Browsing by Author "Farach-Carson, Mary C."

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    Deletion of the auxiliary α2δ1 voltage sensitive calcium channel subunit in osteocytes and late-stage osteoblasts impairs femur strength and load-induced bone formation in male mice
    (Oxford, 2024) Wright, Christian S.; Lewis, Karl J.; Semon, Katelyn; Yi, Xin; Reyes Fernandez, Perla C.; Rust, Katie; Prideaux, Matthew; Schneider, Artur; Pederson, Molly; Deosthale, Padmini; Plotkin, Lilian I.; Hum, Julia M.; Sankar, Uma; Farach-Carson, Mary C.; Robling, Alexander G.; Thompson, William R.; Health Sciences, School of Health and Human Sciences
    Osteocytes sense and respond to mechanical force by controlling the activity of other bone cells. However, the mechanisms by which osteocytes sense mechanical input and transmit biological signals remain unclear. Voltage-sensitive calcium channels (VSCCs) regulate calcium (Ca2+) influx in response to external stimuli. Inhibition or deletion of VSCCs impairs osteogenesis and skeletal responses to mechanical loading. VSCC activity is influenced by its auxiliary subunits, which bind the channel’s α1 pore-forming subunit to alter intracellular Ca2+ concentrations. The α2δ1 auxiliary subunit associates with the pore-forming subunit via a glycosylphosphatidylinositol anchor and regulates the channel’s calcium-gating kinetics. Knockdown of α2δ1 in osteocytes impairs responses to membrane stretch, and global deletion of α2δ1 in mice results in osteopenia and impaired skeletal responses to loading in vivo. Therefore, we hypothesized that the α2δ1 subunit functions as a mechanotransducer, and its deletion in osteocytes would impair skeletal development and load-induced bone formation. Mice (C57BL/6) with LoxP sequences flanking Cacna2d1, the gene encoding α2δ1, were crossed with mice expressing Cre under the control of the Dmp1 promoter (10 kb). Deletion of α2δ1 in osteocytes and late-stage osteoblasts decreased femoral bone quantity (P < .05) by DXA, reduced relative osteoid surface (P < .05), and altered osteoblast and osteocyte regulatory gene expression (P < .01). Cacna2d1f/f, Cre + male mice displayed decreased femoral strength and lower 10-wk cancellous bone in vivo micro-computed tomography measurements at the proximal tibia (P < .01) compared to controls, whereas Cacna2d1f/f, Cre + female mice showed impaired 20-wk cancellous and cortical bone ex vivo micro-computed tomography measurements (P < .05) vs controls. Deletion of α2δ1 in osteocytes and late-stage osteoblasts suppressed load-induced calcium signaling in vivo and decreased anabolic responses to mechanical loading in male mice, demonstrating decreased mechanosensitivity. Collectively, the α2δ1 auxiliary subunit is essential for the regulation of osteoid-formation, femur strength, and load-induced bone formation in male mice.
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    Effects of Gabapentin and Pregabalin on Calcium Homeostasis: Implications for Physical Rehabilitation of Musculoskeletal Tissues
    (Springer, 2022) Reyes Fernandez, Perla C.; Wright, Christian S.; Warden, Stuart J.; Hum, Julia; Farach-Carson, Mary C.; Thompson, William R.; Physical Therapy, School of Health and Human Sciences
    Purpose of review: In this review, we discuss the mechanism of action of gabapentinoids and the potential consequences of long-term treatment with these drugs on the musculoskeletal system. Recent findings: Gabapentinoids, such as gabapentin (GBP) and pregabalin (PGB) were designed as antiepileptic reagents and are now commonly used as first-line treatment for neuropathic pain and increasingly prescribed off-label for other pain disorders such as migraines and back pain. GBP and PGB exert their analgesic actions by selectively binding the α2δ1 auxiliary subunit of voltage-sensitive calcium channels, thereby inhibiting channel function. Numerous tissues express the α2δ1 subunit where GBP and PGB can alter calcium-mediated signaling events. In tissues such as bone, muscle, and cartilage, α2δ1 has important roles in skeletal formation, mechanosensation, and normal tissue function/repair that may be affected by chronic use of gabapentinoids. Long-term use of gabapentinoids is associated with detrimental musculoskeletal outcomes, including increased fracture risk. Therefore, understanding potential complications is essential for clinicians to guide appropriate treatments.
