Elevated Serum Tsukushi Levels in Patients With Hyperthyroidism

Association of serum Tsukushi level with metabolic syndrome and its components

PURPOSE

Tsukushi (TSK), a novel hepatokine, has recently been pointed out to play an important role in energy homeostasis and glycolipid metabolism. However, there are no clinical studies on the association of TSK with metabolic syndrome (MetS), the typical constellation of metabolic disorders. This study was conducted to explore the relationship between TSK and MetS as well as each of its metabolic component clinically.

METHODS

We analyzed in this cross-sectional study serum TSK levels by ELISA in 392 participants, including 90 non-MetS and 302 MetS, to compare TSK in two groups and in different numbers of metabolic components. The odds ratios (OR) of TSK quartile in MetS and each metabolic component were computed by multivariate logistic regression analysis.

RESULTS

TSK was substantially higher in MetS than in non-MetS subjects (P < 0.001). TSK increased with the concomitant increase of the number of metabolic components (P for <0.001). Logistic regression analyses demonstrated that the OR of MetS was 2.74 for the highest versus the lowest quartile of TSK (P < 0.001) after adjusting for age, gender, smoking status, alcohol consumption and medication use. Additionally, TSK was associated with the OR of poor HDL-C and elevated fasting glucose (P < 0.05).

CONCLUSION

Circulating TSK was higher in MetS patients and linked with MetS risk, suggesting that TSK may play a role in the genesis of MetS and be a potential therapeutic target for MetS. Future study should investigate the connection between TSK levels and MetS pathogenesis.

A review on Tsukushi: mammalian development, disorders, and therapy

Tsukushi (TSK), a leucine-rich peptidoglycan in the extracellular compartment, mediates multiple signaling pathways that are critical for development and metabolism. TSK regulates signaling pathways that eventually control cellular communication, proliferation, and cell fate determination. Research on TSK has become more sophisticated in recent years, illustrating its involvement in the physiology and pathophysiology of neural, genetic, and metabolic diseases. In a recent study, we showed that TSK therapy reversed the pathophysiological abnormalities of the hydrocephalic (a neurological disorder) brain in mice. This review summarizes the roles of TSK in key signaling processes in the mammalian development, disorders, and evaluating its possible therapeutic and diagnostic potential.

Plasma Tsukushi Concentration Is Associated with High Levels of Insulin and FGF21 and Low Level of Total Cholesterol in a General Population without Medication

Tsukushi (TSK) is a member of the small leucine-rich proteoglycan family that controls developmental processes and organogenesis. TSK was also identified as a new hepatokine, which is mainly expressed in the liver, and is secreted by hepatocytes, to regulate energy and glycolipid metabolism in response to nonalcoholic fatty liver disease. However, the role of plasma TSK, especially its role in the general population, has not been fully addressed. We investigated the associations between plasma TSK concentration and several metabolic markers, including fibroblast growth factor 21 (FGF21), a hepatokine, and adiponectin, an adipokine, in 253 subjects (men/women: 114/139) with no medication in the Tanno−Sobetsu Study, which employed a population-based cohort. There was no significant sex difference in plasma TSK concentration, and the level was positively correlated with the fatty liver index (FLI) (r = 0.131, p = 0.038), levels of insulin (r = 0.295, p < 0.001) and levels of FGF21 (r = 0.290, p < 0.001), and was negatively correlated with the total cholesterol level (r = −0.124, p = 0.049). There was no significant correlation between the TSK level and body mass index, waist circumference, adiponectin, high-density lipoprotein cholesterol or total bile acids. The multivariable regression analysis showed that high levels of insulin and FGF21 and a low level of total cholesterol were independent determinants of plasma TSK concentration, after adjustment for age, sex and FLI. In conclusion, plasma TSK concentration is independently associated with high levels of insulin and FGF21, a hepatokine, and a low level of total cholesterol, but not with adiposity and adiponectin, in a general population of subjects who have not taken any medications.

