  = .001). No other differences in cognitive impairment subgroups with any of the measured thyroid hormones were observed. Furthermore, in multivariate models, circulating TT3 was not associated with mortality (multivariable-adjusted HR per unit increase in TT3 = 0.56; 95% CI = 0.29-1.07). In multivariate models, we observed significantly lower 5-year mortality among women (HR = 0.56; 95% CI = 0.43-0.73) and those who scored higher on any of the four domains of the NBTV (e.g., attention and perceptual speed, HR = 0.63; 95% CI = 0.54-0.72); we also observed significantly higher 5-year mortality among patients with depressive symptoms (HR per one point score increase in GDS-15 = 1.06; 95% CI = 1.02-1.10), regardless of cognitive impairment subgroup. Among patients with various degrees of cognitive impairment, we found no associations of thyroid hormone levels with 5-year mortality. Gender, neuropsychological abilities, and depressive symptoms were each significant predictors of 5-year mortality. These results suggest that a neurocognitive test performance could serve as an important predictor of 5-year mortality among patients with cognitive impairment, although further studies with a more complete adjustment for comorbidities are needed to confirm these findings.

Connectivity and variability of related cognitive subregions lead to different stages of progression toward Alzheimer's disease

Single modality MRI data is not enough to depict and discern the cause of the underlying brain pathology of Alzheimer's disease (AD). Most existing studies do not perform well with multi-group classification. To reveal the structural, functional connectivity and functional topological relationships among different stages of mild cognitive impairment (MCI) and AD, a novel method was proposed in this paper for the analysis of regional importance with an improved deep learning model. Obvious drift of related cognitive regions can be observed in the prefrontal lobe and surrounding the cingulate area in the right hemisphere when comparing AD and healthy controls (HC) based on absolute weights in the classification mode. Alterations of these regions being responsible for cognitive impairment have been previously reported. Different parcellation atlases of the human cerebral cortex were compared, and the fine-grained multimodal parcellation HCPMMP performed the best with 180 cortical areas per hemisphere. In multi-group classification, the highest accuracy achieved was 96.86% with the utilization of structural and functional topological modalities as input to the training model. Weights in the trained model with perfect discriminating ability quantify the importance of each cortical region. This is the first time such a phenomenon is discovered and weights in cortical areas are precisely described in AD and its prodromal stages to the best of our knowledge. Our findings can establish other study models to differentiate the patterns in various diseases with cognitive impairments and help to identify the underlying pathology.

Comparison of Serum Triiodothyronine with Biomarkers for Alzheimer's Disease Continuum in Euthyroid Subjects

BACKGROUND

Accumulating studies have implicated thyroid dysfunction in the pathogenesis of Alzheimer's disease (AD).

OBJECTIVE

This study aimed to explore the association between thyroid hormone (TH) levels and cerebrospinal fluid (CSF) biomarkers for AD continuum among euthyroid subjects.

METHODS

In all, 93 clinically euthyroid subjects with a cognitive decline were included in this prospective cross-sectional study and were divided into groups with abnormal AD biomarkers (belonging to the "Alzheimer's continuum"; A+ patients) and those with "normal AD biomarkers" or "non-AD pathological changes" (A-patients), according to the ATN research framework classification for AD. A partial correlation analysis of serum thyroid-stimulating hormone (TSH) or TH levels with CSF biomarkers was conducted. The predictor for A+ patients was analyzed via binary logistic regressions. Finally, the diagnostic significance of individual biochemical predictors for A+ patients was estimated via receiver operating characteristic curve analysis.

RESULTS

Serum total triiodothyronine (TT3) and free triiodothyronine (FT3) levels were found to affect the levels of CSF amyloid-β (Aβ)42 and the ratios of Aβ 42/40. Further, FT3 was found to be a significant predictor for A+ via binary logistic regression modeling. Moreover, FT3 showed a high diagnostic value for A+ in euthyroid subjects.

CONCLUSION

Even in a clinical euthyroid state, low serum FT3 and TT3 levels appear to be differentially associated with AD-specific CSF changes. These data indicate that serum FT3 is a strong candidate for differential diagnosis between AD continuum and non-AD dementia, which benefits the early diagnosis and effective management of preclinical and clinical AD patients.

