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Updated: Jun 9, 2026
Skeletal Phenotype Analysis of a Conditional Stat3 Deletion Mouse Model
Published on: July 3, 2020
Double disruption of α2A- and α2C-adrenoceptors results in sympathetic hyperactivity and high-bone-mass phenotype
Tatiana L Fonseca1, Vanda Jorgetti, Cristiane C Costa
1Department of Anatomy, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil.
Abstract:
Evidence demonstrates that sympathetic nervous system (SNS) activation causes osteopenia via β(2)-adrenoceptor (β2-AR) signaling. Here we show that female mice with chronic sympathetic hyperactivity owing to double knockout of adrenoceptors that negatively regulate norepinephrine release, α(2A)-AR and α(2C)-AR (α(2A) /α(2C)-ARKO), present an unexpected and generalized phenotype of high bone mass with decreased bone resorption and increased formation. In α(2A) /α(2C)-ARKO versus wild-type (WT) mice, micro-computed tomographic (µCT) analysis showed increased, better connected, and more plate-shaped trabeculae in the femur and vertebra and increased cortical thickness in the vertebra, whereas biomechanical analysis showed increased tibial and femoral strength. Tibial mRNA expression of tartrate-resistant acid phosphatase (TRACP) and receptor activator of NF-κB (RANK), which are osteoclast-related factors, was lower in knockout (KO) mice. Plasma leptin and brain mRNA levels of cocaine amphetamine-regulated transcript (CART), which are factors that centrally affect bone turnover, and serum levels of estradiol were similar between mice strains. Tibial β(2)-AR mRNA expression also was similar in KO and WT littermates, whereas α(2A)-, α(2B)- and α(2C)-AR mRNAs were detected in the tibia of WT mice and in osteoblast-like MC3T3-E1 cells. By immunohistochemistry, we detected α(2A)-, α(2B)-, α(2C)- and β(2)-ARs in osteoblasts, osteoclasts, and chondrocytes of 18.5-day-old mouse fetuses and 35-day-old mice. Finally, we showed that isolated osteoclasts in culture are responsive to the selective α(2)-AR agonist clonidine and to the nonspecific α-AR antagonist phentolamine. These findings suggest that β(2)-AR is not the single adrenoceptor involved in bone turnover regulation and show that α(2)-AR signaling also may mediate the SNS actions in the skeleton.
Insights
Sympathetic nervous system (SNS) hyperactivity, caused by knocking out negative regulators of norepinephrine release (alpha-2A/2C-adrenoceptor knockout mice), unexpectedly increases bone mass. This suggests alpha-2-adrenoceptors play a role in SNS regulation of bone.
Area of Science:
- Skeletal Biology
- Neuroendocrinology
- Pharmacology
Background:
- Sympathetic nervous system (SNS) activation is known to cause osteopenia through beta(2)-adrenoceptor (β2-AR) signaling.
- The specific role of other adrenoceptors in regulating bone turnover remains less understood.
Purpose of the Study:
- To investigate the skeletal effects of chronic sympathetic hyperactivity resulting from the absence of negative adrenergic feedback.
- To determine the involvement of alpha-2 adrenoceptors (α(2)-ARs) in sympathetic regulation of bone mass.
Main Methods:
- Generation and analysis of female α(2A)/α(2C)-adrenoceptor knockout (α(2A)/α(2C)-ARKO) mice exhibiting chronic sympathetic hyperactivity.
- Micro-computed tomography (µCT) and biomechanical testing to assess bone structure and strength.
- Quantitative real-time PCR (qPCR) and immunohistochemistry to analyze adrenoceptor expression and bone-related factors in bone tissue and cells.
- In vitro studies on isolated osteoclasts to assess their response to adrenoceptor agonists and antagonists.
Main Results:
- α(2A)/α(2C)-ARKO mice displayed a high bone mass phenotype with significantly increased trabecular bone volume, connectivity, and cortical thickness compared to wild-type (WT) mice.
- Bone resorption markers (TRACP, RANK) were reduced in KO mice, while bone formation appeared increased.
- Expression of α(2A)-, α(2B)-, and α(2C)-ARs was detected in bone cells (osteoblasts, osteoclasts, chondrocytes), and isolated osteoclasts responded to α(2)-AR modulation.
- β(2)-AR mRNA levels were similar between KO and WT mice, indicating other adrenoceptors contribute to SNS effects on bone.
Conclusions:
- Chronic sympathetic hyperactivity, mediated by the absence of α(2)-AR negative feedback, leads to increased bone mass, challenging the sole role of β(2)-AR signaling.
- α(2)-ARs are expressed in bone cells and can modulate osteoclast activity, suggesting they are key mediators of sympathetic nervous system actions on the skeleton.
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