The MATP/tau protein is hyperphosphorylated in Alzheimer’s patients. Therefore, research into the regulation of tau protein phosphorylation is important for understanding Alzheimer’s disease. HASPIN is a serine/threonine kinase that is expressed in various cells. To examine whether HASPIN is involved in the onset of Alzheimer’s disease through tau protein phosphorylation, we investigated the effects of a diet including soybean sprouts rich in the HASPIN inhibitor coumestrol in a mouse model of Alzheimer’s disease (5xFAD). The results showed that HASPIN was expressed in the hippocampus and phosphorylated tau protein, while the ingestion of soybean sprouts containing coumestrol suppressed the development of spatial cognitive dysfunction in 5xFAD. These results indicate that HASPIN may be one of the target molecules for the repression of tau phosphorylation in the treatment of Alzheimer’s disease.

Transthyretin (TTR) is an amyloidogenic protein associated with hereditary and nonhereditary transthyretin amyloidoses (ATTR). Dissociation of the tetramer of TTR to the monomer induces TTR misfolding, which leads to amyloid fibril formation and triggers the onset of ATTR amyloidosis. Stabilizers of tetrameric TTR have been accepted as an effective ATTR amyloidosis treatment while effect is limited and they are too expensive. The aim of our study was to find more effective and cheep natural compound to suppress TTR amyloid formation. Glabridin, a prenylated isoflavan isolated from Glycyrrhiza glabra L., stabilized the TTR tetramer in vitro. The effects of licorice-derived flavonoid oil—Glavonoid, a natural substance that includes glabridin and several polyphenols—on stabilizing the TTR tetramer must still be elucidated. To examine plasma TTR stabilization by Glavonoid in vitro, we investigated the feasibility of utilizing glabridin plus Glavonoid to prevent TTR amyloid fibril formation. Glavonoid mixed with human plasma samples at 24 h incubation in vitro increased the tetramer level (P < 0.05) and reduced the monomer level (P < 0.01) and the monomer/tetramer ratio (P < 0.05) of TTR compared to those without Glavonoid by immunoblot analysis, such effect could not observe in the presence of glabridin. Oral Glavonoid (300 mg for 12 weeks) in 7 healthy volunteers effectively increased the plasma glabridin concentration. Glavonoid increased the TTR tetramer level and reduced the monomer/tetramer ratio of TTR (P < 0.05) in plasma at 12 weeks in healthy volunteers compared to those of age matched control subjects without the supplement. Thus, oral Glavonoid may effectively prevent TTR amyloid fibril formation via TTR tetramer stabilization. Glavonoid may become a promising supplement before onset of ATTR amyloidosis.

We previously demonstrated that the Alzheimer’s disease (AD)-like model mice, Tg2576, housed at a high ambient temperature of 30 °C for 13 months, exhibited increased body temperature, which increased amyloid-β (Aβ) levels and tau stability, leading to tau phosphorylation and ultimately inducing memory impairment. Here, we aimed to exclude the possible effect of environmental factors associated with the difference in ambient temperature (23 °C vs. 30 °C) and to further clarify the effects of elevated body temperature on AD-like pathologies. We generated uncoupling protein 1 (UCP1) deletion in Tg2576 mice, Tg2576/UCP1^−/−, because UCP1 deletion mice show a sustained rise in body temperature at normal room temperature. As expected, the body temperature in Tg2576/UCP1^−/− mice was higher than that in Tg2576/ UCP1^+/+ mice at 23 °C, which was accompanied by upregulated Aβ levels due to increased β-secretase (BACE1) and decreased neprilysin (NEP) protein levels in the brains of Tg2576/UCP1^−/− mice compared with those in the Tg2576/ UCP1^+/+ mice. Elevated body temperature also increased total tau levels, leading to enhanced phosphorylation, heat shock protein induction, and activated tau kinases. Furthermore, elevated body temperature enhanced glial activation and decreased synaptic protein levels in the brain. Taken together, these findings demonstrate that elevated body temperatures exacerbate AD-like pathologies.