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    Examining Mechanisms for Voltage-Sensitive Calcium Channel-Mediated Secretion Events in Bone Cells
    (Springer, 2023) Reyes Fernandez, Perla C.; Wright, Christian S.; Farach-Carson, Mary C.; Thompson, William R.; Physical Therapy, School of Health and Human Sciences
    In addition to their well-described functions in cell excitability, voltage-sensitive calcium channels (VSCCs) serve a critical role in calcium (Ca2+)-mediated secretion of pleiotropic paracrine and endocrine factors, including those produced in bone. Influx of Ca2+ through VSCCs activates intracellular signaling pathways to modulate a variety of cellular processes that include cell proliferation, differentiation, and bone adaptation in response to mechanical stimuli. Less well understood is the role of VSCCs in the control of bone and calcium homeostasis mediated through secreted factors. In this review, we discuss the various functions of VSCCs in skeletal cells as regulators of Ca2+ dynamics and detail how these channels might control the release of bioactive factors from bone cells. Because VSCCs are druggable, a better understanding of the multiple functions of these channels in the skeleton offers the opportunity for developing new therapies to enhance and maintain bone and to improve systemic health.
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    Gabapentin Disrupts Binding of Perlecan to the α2δ1 Voltage Sensitive Calcium Channel Subunit and Impairs Skeletal Mechanosensation
    (MDPI, 2022-12-12) Reyes Fernandez, Perla C.; Wright, Christian S.; Masterson, Adrianna N.; Yi, Xin; Tellman, Tristen V.; Bonteanu, Andrei; Rust, Katie; Noonan, Megan L.; White, Kenneth E.; Lewis, Karl J.; Sankar, Uma; Hum, Julia M.; Bix, Gregory; Wu, Danielle; Robling, Alexander G.; Sardar, Rajesh; Farach-Carson, Mary C.; Thompson, William R.; Physical Therapy, School of Health and Human Sciences
    Our understanding of how osteocytes, the principal mechanosensors within bone, sense and perceive force remains unclear. Previous work identified "tethering elements" (TEs) spanning the pericellular space of osteocytes and transmitting mechanical information into biochemical signals. While we identified the heparan sulfate proteoglycan perlecan (PLN) as a component of these TEs, PLN must attach to the cell surface to induce biochemical responses. As voltage-sensitive calcium channels (VSCCs) are critical for bone mechanotransduction, we hypothesized that PLN binds the extracellular α2δ1 subunit of VSCCs to couple the bone matrix to the osteocyte membrane. Here, we showed co-localization of PLN and α2δ1 along osteocyte dendritic processes. Additionally, we quantified the molecular interactions between α2δ1 and PLN domains and demonstrated for the first time that α2δ1 strongly associates with PLN via its domain III. Furthermore, α2δ1 is the binding site for the commonly used pain drug, gabapentin (GBP), which is associated with adverse skeletal effects when used chronically. We found that GBP disrupts PLN::α2δ1 binding in vitro, and GBP treatment in vivo results in impaired bone mechanosensation. Our work identified a novel mechanosensory complex within osteocytes composed of PLN and α2δ1, necessary for bone force transmission and sensitive to the drug GBP.
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    Loss of the auxiliary α2δ1 voltage-sensitive calcium channel subunit impairs bone formation and anabolic responses to mechanical loading
    (Oxford University Press, 2024-01-10) Kelly, Madison M.; Sharma, Karan; Wright, Christian S.; Yi, Xin; Reyes Fernandez, Perla C.; Gegg, Aaron T.; Gorrell, Taylor A.; Noonan, Megan L.; Baghdady, Ahmed; Sieger, Jacob A.; Dolphin, Annette C.; Warden, Stuart J.; Deosthale, Padmini; Plotkin, Lilian I.; Sankar, Uma; Hum, Julia M.; Robling, Alexander G.; Farach-Carson, Mary C.; Thompson, William R.; Physical Therapy, School of Health and Human Sciences
    Voltage-sensitive calcium channels (VSCCs) influence bone structure and function, including anabolic responses to mechanical loading. While the pore-forming (α1) subunit of VSCCs allows Ca2+ influx, auxiliary subunits regulate the biophysical properties of the pore. The α2δ1 subunit influences gating kinetics of the α1 pore and enables mechanically induced signaling in osteocytes; however, the skeletal function of α2δ1 in vivo remains unknown. In this work, we examined the skeletal consequences of deleting Cacna2d1, the gene encoding α2δ1. Dual-energy X-ray absorptiometry and microcomputed tomography imaging demonstrated that deletion of α2δ1 diminished bone mineral content and density in both male and female C57BL/6 mice. Structural differences manifested in both trabecular and cortical bone for males, while the absence of α2δ1 affected only cortical bone in female mice. Deletion of α2δ1 impaired skeletal mechanical properties in both sexes, as measured by three-point bending to failure. While no changes in osteoblast number or activity were found for either sex, male mice displayed a significant increase in osteoclast number, accompanied by increased eroded bone surface and upregulation of genes that regulate osteoclast differentiation. Deletion of α2δ1 also rendered the skeleton insensitive to exogenous mechanical loading in males. While previous work demonstrates that VSCCs are essential for anabolic responses to mechanical loading, the mechanism by which these channels sense and respond to force remained unclear. Our data demonstrate that the α2δ1 auxiliary VSCC subunit functions to maintain baseline bone mass and strength through regulation of osteoclast activity and also provides skeletal mechanotransduction in male mice. These data reveal a molecular player in our understanding of the mechanisms by which VSCCs influence skeletal adaptation.
