Yoshiyuki Sakai

Abstract Background We aimed to elucidate the relationship between serum myostatin levels and other markers including skeletal muscle mass and to investigate the influence of serum myostatin levels on survival for patients with liver cirrhosis (LC). Methods A total of 198 LC subjects were analysed in this study. Myostatin levels were measured using stored sera. We retrospectively investigated the relationship between myostatin level and other markers, and the influence of myostatin level on overall survival (OS). Assessment of skeletal muscle mass was performed using the psoas muscle index (PMI) on computed tomography images at baseline. PMI indicates the sum of bilateral psoas muscle mass calculated by hand tracing at the lumber three level on computed tomography images divided by height squared (cm 2 /m 2 ). The study cohort was divided into two groups based on the median myostatin value in each gender. Results Our study cohort included 108 male and 90 female patients with a median age of 67.5 years. The median (range) myostatin level for male patients was 3419.6 pg/mL (578.4–12897.7 pg/mL), whereas that for female patients was 2662.4 pg/mL (710.4–8782.0 pg/mL) ( P = 0.0024). Median (range) serum myostatin level for Child–Pugh A patients ( n = 123) was 2726.0 pg/mL (578.4–12667.2 pg/mL), whereas that for Child–Pugh B or C patients ( n = 75) was 3615.2 pg/mL (663.3–12897.7 pg/mL) ( P = 0.0011). For the entire cohort, the 1‐, 3‐, 5‐, and 7‐year cumulative OS rates were 93.94%, 72.71%, 50.37%, and 38.47%, respectively, in the high‐myostatin group and 96.97%, 83.27%, 73.60%, and 69.95%, respectively, in the low‐myostatin group ( P = 0.0001). After excluding hepatocellular carcinoma patients (at baseline) from our analysis ( n = 158), the 1‐, 3‐, 5‐, and 7‐year cumulative OS rates were 96.0%, 77.93%, 52.97%, and 39.08%, respectively, in the high‐myostatin group and 96.39%, 87.58%, 77.63%, and 73.24%, respectively, in the low‐myostatin group ( P = 0.0005). Higher age ( P = 0.0111) and lower PMI ( P < 0.0001) were identified as significant predictors of poorer OS in our multivariate analysis, while higher serum myostatin ( P = 0.0855) tended to be a significant adverse predictor. In both genders, PMI, serum albumin, prothrombin time, and branched‐chain amino acid to tyrosine ratio showed a significantly inverse correlation with myostatin levels, and serum ammonia levels showed a significantly positive correlation with myostatin levels. Conclusions Higher serum myostatin levels correlated with muscle mass loss, hyperammonemia, and impaired protein synthesis, as reflected by lower serum albumin levels and lower branched‐chain amino acid to tyrosine ratio levels. High serum myostatin levels were also associated with a reduced OS rate in LC patients.

The 25-hydroxyvitamin D-24-hydroxylase (CYP24A1) plays an important role in regulating concentrations of both the precursor 25-hydroxyvitamin D3 [25(OH)D3] and the hormone 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)(2)D3]. Previous studies suggest that Cyp24a1-null mice cannot clear exogenous 1alpha,25(OH)2D3 efficiently. Here, we examined the metabolic clearance in Cyp24a1-null mice in vivo and in vitro using a physiological dose of [1beta-3H]1alpha,25(OH)2D3 or [26,27-methyl-3H]25(OH)D3. Cyp24a1-null mice showed difficulty in eliminating [1beta-3H]1alpha,25(OH)2D3 from the bloodstream and tissues over a 96-h time course, whereas heterozygotic mice eliminated the hormone within 6-12 h, although there was clearance of labeled hormone into water-soluble products involving liver in both genotypes. RT-PCR showed that Cyp24a1-null mice have decreased expression of 25-hydroxyvitamin D-1alpha-hydroxylase that must play a role in their survival. After the administration of [26,27-methyl-3H]25(OH)D3, Cyp24a1-null mice showed higher [26,27-methyl-3H]25(OH)D3 levels and no [26,27-methyl-3H]24,25(OH)2D3 formation, whereas heterozygotic mice showed significant [26,27-methyl-3H]24,25(OH)2D3 production. Based upon in vitro experiments, keratinocytes from Cyp24a1-null mice fail to synthesize [1beta-3H]calcitroic acid from [1beta-3H]1alpha,25(OH2D3 or [26,27-methyl-3H]24,25(OH)2D3 from [26,27-methyl-3H]25(OH)D3 as do control mice, confirming the target cell catabolic role of CYP24A1 in these processes. Finally, the role of vitamin D receptor (VDR) in the vitamin D catabolic cascade was examined using VDR-null mice. Keratinocytes from VDR-null mice failed to metabolize [1beta-3H]1alpha,25(OH)2D3 confirming the importance of vitamin D-inducible, VDR-mediated, C24 oxidation pathway in target cells. These results suggest that the absence of CYP24A1 or VDR retards catabolism of 1alpha,25(OH)2D3 and 25(OH)D3, reinforcing the physiological importance of CYP24A1 in vitamin D homeostasis.

Targeted ablation of the vitamin D receptor (VDR) results in hypocalcemia, hypophosphatemia, hyperparathyroidism, rickets, osteomalacia, and alopecia--the last a consequence of defective anagen initiation. To investigate whether the markedly elevated levels of 1,25-dihydroxyvitamin D led to the alopecia, we raised VDR-null mice in a ultraviolet light-free environment and fed them chow lacking vitamin D for five generations. Despite undetectable circulating levels of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D, alopecia persisted in the VDR-null mice, demonstrating that the alopecia was not secondary to toxic levels of 1,25-dihydroxyvitamin D interacting with an alternative receptor. Furthermore, alopecia was not seen in control littermates, suggesting that absence of ligand and absence of receptor cause different phenotypes. To identify the cell population responsible for the alopecia, we performed hair-reconstitution assays in nude mice and observed normal hair follicle morphogenesis, regardless of the VDR status of the keratinocytes and dermal papilla cells. However, follicles reconstituted with VDR-null keratinocytes demonstrated a defective response to anagen initiation. Hence, alopecia in the VDR-null mice is due to a defect in epithelial-mesenchymal communication that is required for normal hair cycling. Our results also identify the keratinocyte as the cell of origin of the defect and suggest that this form of alopecia is due to absence of ligand-independent receptor function.

Vitamin D receptor (VDR) null mice develop hypocalcemia, hyperparathyroidism, rickets, osteomalacia and alopecia. Normalization of mineral ion homeostasis prevents all of these abnormalities except alopecia. Hair reconstitution assays, performed in athymic nude mice, demonstrate that the lack of VDR in keratinocytes leads to a defect in anagen initiation, similar to that observed in VDR null mice. Although these studies demonstrate that expression of the VDR in keratinocytes is necessary, they do not prove that it is sufficient for maintenance of the normal hair cycle. To address this hypothesis, we generated transgenic mice expressing the human VDR under the control of the keratin 14 (K14) promoter. Two highly expressing transgenic lines were mated with VDR null mice to obtain VDR null mice expressing the human VDR transgene (hVDR+/mVDR-). Expression of the transgene in the VDR null mice prevented alopecia. Furthermore, when subjected to anagen initiation, the hair follicle keratinocytes of the hVDR+/mVDR- mice demonstrated an enhanced proliferative response compared to those of control littermates. Restoration of VDR expression in the keratinocytes of VDR null mice, prevents the hair cycle defect that leads to the development of alopecia.