The roles of sclerostin and irisin on bone and muscle of orchiectomized rats

Abstract

Background: The reduction in androgen level gives rise to a decrease in bone mineral density (BMD) and muscle strength, but the exact mechanisms are unclear. We investigated the roles of novel cytokines of sclerostin and irisin on bone and muscle of orchiectomized rats.

Methods: Twenty 3-month-old male rats were randomized to receive sham or orchiectomy (ORX) operation. Rats were euthanized after 8 weeks of surgery, and serum levels of sclerostin and irisin were measured by enzyme-linked immunosorbent assay at baseline and execution. Grip strength was measured by a grip strength tester at baseline and before execution. BMD and bone microarchitecture were measured by microcomputed tomography. The samples of bone and muscle were harvested at execution. Bone biomechanics were measured by three-point bending tests and vertebral body indentation tests. Bone and muscle histological features were analyzed by hematoxylin and eosin stain, Von Kossa's stain and tartrate resistant acid phosphatase stain. Simple linear regression analyses were used to analyze the relationships between serum levels of sclerostin, irisin and grip strength and BMD of ORX rats.

Results: Serum sclerostin level increased from 279 ± 44 pg/mL to 586 ± 57 pg/mL since baseline to 8 weeks after ORX (P = 0.002), which was significantly higher than that in sham rats (406 ± 20 pg/mL at execution) (P = 0.012). Serum irisin level decreased from 4.12 ± 0.20 ng/mL to 3.55 ± 0.29 ng/mL since baseline to 8 weeks of ORX (P = 0.048), which was significantly lower than sham rats (4.84 ± 0.37 pg/mL at execution) (P = 0.013). Trabecular BMD, parameters of bone microarchitecture, bone strength, grip strength and the myofibers size of soleus muscles were significantly lower in ORX rats than in sham group. Grip strength was positively correlated with femoral trabecular BMD (r = 0.713, P < 0.001) and bone volume/total volume (r = 0.712, P < 0.001) in all rats. The serum sclerostin level was negatively correlated to femoral trabecular BMD (r = -0.508, P = 0.022) and grip strength (r = -0.492, P = 0.028). Serum irisin level was positively correlated with femoral trabecular BMD (r = 0.597, P = 0.005), but no obvious correlation was found between irisin level and muscle strength in all rats.

Conclusions: Reduced BMD, impaired bone microarchitecture, weak strength of bone and muscle, and thin myofibers were induced by androgen deficiency of ORX rats. Serum sclerostin and irisin levels were significantly changed after ORX, which might be closely correlated with the occurrence of osteoporosis and sarcopenia in ORX rats.

Keywords: Irisin; Orchiectomy; Osteoporosis; Sarcopenia; Sclerostin.

Fig. 1

Change of serum sclerostin and irisin levels after ORX or sham operation. a Change of serum sclerostin levels in ORX and sham groups. b Change of serum irisin levels in the ORX and sham groups. *: P < 0.05 ORX vs the sham group after 8 weeks of operation. #: P < 0.05 vs baseline. Data expressed as mean ± standard error of the mean (SEM). Abbreviations: ORX: orchiectomy

Fig. 2

Bone histological characteristics of ORX and sham rats. a Von Kossa’s staining of the femur and the L3-4 in the ORX and sham group. b H&E staining of the femur and the L3-4 in the ORX and sham group. c TRAP staining of the femur and the L3-4 in the ORX and sham group. Scale bars indicate 500 µm. Arrows indicate the osteoblasts. Abbreviations: H&E: hematoxylin and eosin; TRAP: tartrate resistant acid phosphatase; ORX: orchiectomy

Fig. 3

Grip strength and muscle histological results. a YLS-13A grip strength tester. b Grip strength of ORX and sham rats at baseline and before execution. c H&E staining of the soleus muscle in the ORX and sham group. d Cross-sectional area of the soleus muscle in the ORX and sham group. *: P < 0.05 ORX vs the sham group after 8 weeks of operation. #: P < 0.05 vs baseline. Data expressed as mean ± standard error of the mean (SEM). Scale bars indicate 50 µm. Abbreviations: ORX: orchiectomy

Fig. 4

Correlations between sclerostin, irsin and muscle and bone after 8 weeks of ORX or sham operation. a Correlation between grip strength and BMD in total rats or ORX or sham rats. b Correlation between grip strength and BV/TV in total rats or ORX or sham rats. Abbreviations: BMD: bone mineral density; BV/TV: bone volume per total volume; ORX: orchiectomy

Fig. 5

Correlations between serum sclerostin and irisin level with grip strength and BMD aftre 8 weeks of ORX or sham operation. a Correlation between serum sclerostin level and BMD total rats. b Correlation between serum sclerostin level and grip strength in total rats. c Correlation between serum irisin level and BMD in total rats. d Correlation between serum irisin level and grip strength in total rats. Abbreviations: BMD: bone mineral density; BV/TV: bone volume per total volume; ORX: orchiectomy