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Interleukin-6 expression and histomorphometry of bones from mice deficient in receptors for interleukin-1 or tumor
S J Vargas1, A Naprta, M Glaccum
1Department of Veterans Affairs Medical Center, Newington, Connecticut, USA.
Abstract:
We examined the roles of interleukin-1 Type I receptor (IL-1R1) and tumor necrosis factor receptor 1 (TNFR1) in bone metabolism using mice rendered deficient in these receptors by gene targeting. Sections of decalcified paraffin-embedded calvariae and humeri from 11- to 12-week-old mice deficient in IL-1 Type I receptor (IL-1R1-/-) or TNF receptor 1 (TNFR1-/-) were examined by histomorphometry. Wild-type mice (C57BL/6J x 129/J, WILD) served as controls. Interleukin-6 (IL-6) production in primary osteoblastic and bone marrow stromal cell cultures in response to parathyroid hormone (PTH, 100 ng/ml), IL-1 alpha (10 ng/ml), and TNF-alpha (10 ng/ml) was also examined. IL-1R1-/- and TNFR1-/- mice were viable and appeared phenotypically normal. However, the body weights of the IL-1R1-/- mice were 30% less than WILD, while the TNFR1-/- mice weighed 30% more than WILD mice of equivalent age. Calvariae and humeri of IL-1R1-/- and TNFR1-/- mice were normal with respect to trabecular bone volume, osteoclast number, osteoclast surface, growth plate widths, and cortical thickness. Receptor deficiency was confirmed by determining the ability of PTH, IL-1 alpha, and TNF-alpha to stimulate IL-6 in the media of primary calvaria-derived osteoblastic cell cultures from CD-1 and cytokine receptor-deficient mice. After 24 h of treatment, IL-1 alpha and TNF-alpha did not stimulate IL-6 production in osteoblasts from IL-1R1-/- and TNFR1-/- mice, respectively. In contrast, PTH increased IL-6 levels in the cells from all mice. IL-6 protein levels in bone marrow supernatants and conditioned media from untreated bone marrow stromal cells were undetectable in WILD, IL-1R1-/-, and TNFR1-/- mice. PTH, IL-1 alpha and TNF-alpha increased IL-6 mRNA and protein production in the WILD bone marrow stromal cells. In contrast, PTH and TNF-alpha increased IL-6 mRNA and protein levels in IL-1R1-/- bone marrow stromal cells while IL-1 alpha had no effect. These findings demonstrate that normal bone development in mice can occur in the absence of IL-1R1 or TNFR1 expression.
Insights
Mice lacking interleukin-1 Type I receptor (IL-1R1) or tumor necrosis factor receptor 1 (TNFR1) show normal bone development. These receptors are not essential for bone metabolism, despite influencing body weight and IL-6 production.
Area of Science:
- Immunology
- Endocrinology
- Bone Biology
Background:
- Interleukin-1 Type I receptor (IL-1R1) and tumor necrosis factor receptor 1 (TNFR1) are key mediators of inflammatory and immune responses.
- Their roles in normal bone metabolism and development are not fully elucidated.
Purpose of the Study:
- To investigate the necessity of IL-1R1 and TNFR1 for normal bone development and metabolism.
- To analyze the impact of these receptor deficiencies on bone structure and interleukin-6 (IL-6) production.
Main Methods:
- Gene targeting was used to create IL-1R1-/- and TNFR1-/- mice.
- Histomorphometry was performed on calvariae and humeri of deficient and wild-type mice.
- Interleukin-6 (IL-6) production was measured in osteoblastic and bone marrow stromal cell cultures stimulated with parathyroid hormone (PTH), IL-1 alpha, and TNF-alpha.
Main Results:
- IL-1R1-/- and TNFR1-/- mice were viable with normal bone structure (trabecular bone volume, osteoclast number, growth plate, cortical thickness).
- IL-1R1-/- mice had lower body weight, while TNFR1-/- mice had higher body weight compared to wild-type.
- Receptor deficiency affected IL-6 production in response to cytokines, but PTH-induced IL-6 production remained intact in osteoblasts; stromal cells showed altered responses to TNF-alpha and IL-1 alpha.
Conclusions:
- Normal bone development in mice can occur independently of IL-1R1 and TNFR1 expression.
- These receptors play a role in modulating IL-6 production in response to specific stimuli, but are not essential for overall bone formation.