Transthyretin (TTR) is an amyloidogenic protein associated with TTR amyloidosis (ATTR). Dissociation of TTR tetramers into TTR monomers causes TTR misfolding, resulting in amyloid fibril formation and triggering the onset of ATTR. Low-molecular-weight tetrameric TTR stabilizers are potential therapeutic agents to delay ATTR progression. However, the currently available drugs are expensive and cannot be used for prophylaxis. Therefore, in this study, we aimed to identify a prophylactic supplement that suppresses TTR amyloid formation. We investigated whether arginine, an amyloidogenic protein aggregation inhibitor, stabilizes tetrameric TTR, thereby preventing amyloid fibril formation. Immunoblotting showed that arginine mixed with wild-type TTR (TTRwt), amyloidogenic TTR Val30Met (ATTR V30M), and human serum samples reduced the amount of monomeric TTR but increased the tetramer/monomer ratio of TTR compared to those in the samples without arginine. Additionally, oral administration of arginine (5000 mg for 5 days) to healthy volunteers effectively increased the tetramer/monomer ratio of TTR in the serum. Thioflavin T test, a quantitative analysis method for amyloid fibril formation, showed that amyloid fibril formation was significantly suppressed with arginine compared to that without arginine. As arginine is a common supplement and non-toxic amino acid, it can be used as a promising prophylactic supplement to suppress amyloid fibril formation in ATTR.

In the future, humans may live in space because of global pollution and weather fluctuations. In microgravity, convection does not occur, which may change the amyloidogenicity of proteins. However, the effect of gravity on amyloid fibril formation is unclear and remains to be elucidated. Here, we analyzed the effect of microgravity on amyloid fibril formation of amyloidogenic proteins including insulin, amyloid β42 (Aβ42), and transthyretin (TTR). We produced microgravity (10−3 g) by using the gravity controller Gravite. Human insulin, Aβ42, and human wild-type TTR (TTRwt) were incubated at pH 3.0, 7.0, and 3.5 at 37 °C, respectively, in 1 g on the ground or in microgravity. We measured amyloidogenicity via the thioflavin T (ThT) method and cell-based 1-fluoro-2,5-bis[(E)-3-carboxy-4-hydroxystyryl]benzene (FSB) assay. ThT fluorescence intensity and cell-based FSB assay results for human insulin samples were decreased in microgravity compared with results in 1 g. Aβ42 samples did not differ in ThT fluorescence intensity in microgravity and in 1 g on the ground. However, in the cell-based FSB assay, the staining intensity was reduced in microgravity compared with that on 1 g. Human TTRwt tended to form fewer amyloid fibrils in ThT fluorescence intensity and cell-based FSB assays in microgravity than in 1 g. Human insulin and Aβ42 showed decreased amyloid fibril formation in microgravity compared with that in 1 g. Human TTRwt tended to form fewer amyloid fibrils in microgravity. Our experiments suggest that the earth's gravity may be an accelerating factor for amyloid fibril formation.

Transthyretin (TTR), the precursor protein for amyloidogenic TTR (ATTR) amyloidosis, forms tetramers and escapes glomerular filtration by binding with thyroxine and retinol-binding protein. However, variant TTRs are unstable as tetramers, so monomeric TTR has become the precursor protein of amyloid deposits, via protein misfolding. The aim of the study was to evaluate the utility of urinary TTR in the diagnosis of ATTRv amyloidosis. Urinary samples from healthy volunteers, ATTRv V50M amyloidosis patients, and asymptomatic carriers of the ATTRv V50M gene were analysed using ELISA. To analyse the different forms of TTR secreted to the urine, we performed Western blotting and mass spectrometry. Urinary TTR concentrations were significantly higher in the ATTRv V50M amyloidosis patients than they were in the healthy volunteers and asymptomatic carriers of the gene. Although the TTR concentrations were negligible in the healthy volunteers, they were correlated with disease progression and urinary albumin concentrations in the ATTRv V50M amyloidosis patients. The Western blotting and mass spectrometry revealed the presence of monomeric wild-type and variant TTRs in the urine. Urinary TTR concentrations may become a more sensitive biomarker of ATTRv progression than albumin.