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Thyrostimulin Regulates Osteoblastic Bone Formation During Early Skeletal Development.

Bassett JH, van der Spek A, Logan JG, Gogakos A, Bagchi-Chakraborty J, Murphy E, van Zeijl C, Down J, Croucher PI, Boyde A, Boelen A, Williams GR - Endocrinology (2015)

Bottom Line: However, thyrostimulin failed to induce a canonical cAMP response or activate the noncanonical Akt, ERK, or mitogen-activated protein kinase (P38) signaling pathways in primary calvarial or bone marrow stromal cell-derived osteoblasts.Furthermore, thyrostimulin did not directly inhibit osteoblast proliferation, differentiation or mineralization in vitro.These studies identify thyrostimulin as a negative but indirect regulator of osteoblastic bone formation during skeletal development.

View Article: PubMed Central - PubMed

Affiliation: Molecular Endocrinology Laboratory (J.H.D.B., J.G.L., A.G., J.B.C., E.M., G.R.W.), Department of Medicine, Imperial College London, London, W12 0NN United Kingdom; Department of Endocrinology (A.v.d.S., C.v.Z., A.Boe.), Academic Medical Centre, University of Amsterdam, 1100 DD Amsterdam, The Netherlands; Bone Biology Program (J.D., P.I.C.), Garvan Institute of Medical Research, Sydney, NSW 2010 Australia; and Centre for Oral Growth and Development (A.Boy.), Queen Mary, University of London, London, E1 4NS United Kingdom.

ABSTRACT
The ancestral glycoprotein hormone thyrostimulin is a heterodimer of unique glycoprotein hormone subunit alpha (GPA)2 and glycoprotein hormone subunit beta (GPB)5 subunits with high affinity for the TSH receptor. Transgenic overexpression of GPB5 in mice results in cranial abnormalities, but the role of thyrostimulin in bone remains unknown. We hypothesized that thyrostimulin exerts paracrine actions in bone and determined: 1) GPA2 and GPB5 expression in osteoblasts and osteoclasts, 2) the skeletal consequences of thyrostimulin deficiency in GPB5 knockout (KO) mice, and 3) osteoblast and osteoclast responses to thyrostimulin treatment. Gpa2 and Gpb5 expression was identified in the newborn skeleton but declined rapidly thereafter. GPA2 and GPB5 mRNAs were also expressed in primary osteoblasts and osteoclasts at varying concentrations. Juvenile thyrostimulin-deficient mice had increased bone volume and mineralization as a result of increased osteoblastic bone formation. However, thyrostimulin failed to induce a canonical cAMP response or activate the noncanonical Akt, ERK, or mitogen-activated protein kinase (P38) signaling pathways in primary calvarial or bone marrow stromal cell-derived osteoblasts. Furthermore, thyrostimulin did not directly inhibit osteoblast proliferation, differentiation or mineralization in vitro. These studies identify thyrostimulin as a negative but indirect regulator of osteoblastic bone formation during skeletal development.

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Dynamic and static histomorphometry. A, Confocal laser scanning microscopy (CLSM) images of calcein double labeled trabecular bone from P42 WT and GPB5KO mice. Scale bar, 50 μm. Two-dimensional quantitative analysis of mineralizing perimeter (MS/B.Pm), MAR, and BFR (BFR/B.Pm) (mean ± SEM). B, Proximal tibia trabecular bone sections from P42 WT and GPB5KO mice stained for TRAP activity. Arrows indicate TRAP positive osteoclasts. Scale bar, 100 μm. Two-dimensional quantitative analysis of the trabecular B.Pm, Oc.S/B.Pm, Oc.N/B.Pm, and the mean osteoclast perimeter (Oc.Pm). Student's t test, GPB5KO vs WT; *, P < .05; **, P < .01 (n = 3–5 per genotype, per gender, per age).
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Figure 6: Dynamic and static histomorphometry. A, Confocal laser scanning microscopy (CLSM) images of calcein double labeled trabecular bone from P42 WT and GPB5KO mice. Scale bar, 50 μm. Two-dimensional quantitative analysis of mineralizing perimeter (MS/B.Pm), MAR, and BFR (BFR/B.Pm) (mean ± SEM). B, Proximal tibia trabecular bone sections from P42 WT and GPB5KO mice stained for TRAP activity. Arrows indicate TRAP positive osteoclasts. Scale bar, 100 μm. Two-dimensional quantitative analysis of the trabecular B.Pm, Oc.S/B.Pm, Oc.N/B.Pm, and the mean osteoclast perimeter (Oc.Pm). Student's t test, GPB5KO vs WT; *, P < .05; **, P < .01 (n = 3–5 per genotype, per gender, per age).

Mentions: Static and dynamic histomorphometry was performed to investigate the cellular basis underlying the increased bone volume and mineralization in juvenile GPB5KO mice. Bone formation parameters were determined in samples from calcein double-labeled mice (Figure 6A). In juvenile female GPB5KO mice MAR (double calcein label separation divided by time between administration of labels) was increased by 26% and BFR (MAR multiplied by length of mineralizing surface) by 55%. In juvenile male GPB5KO mice, mineralizing surfaces were increased 27%, and BFR showed a similar trend to females. By contrast, osteoclastic bone resorption parameters did not differ among GPB5KO and WT mice (Figure 6B).


