Propranolol Promotes Bone Formation and Limits Resorption Through Novel Mechanisms During Anabolic Parathyroid Hormone Treatment in Female C57BL/6J Mice

Targeting the central and peripheral nervous system to regulate bone homeostasis: mechanisms and potential therapies

The skeleton is innervated by different types of nerves and receives signaling from the nervous system to maintain homeostasis and facilitate regeneration or repair. Although the role of peripheral nerves and signals in regulating bone homeostasis has been extensively investigated, the intimate relationship between the central nervous system and bone remains less understood, yet it has emerged as a hot topic in the bone field. In this review, we discussed clinical observations and animal studies that elucidate the connection between the nervous system and bone metabolism, either intact or after injury. First, we explored mechanistic studies linking specific brain nuclei with bone homeostasis, including the ventromedial hypothalamus, arcuate nucleus, paraventricular hypothalamic nucleus, amygdala, and locus coeruleus. We then focused on the characteristics of bone innervation and nerve subtypes, such as sensory, sympathetic, and parasympathetic nerves. Moreover, we summarized the molecular features and regulatory functions of these nerves. Finally, we included available translational approaches that utilize nerve function to improve bone homeostasis and promote bone regeneration. Therefore, considering the nervous system within the context of neuromusculoskeletal interactions can deepen our understanding of skeletal homeostasis and repair process, ultimately benefiting future clinical translation.

Pharmacogenetic and microRNA mechanisms of beta blocker use on bone

Motivated by studies showing an association between beta blocker (BB) use and positive bone outcomes, a pilot randomized control trial was performed at the Mayo Clinic which randomized postmenopausal women to placebo, propranolol (40 or 80 mg twice daily), atenolol (50 mg/d), or nebivolol (5 mg/d) to determine changes in bone turnover markers (BTMs) and in BMD over 20 wk. Pharmacogenetic effects and microRNA-mediated mechanisms involving beta adrenergic receptor and related genes have previously been found. We sought to validate these effects and discover new candidates in an ancillary study to the pilot clinical trial. We genotyped all participants and performed microRNA (miRNA) sequencing at baseline and at 20 wk for 24 participants from the atenolol or placebo groups. We discovered several variants in ADRB1, ADRB2, and HDAC4 which showed significant pharmacogenetic effects with BMD at multiple sites and with BTMs. Our miRNA results showed a significant treatment effect for miR-19a-3p over time with atenolol use in the low-responder group compared to placebo. Overall, the longitudinal miRNA analysis showed a large number of miRNAs which were up-regulated over the trial in the low responders but not the high responders compared to placebo, of which miR-19a-3p was one example. Finally, we compared the response to atenolol treatment for cardiovascular traits (pulse and blood pressure) with the response for the bone resorption marker, C-terminal telopeptide, and found a largely independent effect. Our results have implications for personalized therapy and for understanding mechanisms of BB treatment effect on bone.

Unraveling the Mechanism of Impaired Osteogenic Differentiation in Osteoporosis: Insights from ADRB2 Gene Polymorphism

Osteoporosis is characterized by increased resorption and decreased bone formation; it is predominantly influenced by genetic factors. G-protein coupled receptors (GPCRs) play a vital role in bone homeostasis, and mutations in these genes are associated with osteoporosis. This study aimed to investigate the impact of single nucleotide polymorphism (SNP) rs1042713 in the ADRB2 gene, encoding the beta-2-adrenergic receptor, on osteoblastogenesis. Herein, using quantitative polymerase chain reaction, western immunoblotting, immunofluorescence assays, and flow cytometry, we examined the expression of ADRB2 and markers of bone matrix synthesis in mesenchymal stem cells (MSCs) derived from osteoporosis patient (OP-MSCs) carrying ADRB2 SNP in comparison with MSCs from healthy donor (HD-MSCs). The results showed significantly reduced ADRB2 expression in OP-MSCs at both the mRNA and protein levels, alongside decreased type 1 collagen expression, a key bone matrix component. Notably, OP-MSCs exhibited increased ERK kinase expression during differentiation, indicating sustained cell cycle progression, unlike that going to HD-MSC. These results provide novel insights into the association of ADRB2 gene polymorphisms with osteogenic differentiation. The preserved proliferative activity of OP-MSCs with rs1042713 in ADRB2 contributes to their inability to undergo effective osteogenic differentiation. This research suggests that targeting genetic factors may offer new therapeutic strategies to mitigate osteoporosis progression.