The hepatokine TSK maintains myofiber integrity and exercise endurance and contributes to muscle regeneration

Mammalian skeletal muscle contains heterogenous myofibers with different contractile and metabolic properties that sustain muscle mass and endurance capacity. The transcriptional regulators that govern these myofiber gene programs have been elucidated. However, the hormonal cues that direct the specification of myofiber types and muscle endurance remain largely unknown. Here we uncover the secreted factor Tsukushi (TSK) as an extracellular signal that is required for maintaining muscle mass, strength, and endurance capacity, and contributes to muscle regeneration. Mice lacking TSK exhibited reduced grip strength and impaired exercise capacity. Muscle transcriptomic analysis revealed that TSK deficiency results in a remarkably selective impairment in the expression of myofibrillar genes characteristic of slow-twitch muscle fibers that is associated with abnormal neuromuscular junction formation. AAV-mediated overexpression of TSK failed to rescue these myofiber defects in adult mice, suggesting that the effects of TSK on myofibers are likely restricted to certain developmental stages. Finally, mice lacking TSK exhibited diminished muscle regeneration following cardiotoxin-induced muscle injury. These findings support a crucial role of TSK as a hormonal cue in the regulation of contractile gene expression, endurance capacity, and muscle regeneration.

Newly discovered endocrine functions of the liver

The liver, the largest solid visceral organ of the body, has numerous endocrine functions, such as direct hormone and hepatokine production, hormone metabolism, synthesis of binding proteins, and processing and redistribution of metabolic fuels. In the last 10 years, many new endocrine functions of the liver have been discovered. Advances in the classical endocrine functions include delineation of mechanisms of liver production of endocrine hormones [including 25-hydroxyvitamin D, insulin-like growth factor 1 (IGF-1), and angiotensinogen], hepatic metabolism of hormones (including thyroid hormones, glucagon-like peptide-1, and steroid hormones), and actions of specific binding proteins to glucocorticoids, sex steroids, and thyroid hormones. These studies have furthered insight into cirrhosis-associated endocrinopathies, such as hypogonadism, osteoporosis, IGF-1 deficiency, vitamin D deficiency, alterations in glucose and lipid homeostasis, and controversially relative adrenal insufficiency. Several novel endocrine functions of the liver have also been unraveled, elucidating the liver’s key negative feedback regulatory role in the pancreatic α cell-liver axis, which regulates pancreatic α cell mass, glucagon secretion, and circulating amino acid levels. Betatrophin and other hepatokines, such as fetuin-A and fibroblast growth factor 21, have also been discovered to play important endocrine roles in modulating insulin sensitivity, lipid metabolism, and body weight. It is expected that more endocrine functions of the liver will be revealed in the near future.

Serum Tsukushi levels are elevated in newly diagnosed type 2 diabetic patients

AIMS

Tsukushi, a newly identified hepatokine, has been recently characterized as a potent modifier in lipid metabolism and energy homeostasis, but the role of Tsukushi in diabetes remains almost unknown. We detected for the first time the serum Tsukushi levels in newly diagnosed type 2 diabetes, exploring the relationship between Tsukushi and various metabolic parameters.

METHODS

A total of 172 participants were recruited, including 86 patients with newly diagnosed type 2 diabetes and 86 subjects with normal glucose tolerance according to oral glucose tolerance test. Serum Tsukushi was measured by ELISA. The insulin resistance, pancreas β-cell function and insulin sensitivity were determined by homeostasis model assessment (HOMA-IR, HOMA-β), Stumvoll insulin sensitivity index (ISI_stumvoll) and Stumvoll metabolic clearance rate (MCR_stumvoll).

RESULTS

Serum Tsukushi was significantly higher in type 2 diabetes than in normal glucose tolerance [1.22(0.86,1.74) vs 0.8(0.5,1.38) ng/mL; P < 0.001]. Multiple regression analysis showed that BMI, 2-h post-OGTT glucose and TC were independently related factors influencing Tsukushi. Logistic regression analyses demonstrated that Tsukushi was associated with higher risk of type 2 diabetes independently.

CONCLUSIONS

Circulating Tsukushi levels significantly increase in patients with type 2 diabetes, which suggest that Tsukushi may play a role in type 2 diabetes pathogenesis.