Thyrostimulin Regulates Osteoblastic Bone Formation During Early Skeletal Development.

Bassett JH, van der Spek A, Logan JG, Gogakos A, Bagchi-Chakraborty J, Murphy E, van Zeijl C, Down J, Croucher PI, Boyde A, Boelen A, Williams GR - Endocrinology (2015)

Dynamic and static histomorphometry. A, Confocal laser scanning microscopy (CLSM) images of calcein double labeled trabecular bone from P42 WT and GPB5KO mice. Scale bar, 50 μm. Two-dimensional quantitative analysis of mineralizing perimeter (MS/B.Pm), MAR, and BFR (BFR/B.Pm) (mean ± SEM). B, Proximal tibia trabecular bone sections from P42 WT and GPB5KO mice stained for TRAP activity. Arrows indicate TRAP positive osteoclasts. Scale bar, 100 μm. Two-dimensional quantitative analysis of the trabecular B.Pm, Oc.S/B.Pm, Oc.N/B.Pm, and the mean osteoclast perimeter (Oc.Pm). Student's t test, GPB5KO vs WT; *, P < .05; **, P < .01 (n = 3–5 per genotype, per gender, per age).
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Related In: Results  -  Collection

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Figure 6: Dynamic and static histomorphometry. A, Confocal laser scanning microscopy (CLSM) images of calcein double labeled trabecular bone from P42 WT and GPB5KO mice. Scale bar, 50 μm. Two-dimensional quantitative analysis of mineralizing perimeter (MS/B.Pm), MAR, and BFR (BFR/B.Pm) (mean ± SEM). B, Proximal tibia trabecular bone sections from P42 WT and GPB5KO mice stained for TRAP activity. Arrows indicate TRAP positive osteoclasts. Scale bar, 100 μm. Two-dimensional quantitative analysis of the trabecular B.Pm, Oc.S/B.Pm, Oc.N/B.Pm, and the mean osteoclast perimeter (Oc.Pm). Student's t test, GPB5KO vs WT; *, P < .05; **, P < .01 (n = 3–5 per genotype, per gender, per age).
Mentions: Static and dynamic histomorphometry was performed to investigate the cellular basis underlying the increased bone volume and mineralization in juvenile GPB5KO mice. Bone formation parameters were determined in samples from calcein double-labeled mice (Figure 6A). In juvenile female GPB5KO mice MAR (double calcein label separation divided by time between administration of labels) was increased by 26% and BFR (MAR multiplied by length of mineralizing surface) by 55%. In juvenile male GPB5KO mice, mineralizing surfaces were increased 27%, and BFR showed a similar trend to females. By contrast, osteoclastic bone resorption parameters did not differ among GPB5KO and WT mice (Figure 6B).

Bottom Line: However, thyrostimulin failed to induce a canonical cAMP response or activate the noncanonical Akt, ERK, or mitogen-activated protein kinase (P38) signaling pathways in primary calvarial or bone marrow stromal cell-derived osteoblasts.Furthermore, thyrostimulin did not directly inhibit osteoblast proliferation, differentiation or mineralization in vitro.These studies identify thyrostimulin as a negative but indirect regulator of osteoblastic bone formation during skeletal development.

View Article: PubMed Central - PubMed

Affiliation: Molecular Endocrinology Laboratory (J.H.D.B., J.G.L., A.G., J.B.C., E.M., G.R.W.), Department of Medicine, Imperial College London, London, W12 0NN United Kingdom; Department of Endocrinology (A.v.d.S., C.v.Z., A.Boe.), Academic Medical Centre, University of Amsterdam, 1100 DD Amsterdam, The Netherlands; Bone Biology Program (J.D., P.I.C.), Garvan Institute of Medical Research, Sydney, NSW 2010 Australia; and Centre for Oral Growth and Development (A.Boy.), Queen Mary, University of London, London, E1 4NS United Kingdom.

ABSTRACT
The ancestral glycoprotein hormone thyrostimulin is a heterodimer of unique glycoprotein hormone subunit alpha (GPA)2 and glycoprotein hormone subunit beta (GPB)5 subunits with high affinity for the TSH receptor. Transgenic overexpression of GPB5 in mice results in cranial abnormalities, but the role of thyrostimulin in bone remains unknown. We hypothesized that thyrostimulin exerts paracrine actions in bone and determined: 1) GPA2 and GPB5 expression in osteoblasts and osteoclasts, 2) the skeletal consequences of thyrostimulin deficiency in GPB5 knockout (KO) mice, and 3) osteoblast and osteoclast responses to thyrostimulin treatment. Gpa2 and Gpb5 expression was identified in the newborn skeleton but declined rapidly thereafter. GPA2 and GPB5 mRNAs were also expressed in primary osteoblasts and osteoclasts at varying concentrations. Juvenile thyrostimulin-deficient mice had increased bone volume and mineralization as a result of increased osteoblastic bone formation. However, thyrostimulin failed to induce a canonical cAMP response or activate the noncanonical Akt, ERK, or mitogen-activated protein kinase (P38) signaling pathways in primary calvarial or bone marrow stromal cell-derived osteoblasts. Furthermore, thyrostimulin did not directly inhibit osteoblast proliferation, differentiation or mineralization in vitro. These studies identify thyrostimulin as a negative but indirect regulator of osteoblastic bone formation during skeletal development.

Show MeSH
Related in: MedlinePlus