Protective Effects of β-Blockers on Bone in Older Adults with Dementia

Increased β-adrenergic receptor activity has been hypothesized to cause bone loss in those with dementia. We investigated the effect of long-term β-blocker use on rate of bone loss in older adults with dementia. We used a linear mixed-effects model to estimate the relationship between long-term β-blocker use and rate of bone loss in participants from the Health Aging and Body Composition study. Records of 1198 participants were analyzed, 44.7% were men. Among the men, 25.2% had dementia and 20.2% were on β-blockers, while in the women, 22.5% had dementia and 16.6% received β-blockers. In the 135 men with dementia, 23 were taking β-blockers, while 15 of 149 women with dementia were using β-blockers. In men with dementia, β-blocker users had 0.00491 g/cm2 less bone mineral density (BMD) loss per year at the femoral neck (i.e., 0.63% less loss per year) than non-users (p < 0.05). No differences were detected in women with or without dementia and men without dementia. β-blockers may be protective by slowing down bone loss in older men with dementia.

Advanced Progress of the Relationship Between Antihypertensive Drugs and Bone Metabolism

Hypertension and osteoporosis are common comorbidities among elderly individuals. Drug therapy has been widely used in clinical practice as the preferred antihypertensive treatment. Therefore, antihypertensive drugs have become some of the most commonly prescribed drugs in healthcare settings. However, antihypertensive drugs have different effects on bone metabolism. The results of animal and clinical studies on the effects of antihypertensive drugs on osteoporosis or fracture risk are controversial and have aroused widespread concern among clinicians. Recent studies found that angiotensin receptor blockers, selective β-adrenergic receptor blockers, and thiazide diuretics might improve bone trabecular number and bone mineral density by stimulating osteoblast differentiation, reducing osteoclast generation, and other mechanism. Furthermore, nonselective β-adrenergic receptor blockers and dihydropyridine calcium channel blockers were found to have no significant relationship with bone mineral density or bone strength, and α-adrenergic receptor blockers and loop diuretics might increase fracture risk by decreasing bone mineral density. This article aimed to review previous animal experiments, clinical studies, and meta-analyses focusing on the effects of different antihypertensive drugs on bone metabolism, and to provide a new approach for the prevention and treatment of osteoporosis.

Role of the Peripheral Nervous System in Skeletal Development and Regeneration: Controversies and Clinical Implications

PURPOSE OF REVIEW

This review examines the diverse functional relationships that exist between the peripheral nervous system (PNS) and bone, including key advances over the past century that inform our efforts to translate these discoveries for skeletal repair.

RECENT FINDINGS

The innervation of the bone during development, homeostasis, and regeneration is highly patterned. Consistent with this, there have been nearly 100 studies over the past century that have used denervation approaches to isolate the effects of the different branches of the PNS on the bone. Overall, a common theme of balance emerges whereby an orchestration of both local and systemic neural functions must align to promote optimal skeletal repair while limiting negative consequences such as pain. An improved understanding of the functional bidirectional pathways linking the PNS and bone has important implications for skeletal development and regeneration. Clinical advances over the next century will necessitate a rigorous identification of the mechanisms underlying these effects that is cautious not to oversimplify the in vivo condition in diverse states of health and disease.

Sustained Morphine Delivery Suppresses Bone Formation and Alters Metabolic and Circulating miRNA Profiles in Male C57BL/6J Mice

Opioid use is detrimental to bone health, causing both indirect and direct effects on bone turnover. Although the mechanisms of these effects are not entirely clear, recent studies have linked chronic opioid use to alterations in circulating miRNAs. Here, we developed a model of opioid-induced bone loss to understand bone turnover and identify candidate miRNA-mediated regulatory mechanisms. We evaluated the effects of sustained morphine treatment on male and female C57BL/6J mice by treating with vehicle (0.9% saline) or morphine (17 mg/kg) using subcutaneous osmotic minipumps for 25 days. Morphine-treated mice had higher energy expenditure and respiratory quotient, indicating a shift toward carbohydrate metabolism. Micro-computed tomography (μCT) analysis indicated a sex difference in the bone outcome, where male mice treated with morphine had reduced trabecular bone volume fraction (Tb.BV/TV) (15%) and trabecular bone mineral density (BMD) (14%) in the distal femur compared with vehicle. Conversely, bone microarchitecture was not changed in females after morphine treatment. Histomorphometric analysis demonstrated that in males, morphine reduced bone formation rate compared with vehicle, but osteoclast parameters were not different. Furthermore, morphine reduced bone formation marker gene expression in the tibia of males (Bglap and Dmp1). Circulating miRNA profile changes were evident in males, with 14 differentially expressed miRNAs associated with morphine treatment compared with two differentially expressed miRNAs in females. In males, target analysis indicated hypoxia-inducible factor (HIF) signaling pathway was targeted by miR-223-3p and fatty acid metabolism by miR-484, -223-3p, and -328-3p. Consequently, expression of miR-223-3p targets, including Igf1r and Stat3, was lower in morphine-treated bone. In summary, we have established a model where morphine leads to a lower trabecular bone formation in males and identified potential mediating miRNAs. Understanding the sex-specific mechanisms of bone loss from opioids will be important for improving management of the adverse effects of opioids on the skeleton. © 2022 American Society for Bone and Mineral Research (ASBMR).