Association between thyroid function and Alzheimer's disease: A systematic review

Alterations in metabolic parameters have been associated with an increased risk of dementia, among which thyroid function has gained great importance in Alzheimer's disease (AD) pathology in recent years. However, it remains unclear whether thyroid dysfunctions could influence and contribute to the beginning and/or progression of AD or if it results from AD. This systematic review was conducted to examine the association between thyroid hormone (TH) levels and AD. Medline, ISI Web of Science, EMBASE, Cochrane library, Scopus, Scielo, and LILACS were searched, from January 2010 to March 2020. A total of 17 articles were selected. The studies reported alterations in TH and circadian rhythm in AD patients. Behavior, cognition, cerebral blood flow, and glucose consumption were correlated with TH deficits in AD patients. Whether thyroid dysfunctions and AD have a cause-effect relationship was inconclusive, however, the literature was able to provide enough data to corroborate a relationship between TH and AD. Although further studies are needed in this field, the current systematic review provides information that could help future investigations.

The Role of Thyroid Function in Alzheimer's Disease

The thyroid gland is crucial for the regulation of metabolism, growth, and development of various tissues, organs, systems, including the central nervous system. Recent studies have implicated the role of thyroid dysfunction in the etiology of Alzheimer's disease (AD), while AD leads to a significant increase in the prevalence of thyroid dysfunction. In this review, we have analyzed the role of thyroid function in the pathophysiology of AD as well as its biomarkers. The present review aims to provide encouraging targets for early screening of AD risk factors and intervention strategies.

The clinical use of blood-test factors for Alzheimer's disease: improving the prediction of cerebral amyloid deposition by the QPLEXTM Alz plus assay kit

Alzheimer's disease (AD) is the leading cause of dementia, and many studies have focused on finding effective blood biomarkers for the accurate diagnosis of this disease. Predicting cerebral amyloid deposition is considered the key for AD diagnosis because a cerebral amyloid deposition is the hallmark of AD pathogenesis. Previously, blood biomarkers were discovered to predict cerebral amyloid deposition, and further efforts have been made to increase their sensitivity and specificity. In this study, we analyzed blood-test factors (BTFs) that can be commonly measured in medical health check-ups from 149 participants with cognitively normal, 87 patients with mild cognitive impairment, and 64 patients with clinically diagnosed AD dementia with brain amyloid imaging data available. We demonstrated that four factors among regular health check-up blood tests, cortisol, triglyceride/high-density lipoprotein cholesterol ratio, alanine aminotransferase, and free triiodothyronine, showed either a significant difference by or correlation with cerebral amyloid deposition. Furthermore, we made a prediction model for Pittsburgh compound B-positron emission tomography positivity, using BTFs and the previously discovered blood biomarkers, the QPLEXTM Alz plus assay kit biomarker panel, and the area under the curve was significantly increased up to 0.845% with 69.4% sensitivity and 90.6% specificity. These results show that BTFs could be used as co-biomarkers and that a highly advanced prediction model for amyloid plaque deposition could be achieved by the combinational use of diverse biomarkers.

PD-1/PD-L1 affects Graves progression through lymphocytes on the proliferation, apoptosis and inflammatory cytokine secretion of thyroid follicular epithelial cells

We aimed to investigate the role of programmed cell death protein 1 (PD-1) and T lymphocytes in the proliferation, apoptosis and secretion of cells from patients and mice with Graves' disease (GD). The levels of serum hormones, related antibodies and inflammatory cytokines in GD patients were determined by electrochemiluminescence immunoassay and ELISA. The percentages of CD4 and CD8 T-lymphocytes and PD-1 expression were examined by flow cytometry. A GD mouse model, a thyroid follicular epithelial cell, and a CD4+PD-1+, CD4+PD-1- and CD8+PD-1+, CD8+PD-1- T lymphocyte co-culture system were constructed. The viability, apoptosis-related markers, serum hormones, related antibodies and inflammatory cytokines in thyroid follicular epithelial cells were determined by CCK-8, Western blot, qTR-PCR, electrochemiluminescence immunoassay and ELISA. Elevated free thyroid hormones (FT3, FT4), thyroid hormone antibodies (TRAb, TPOAb and TGAb), inflammatory cytokines, and inhibited TSH were observed in GD patients. The percentage of CD4⁺ T cells was increased, while that of CD8⁺ T cells was reduced in GD patients. PD-1 expression level was lifted in both CD4⁺ and CD8⁺ cells from GD patients. In mouse thyroid follicular epithelial cells co-cultured with CD4⁺PD-1⁺ and CD8⁺PD-1⁺ T lymphocytes, the cell viability, TH and TRAb levels and inflammatory cytokines level were the highest, while the TSH level and apoptosis were the lowest. PD-1 positive T lymphocytes were able to promote viability and inhibit apoptosis of thyroid follicular epithelial cells, which further caused a more accelerated development of GD.

