The Inhibitory Effect of Salmon Calcitonin on Tri-Iodothyronine Induction of Early Hypertrophy in Articular Cartilage

Salmon calcitonin has chondroprotective effect both in vitro and in vivo, and is therefore being tested as a candidate drug for cartilage degenerative diseases. Recent studies have indicated that different chondrocyte phenotypes may express the calcitonin receptor (CTR) differentially. We tested for the presence of the CTR in chondrocytes from tri-iodothyronin (T3)-induced bovine articular cartilage explants. Moreover, investigated the effects of human and salmon calcitonin on the explants.Early chondrocyte hypertrophy was induced in bovine articular cartilage explants by stimulation over four days with 20 ng/mL T3. The degree of hypertrophy was investigated by molecular markers of hypertrophy (ALP, IHH, COLX and MMP13), by biochemical markers of cartilage turnover (C2M, P2NP and AGNxII) and histology. The expression of the CTR was detected by qPCR and immunohistochemistry. T3-induced explants were treated with salmon or human calcitonin. Calcitonin down-stream signaling was measured by levels of cAMP, and by the molecular markers.Compared with untreated control explants, T3 induction increased expression of the hypertrophic markers (p<0.05), of cartilage turnover (p<0.05), and of CTR (p<0.01). Salmon, but not human, calcitonin induced cAMP release (p<0.001). Salmon calcitonin also inhibited expression of markers of hypertrophy and cartilage turnover (p<0.05).T3 induced early hypertrophy of chondrocytes, which showed an elevated expression of the CTR and was thus a target for salmon calcitonin. Molecular marker levels indicated salmon, but not human, calcitonin protected the cartilage from hypertrophy. These results confirm that salmon calcitonin is able to modulate the CTR and thus have chondroprotective effects

Fold expression (mean(95%CI)) of pre-hypertrophic marker in response to 1 and 10 nM sCT stimulation of T3-induced explants compared with T3-induced alone (T3).

§<p>P-value of ANOVA test,</p>#<p>P-value of Dunnett’s post-test.</p

Immunolocalization of the calcitonin receptor (CTR) in cartilage explants induced with or without T3 for 4 days.

<p>First panel shows the superficial layer of the cartilage, second panel the mid layer of the cartilage and the third panel the deep layer of the cartilage. Treatment scheme is indicated at the top of the pictures. The pictures are representative of 3 replicates from the same experiment. Positive staining is visualized by brown color.</p

Expression and induction of the calcitonin receptor (CTR) as a result of T3 stimulation.

<p>The level of cAMP produced by the chondrocytes two hours after application of A) salmon calcitonin (sCT) or B) human calcitonin (hCT). The measurements were taken at day 0, 4 and 8 in explants with or without T3. The measurements were normalized to vehicle control for each time point, giving the fold induction. Significance level; *p<0.05, and ***p<0.001, data shown as geometric mean with 95%-CI (N = 2, n = 10).</p

The effect of T3 stimulation on chondrocyte morphology in articular cartilage explants after 4 days of T3 administration.

<p>A) Control section (w/o) (n = 2). B) T3-induced explant (n = 4). C) Measurement of the perimeter in cells of the deep zone.</p

List of primer sequences applied in quantitative PCR analysis.

<p>List of primer sequences applied in quantitative PCR analysis.</p