Sustainable Release of Propranolol Hydrochloride Laden with Biconjugated-Ufasomes Chitosan Hydrogel Attenuates Cisplatin-Induced Sciatic Nerve Damage in In Vitro/In Vivo Evaluation

Peripheral nerve injuries significantly impact patients' quality of life and poor functional recovery. Chitosan-ufasomes (CTS-UFAs) exhibit biomimetic features, making them a viable choice for developing novel transdermal delivery for neural repair. This study aimed to investigate the role of CTS-UFAs loaded with the propranolol HCl (PRO) as a model drug in enhancing sciatica in cisplatin-induced sciatic nerve damage in rats. Hence, PRO-UFAs were primed, embedding either span 20 or 60 together with oleic acid and cholesterol using a thin-film hydration process based on full factorial design (24). The influence of formulation factors on UFAs' physicochemical characteristics and the optimum formulation selection were investigated using Design-Expert® software. Based on the optimal UFA formulation, PRO-CTS-UFAs were constructed and characterized using transmission electron microscopy, stability studies, and ex vivo permeation. In vivo trials on rats with a sciatic nerve injury tested the efficacy of PRO-CTS-UFA and PRO-UFA transdermal hydrogels, PRO solution, compared to normal rats. Additionally, oxidative stress and specific apoptotic biomarkers were assessed, supported by a sciatic nerve histopathological study. PRO-UFAs and PRO-CTS-UFAs disclosed entrapment efficiency of 82.72 ± 2.33% and 85.32 ± 2.65%, a particle size of 317.22 ± 6.43 and 336.12 ± 4.9 nm, ζ potential of -62.06 ± 0.07 and 65.24 ± 0.10 mV, and accumulatively released 70.95 ± 8.14% and 64.03 ± 1.9% PRO within 6 h, respectively. Moreover, PRO-CTS-UFAs significantly restored sciatic nerve structure, inhibited the cisplatin-dependent increase in peripheral myelin 22 gene expression and MDA levels, and further re-established sciatic nerve GSH and CAT content. Furthermore, they elicited MBP re-expression, BCL-2 mild expression, and inhibited TNF-α expression. Briefly, our findings proposed that CTS-UFAs are promising to enhance PRO transdermal delivery to manage sciatic nerve damage.

Myeloid cell-derived catecholamines influence bone turnover and regeneration in mice

Catecholamine signaling is known to influence bone tissue as reuptake of norepinephrine released from sympathetic nerves into bone cells declines with age leading to osteoporosis. Further, β-adrenoceptor-blockers like propranolol provoke osteoprotective effects in osteoporotic patients. However, besides systemic adrenal and sympathetic catecholamine production, it is also known that myeloid cells can synthesize catecholamines, especially under inflammatory conditions. To investigate the effects of catecholamines produced by CD11b⁺ myeloid cells on bone turnover and regeneration, a mouse line with specific knockout of tyrosine hydroxylase, the rate-limiting enzyme of catecholamine synthesis, in CD11b⁺ myeloid cells (TH^flox/flox/CD11b-Cre⁺, referred to as TH^CD11b-Cre) was generated. For bone phenotyping, male mice were sacrificed at eight and twelve weeks of age and harvested bones were subjected to bone length measurement, micro-computed tomography, fluorescence-activated cell sorting of the bone marrow, gene expression analysis, histology and immunohistochemistry. Support for an age-dependent influence of myeloid cell-derived catecholamines on bone homeostasis is provided by the fact that twelve-week-old, but not eight-week-old TH^CD11b-Cre mice, developed an osteopenic phenotype and showed increased numbers of neutrophils and T lymphocytes in the bone marrow, while CCL2, IL-6, IL-4 and IL-10 mRNA expression was reduced in sorted myeloid bone marrow cells. To investigate the influence of myeloid cell-derived catecholamines on fracture healing, mice received a diaphyseal femur osteotomy. Three days post-fracture, immunohistochemistry revealed an increased number of macrophages, neutrophils and cytotoxic T lymphocytes in the fracture hematoma of TH^CD11b-Cre mice. Micro-computed tomography on day 21 showed a decreased tissue mineral density, a reduced bone volume and less trabeculae in the fracture callus indicating delayed fracture healing, probably due to the increased presence of inflammatory cells in TH^CD11b-Cre mice. This indicates a crucial role of myeloid cell-derived catecholamines in immune cell-bone cell crosstalk and during fracture healing.