Relationship Between Thyroid Hormone Levels and the Pathology of Alzheimer's Disease in Euthyroid Subjects

Background: Although several studies have reported an association between thyroid dysfunction and Alzheimer's disease (AD), the effect of mild thyroid dysfunction within the normal range of thyrotropin (TSH) on the development of AD remains unclear. The aim of this study was to evaluate the association between thyroid hormones and the pathology of AD in euthyroid subjects. Methods: Sixty-nine subjects with a TSH level between 0.5 and 4.5 μIU/L who underwent ¹⁸F-florbetaben positron emission tomography were included in this prospective cross-sectional study. The levels of serum free thyroxine (fT4) and TSH were quantified using radioimmunoassay. Neuropsychological tests were performed to assess cognitive function. Differences in cerebral amyloid-β (Aβ) burden were compared between high-normal TSH (TSH ≥2.5 μIU/mL) and low-normal TSH (TSH <2.5 μIU/mL) groups. Multiple linear regression analyses, adjusted for age, sex, education level, and Neuropsychiatric Inventory scores, were performed to evaluate relationships between thyroid hormone levels and both cerebral Aβ burden and cognitive function. Results: The cerebral Aβ burden in the high-normal TSH group was significantly higher than in the low-normal TSH group (1.53 ± 0.31 vs. 1.35 ± 0.22, p = 0.009). The fT4 levels were negatively correlated with cerebral Aβ burden (β = -0.240, p = 0.035), and TSH levels were positively correlated with cerebral Aβ burden (β = 0.267, p = 0.020). The fT4 level was also positively associated with cognitive function, as inferred from neuropsychological test scores. Conclusions: Thyroid hormone concentrations were associated with AD pathology in euthyroid subjects. Our findings suggest that AD is likely to occur even in individuals with high-normal TSH levels.

On the Etiopathogenesis and Pathophysiology of Alzheimer's Disease: A Comprehensive Theoretical Review

Alzheimers' disease (AD) is the most common cause of dementia, with an estimated 5 million new cases occurring annually. Among the elderly, AD shortens life expectancy, results in disability, decreases quality of life, and ultimately, leads to institutionalization. Despite extensive research in the last few decades, its heterogeneous pathophysiology and etiopathogenesis have made it difficult to develop an effective treatment and prevention strategy. Aging is the biggest risk factor for AD and evidence suggest that the total number of older people in the population is going to increase astronomically in the next decades. Also, there is evidence that air pollution and increasing income inequality may result in higher incidence and prevalence of AD. This makes the need for a comprehensive understanding of the etiopathogenesis and pathophysiology of the disease extremely critical. In this paper, a quintuple framework of thyroid dysfunction, vitamin D deficiency, sex hormones, and mitochondria dysfunction and oxidative stress are used to provide a comprehensive description of AD etiopathogenesis and pathophysiology. The individual role of each factor, their synergistic and genetic interactions, as well as the limitations of the framework are discussed.

Brain metabolic patterns in patients with suspected non-Alzheimer's pathophysiology (SNAP) and Alzheimer's disease (AD): is [18F] FDG a specific biomarker in these patients?

PURPOSE

The present study was conducted to compare the pattern of brain [¹⁸F] FDG uptake in suspected non-Alzheimer's pathophysiology (SNAP), AD, and healthy controls using 2-deoxy-2-[¹⁸F]fluoroglucose ([¹⁸F] FDG) positron emission tomography imaging. Cerebrospinal fluid (CSF) biomarkers amyloid-β1-42 peptide (Aβ1-42) and tau were used in order to differentiate AD from SNAP.

