Browsing by Author "Klunk, Angela"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Conditional Loss of Nmp4 in Mesenchymal Stem Progenitor Cells Enhances PTH-Induced Bone Formation
    (Oxford University Press, 2023) Atkinson, Emily G.; Adaway, Michele; Horan, Daniel J.; Korff, Crystal; Klunk, Angela; Orr, Ashley L.; Ratz, Katherine; Bellido, Teresita; Plotkin, Lilian I.; Robling, Alexander G.; Bidwell, Joseph P.; Anatomy, Cell Biology and Physiology, School of Medicine
    Activation of bone anabolic pathways is a fruitful approach for treating severe osteoporosis. Yet, FDA-approved osteoanabolics, e.g., parathyroid hormone (PTH), have limited efficacy. Improving their potency is a promising strategy for maximizing bone anabolic output. Nmp4 (Nuclear Matrix Protein 4) global knockout mice, exhibit enhanced PTH-induced increases in trabecular bone but display no overt baseline skeletal phenotype. Nmp4 is expressed in all tissues; therefore, to determine which cell type is responsible for driving the beneficial effects of Nmp4 inhibition, we conditionally removed this gene from cells at distinct stages of osteogenic differentiation. Nmp4-floxed (Nmp4fl/fl) mice were crossed with mice bearing one of three Cre drivers including (i) Prx1Cre+ to remove Nmp4 from mesenchymal stem/progenitor cells (MSPCs) in long bones; (ii) BglapCre+ targeting mature osteoblasts and (iii) Dmp1Cre+ to disable Nmp4 in osteocytes. Virgin female Cre+ and Cre− mice (10wks of age) were sorted into cohorts by weight and genotype. Mice were administered daily injections of either human PTH 1–34 at 30μg/kg, or vehicle for 4wks or 7wks. Skeletal response was assessed using dual-energy X-ray absorptiometry, microcomputed tomography, bone histomorphometry and serum analysis for remodeling markers. Nmp4fl/fl;Prx1Cre+ mice virtually phenocopied the global Nmp4−/− skeleton in the femur, i.e., a mild baseline phenotype but significantly enhanced PTH-induced increase in femur trabecular bone volume/total volume (BV/TV) compared to their Nmp4fl/fl;Prx1Cre− controls. This was not observed in the spine, where Prrx1 is not expressed. Heightened response to PTH was coincident with enhanced bone formation. Conditional loss of Nmp4 from the mature osteoblasts (Nmp4fl/fl;BglapCre+) failed to increase BV/TV or enhance PTH response. However, conditional disabling of Nmp4 in osteocytes (Nmp4fl/fl;Dmp1Cre+) increased BV/TV without boosting response to hormone under our experimental regimen. We conclude that Nmp4−/− Prx1-expressing MSPCs drive the improved response to PTH therapy, and that this gene has stage-specific effects on osteoanabolism.
  • Thumbnail Image
    Item
    Loss of Nmp4 optimizes osteogenic metabolism and secretion to enhance bone quality
    (APS, 2019) Shao, Yu; Wichern, Emily; Childress, Paul J.; Adaway, Michele; Misra, Jagannath; Klunk, Angela; Burr, David B.; Wek, Ronald C.; Mosley, Amber L.; Liu, Yunlong; Robling, Alexander G.; Brustovetsky, Nickolay; Hamilton, James; Jacobs, Kylie; Vashishth, Deepak; Stayrook, Keith R.; Allen, Matthew R.; Wallace, Joseph M.; Bidwell, Joseph P.; Anatomy and Cell Biology, IU School of Medicine
    A goal of osteoporosis therapy is to restore lost bone with structurally sound tissue. Mice lacking the transcription factor Nuclear Matrix Protein 4 (Nmp4, Zfp384, Ciz, ZNF384) respond to several classes of osteoporosis drugs with enhanced bone formation compared to wild type (WT) animals. Nmp4-/- mesenchymal stem/progenitor cells (MSPCs) exhibit an accelerated and enhanced mineralization during osteoblast differentiation. To address the mechanisms underlying this hyper-anabolic phenotype, we carried out RNA-sequencing and molecular and cellular analyses of WT and Nmp4-/- MSPCs during osteogenesis to define pathways and mechanisms associated with elevated matrix production. We determined that Nmp4 has a broad impact on the transcriptome during osteogenic differentiation, contributing to the expression of over 5,000 genes. Phenotypic anchoring of transcriptional data was performed for the hypothesis-testing arm through analysis of cell metabolism, protein synthesis and secretion, and bone material properties. Mechanistic studies confirmed that Nmp4-/- MSPCs exhibited an enhanced capacity for glycolytic conversion- a key step in bone anabolism. Nmp4-/- cells showed elevated collagen translation and secretion. Expression of matrix genes that contribute to bone material-level mechanical properties were elevated in Nmp4-/- cells, an observation that was supported by biomechanical testing of bone samples from Nmp4-/- and WT mice. We conclude that loss of Nmp4 increases the magnitude of glycolysis upon the metabolic switch, which fuels the conversion of the osteoblast into a super-secretor of matrix resulting in more bone with improvements in intrinsic quality.