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    Loss of the auxiliary α2δ1 voltage-sensitive calcium channel subunit impairs bone formation and anabolic responses to mechanical loading
    (Oxford, 2024-01) Kelly, Madison M.; Sharma, Karan; Wright, Christian S.; Yi, Xin; Reyes Fernandez, Perla C.; Gegg, Aaron T.; Gorrell, Taylor A.; Noonan, Megan L.; Baghdady, Ahmed; Sieger, Jacob A.; Dolphin, Annette C.; Warden, Stuart J.; Deosthale, Padmini; Plotkin, Lilian I.; Sankar, Uma; Hum, Julia M.; Robling, Alexander G.; Farach-Carson, Mary C.; Thompson, William R.; Health Sciences, School of Health and Human Sciences
    Voltage-sensitive calcium channels (VSCCs) influence bone structure and function, including anabolic responses to mechanical loading. While the pore-forming (α1) subunit of VSCCs allows Ca2+ influx, auxiliary subunits regulate the biophysical properties of the pore. The α2δ1 subunit influences gating kinetics of the α1 pore and enables mechanically induced signaling in osteocytes; however, the skeletal function of α2δ1 in vivo remains unknown. In this work, we examined the skeletal consequences of deleting Cacna2d1, the gene encoding α2δ1. Dual-energy X-ray absorptiometry and microcomputed tomography imaging demonstrated that deletion of α2δ1 diminished bone mineral content and density in both male and female C57BL/6 mice. Structural differences manifested in both trabecular and cortical bone for males, while the absence of α2δ1 affected only cortical bone in female mice. Deletion of α2δ1 impaired skeletal mechanical properties in both sexes, as measured by three-point bending to failure. While no changes in osteoblast number or activity were found for either sex, male mice displayed a significant increase in osteoclast number, accompanied by increased eroded bone surface and upregulation of genes that regulate osteoclast differentiation. Deletion of α2δ1 also rendered the skeleton insensitive to exogenous mechanical loading in males. While previous work demonstrates that VSCCs are essential for anabolic responses to mechanical loading, the mechanism by which these channels sense and respond to force remained unclear. Our data demonstrate that the α2δ1 auxiliary VSCC subunit functions to maintain baseline bone mass and strength through regulation of osteoclast activity and also provides skeletal mechanotransduction in male mice. These data reveal a molecular player in our understanding of the mechanisms by which VSCCs influence skeletal adaptation.
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    Skeletal Functions of Voltage Sensitive Calcium Channels
    (Springer, 2021) Wright, Christian S.; Robling, Alexander G.; Farach-Carson, Mary C.; Thompson, William R.; Physical Therapy, School of Health and Human Sciences
    Voltage-sensitive calcium channels (VSCCs) are ubiquitous multimeric protein complexes that are necessary for the regulation of numerous physiological processes. VSCCs regulate calcium influx and various intracellular processes including muscle contraction, neurotransmission, hormone secretion, and gene transcription, with function specificity defined by the channel‟s subunits and tissue location. The functions of VSCCs in bone are often overlooked since bone is not considered an electrically excitable tissue. However, skeletal homeostasis and adaptation relies heavily on VSCCs. Inhibition or deletion of VSCCs decreases osteogenesis, impairs skeletal structure, and impedes anabolic responses to mechanical loading. While the functions of VSCCs in osteoclasts is less clear, VSCCs have distinct but complementary functions in osteoblasts and osteocytes. This review details the structure, function, and nomenclature of VSCCs, followed by a comprehensive description of the known functions of VSCCs in bone cells and their regulation of bone development, bone formation, and mechanotransduction.