METHODS

The study included 43 newly diagnosed AD patients (female = 23; male = 20) according to the NINCDS-ADRDA criteria, 15 SNAP patients (female = 12; male =3), and a group of 34 healthy subjects that served as the control group (CG), who were found to be normal at neurological evaluation (male = 20; female = 14). A battery of neuropsychological tests was administrated in AD and SNAP subjects; cerebrospinal fluid assay was conducted in both AD and SNAP as well. Brain PET/CT acquisition was started 30 ± 5 min after [¹⁸F] FDG injection in all subjects. SPM12 [statistical parametric mapping] implemented in MATLAB 2018a was used for the analysis of PET scans in this study.

RESULTS

As compared to SNAP, AD subjects showed significant hypometabolism in a wide cortical area involving the right frontal, parietal, and temporal lobes. As compared to CG, AD subjects showed a significant reduction in [¹⁸F] FDG uptake in the parietal, limbic, and frontal cortex, while a more limited reduction in [¹⁸F] FDG uptake in the same areas was found when comparing SNAP to CG.

CONCLUSIONS

SNAP subjects show milder impairment of brain [¹⁸F] FDG uptake as compared to AD. The partial overlap of the metabolic pattern between SNAP and AD limits the use of [¹⁸F] FDG PET/CT in effectively discriminating these clinical entities.

The relationship between thyroid function and cerebral blood flow in mild cognitive impairment and Alzheimer's disease

The thyroid hormones have been reported to be associated with cognitive decline and Alzheimer’s disease. The relationship between thyroid function within the normal range and cerebral blood flow in Alzheimer’s disease patients has been shown in a recent study. Mild cognitive impairment is often the first stage of Alzheimer’s disease; thus, early diagnosis is important. The present study investigated the relationship between thyroid function and regional cerebral blood flow in patients with mild cognitive impairment and Alzheimer’s disease. A total of 122 memory clinic outpatients who underwent thyroid function testing and single photon emission computed tomography were divided into mild cognitive impairment, Alzheimer’s disease, and Normal groups. Regional cerebral blood flow was calculated using a three-dimensional stereotactic region of interest template in an automated cerebral perfusion single photon emission computed tomography analysis system. Multiple regression analysis adjusted for age and sex was conducted to examine the relationships between thyroid hormones and regional cerebral blood flow. Thyroid stimulating hormone was significantly associated with regional cerebral blood flow in the bilateral temporal, bilateral pericallosal, and bilateral hippocampal regions in the mild cognitive impairment group. In the Alzheimer’s disease group, free triiodothyronine was significantly associated with regional cerebral blood flow in the bilateral parietal, right temporal, and bilateral pericallosal regions. The present study showed the association of thyroid stimulating hormone with regional cerebral blood flow in the mild cognitive impairment group and the association of free triiodothyronine with regional cerebral blood flow in the Alzheimer’s disease group. These study findings could contribute to the early diagnosis of mild cognitive impairment at general memory clinics and the prevention of subsequent progression to Alzheimer’s disease.

Thyroid Hormone Enhances Neurite Outgrowth in Neuroscreen 1 Cells

Objectives

Alzheimer's disease (AD) is a neurodegenerative disorder that affects millions of individuals. Moreover, hypothyroidism has been identified as one of the risk factors that may contribute to the development of AD. Here, we investigated whether there was a correlation among expression levels of proteins involved in the formation of AD lesions, neurite outgrowth, and thyroid hormone levels.

Methods

Cells were grown in media supplemented with different levels of 3,5,3'-triiodothyronine (T3) and then processed for neurite outgrowth and to prepare RNA samples. RNA samples were analysed using quantitative real-time PCR. Protein levels were measured using in cell-Western blotting analysis.

Results

By using neurite outgrowth studies, it was demonstrated that T3 treatment enhanced neurite outgrowth in NS-1 cells in a time- and dose-dependent manner. Quantitative real-time PCR studies further confirmed that NS-1 cells expressed substantial levels of TRα and significantly less TRβ, either of which could be responsible for the T3-dependent effects on neurite outgrowth. Although the overall tau protein expression was not affected in response to T3 treatment, the splicing of tau exon 10 was impacted in the direction of producing more tau molecules that excluded the exon (tau 3R).

Conclusion

The results of this study are critical not only to understand the probable link between hypothyroidism and AD but also in providing the basis for future prevention and treatment of AD in hypothyroid patients.