  • Thumbnail Image
    Item
    Nmp4, a Regulator of Induced Osteoanabolism, Also Influences Insulin Secretion and Sensitivity
    (Springer, 2022) Bidwell, Joseph; Tersey, Sarah A.; Adaway, Michele; Bone, Robert N.; Creecy, Amy; Klunk, Angela; Atkinson, Emily G.; Wek, Ronald C.; Robling, Alexander G.; Wallace, Joseph M.; Evans-Molina, Carmella; Anatomy, Cell Biology and Physiology, School of Medicine
    A bidirectional and complex relationship exists between bone and glycemia. Persons with type 2 diabetes (T2D) are at risk for bone loss and fracture, however, heightened osteoanabolism may ameliorate T2D-induced deficits in glycemia as bone-forming osteoblasts contribute to energy metabolism via increased glucose uptake and cellular glycolysis. Mice globally lacking Nuclear Matrix Protein 4 (Nmp4), a transcription factor expressed in all tissues and conserved between humans and rodents, are healthy and exhibit enhanced bone formation in response to anabolic osteoporosis therapies. To test whether loss of Nmp4 similarly impacted bone deficits caused by diet induced obesity, male wild type (WT) and Nmp4−/− mice (8wks) were fed either low-fat diet (LFD) or high-fat diet (HFD) for 12wks. Endpoint parameters included bone architecture, structural and estimated tissue level mechanical properties, body weight/composition, glucose-stimulated insulin secretion, glucose tolerance, insulin tolerance and metabolic cage analysis. HFD diminished bone architecture and ultimate force and stiffness equally in both genotypes. Unexpectedly, the Nmp4−/− mice exhibited deficits in pancreatic β-cell function and were modestly glucose intolerant under normal diet conditions. Despite the β-cell deficits, the Nmp4−/− mice were less sensitive to HFD-induced weight gain, increases in % fat mass, and decreases in glucose tolerance and insulin sensitivity. We conclude that Nmp4 supports pancreatic β-cell function but suppresses peripheral glucose utilization, perhaps contributing to its suppression of induced skeletal anabolism. Selective disruption of Nmp4 in peripheral tissues may provide a strategy for improving both induced osteoanabolism and energy metabolism in comorbid patients.
  • Thumbnail Image
    Item
    NMP4, An Arbiter of Bone Cell Secretory Capacity And Regulator of Skeletal Response to PTH Therapy
    (Springer, 2023) Korff, Crystal; Atkinson, Emily; Adaway, Michele; Klunk, Angela; Wek, Ronald C.; Vashishth, Deepak; Wallace, Joseph M.; Anderson-Baucum, Emily K.; Evans-Molina, Carmella; Robling, Alexander G.; Bidwell, Joseph P.; Medical and Molecular Genetics, School of Medicine
    The skeleton is a secretory organ, and the goal of some osteoporosis therapies is to maximize bone matrix output. Nmp4 encodes a novel transcription factor that regulates bone cell secretion as part of its functional repertoire. Loss of Nmp4 enhances bone response to osteoanabolic therapy, in part, by increasing the production and delivery of bone matrix. Nmp4 shares traits with scaling factors, which are transcription factors that influence the expression of hundreds of genes to govern proteome allocation for establishing secretory cell infrastructure and capacity. Nmp4 is expressed in all tissues and while global loss of this gene leads to no overt baseline phenotype, deletion of Nmp4 has broad tissue effects in mice challenged with certain stressors. In addition to an enhanced response to osteoporosis therapies, Nmp4-deficient mice are less sensitive to high fat diet-induced weight gain and insulin resistance, exhibit a reduced disease severity in response to influenza A virus (IAV) infection, and resist the development of some forms of rheumatoid arthritis. In this review, we present the current understanding of the mechanisms underlying Nmp4 regulation of the skeletal response to osteoanabolics, and we discuss how this unique gene contributes to the diverse phenotypes among different tissues and stresses. An emerging theme is that Nmp4 is important for the infrastructure and capacity of secretory cells that are critical for health and disease.