Reporting guidelines, review of methodological standards, and challenges toward harmonization in bone marrow adiposity research. Report of the Methodologies Working Group of the International Bone Marrow Adiposity Society

The interest in bone marrow adiposity (BMA) has increased over the last decade due to its association with, and potential role, in a range of diseases (osteoporosis, diabetes, anorexia, cancer) as well as treatments (corticosteroid, radiation, chemotherapy, thiazolidinediones). However, to advance the field of BMA research, standardization of methods is desirable to increase comparability of study outcomes and foster collaboration. Therefore, at the 2017 annual BMA meeting, the International Bone Marrow Adiposity Society (BMAS) founded a working group to evaluate methodologies in BMA research. All BMAS members could volunteer to participate. The working group members, who are all active preclinical or clinical BMA researchers, searched the literature for articles investigating BMA and discussed the results during personal and telephone conferences. According to the consensus opinion, both based on the review of the literature and on expert opinion, we describe existing methodologies and discuss the challenges and future directions for (1) histomorphometry of bone marrow adipocytes, (2

MarrowQuant across aging and aplasia: A digital pathology workflow for quantification of bone marrow compartments in histological sections

The bone marrow (BM) exists heterogeneously as hematopoietic/red or adipocytic/yellow marrow depending on skeletal location, age, and physiological condition. Mouse models and patients undergoing radio/chemotherapy or suffering acute BM failure endure rapid adipocytic conversion of the marrow microenvironment, the so-called red-to-yellow transition. Following hematopoietic recovery, such as upon BM transplantation, a yellow-to-red transition occurs and functional hematopoiesis is restored. Gold Standards to estimate BM cellular composition are pathologists\u27 assessment of hematopoietic cellularity in hematoxylin and eosin (H&E) stained histological sections as well as volumetric measurements of marrow adiposity with contrast-enhanced micro-computerized tomography (CE-μCT) upon osmium-tetroxide lipid staining. Due to user-dependent variables, reproducibility in longitudinal studies is a challenge for both methods. Here we report the development of a semi-automated image analysis plug-in

Regulation of Bone Formation and Pathology by Local Actions of Leptin in the Bone Marrow.

Site-specific adipose content of the bone marrow has been noted since the inclusion of meat into the hominid diet, evidenced by marrow removal from ungulate limb bones, 2.6 million years ago. Association between marrow fat and bone metabolism has since been documented, however the mechanism for this relationship remains unknown. Leptin, a secreted adipocytokine, possesses the ability to regulate bone formation centrally through the hypothalamus and peripherally though marrow cells such as the osteoblast. Until the recent generation of a mouse with loxP sites flanking exon17 of the signaling-competent leptin receptor (ObRb), the physiologic contribution of peripheral leptin signaling to bone formation could not be determined. Leptin has been shown to increase mineralization of primary bone marrow stromal precursor cells (MPCs) and osteoblasts in vitro. Leptin is also a potent regulator of pro-inflammatory macrophage cytokine output. We therefore examined the ability of leptin to modulate bone formation through the myeloid lineage, the osteoblast, and the MPC by generating mice with conditional deletion of ObRb using LysozymeM 2 (LysM), Col2.3, and Col3.6 promoters driving Cre recombinase respectively. Myeloid-specific deletion of ObRb resulted in a mild, gender-specific bone phenotype in 52 week old animals with decreases in trabecular parameters noted in females and increases in cortical values in males. This change mimics associations between circulating leptin and bone mineral density (BMD) observed in adult humans. Osteoblast ObRb deletion using Col2.3-Cre did not produce a discernable bone phenotype. However, conditional removal of ObRb with Col3.6-Cre on more primitive MPCs increased femoral length and trabecular and cortical femoral parameters at 12 and 52 weeks of age. Our results imply that at physiologic equilibrium, leptin regulation of mature osteoblast function is negligible, however, early modulation of MPCs may contribute to properties such as bone length and trabecular formation. In contrast, regulation of myeloid lineage cells such as macrophages may explain adult gender-specific differences in associations between circulating leptin and BMD. Further modulation of macrophage-associated leptin signaling by compounds such as amino-bisphosphonates may enhance the ability of leptin to contribute to bone formation as well as the pathogenesis of diseases such as osteonecrosis of the jaw.Ph.D.Oral Health SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/89775/1/scheller_1.pd

Report from the 6th International Meeting on Bone Marrow Adiposity (BMA2020)

The

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

A neuroskeletal atlas: Spatial mapping and contextualization of axon subtypes innervating the long bones of C3H and B6 mice

Nerves in bone play well-established roles in pain and vasoregulation and have been associated with progression of skeletal disorders, including osteoporosis, fracture, arthritis, and tumor metastasis. However, isolation of the region-specific mechanisms underlying these relationships is limited by our lack of quantitative methods for neuroskeletal analysis and precise maps of skeletal innervation. To overcome these limitations, we developed an optimized workflow for imaging and quantitative analysis of axons in and around the bone, including validation of Baf53b-Cre in concert with R26R-tdTomato (Ai9) as a robust pan-neuronal reporter system for use in musculoskeletal tissues. In addition, we created comprehensive maps of sympathetic adrenergic and sensory peptidergic axons within and around the full length of the femur and tibia in two strains of mice (B6 and C3H). In the periosteum, these maps were related to the surrounding musculature, including entheses and myotendinous attachments to bone. Three distinct patterns of periosteal innervation (termed type I, II, III) were defined at sites that are important for bone pain, bone repair, and skeletal homeostasis. For the first time, our results establish a gradient of bone marrow axon density that increases from proximal to distal along the length of the tibia and define key regions of interest for neuroskeletal studies. Lastly, this information was related to major nerve branches and local maps of specialized mechanoreceptors. This detailed mapping and contextualization of the axonal subtypes innervating the skeleton is intended to serve as a guide during the design, implementation, and interpretation of future neuroskeletal studies and was compiled as a resource for the field as part of the NIH SPARC consortium. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Development, Disease, and Regeneration of Tissues in the Dental-Craniofacial Complex

This article has no abstract

Shared autonomic pathways connect bone marrow and peripheral adipose tissues across the central neuraxis

Bone marrow adipose tissue (BMAT) is increased in both obesity and anorexia. This is unique relative to white adipose tissue (WAT), which is generally more attuned to metabolic demand. It suggests that there may be regulatory pathways that are common to both BMAT and WAT and also those that are specific to BMAT alone. The central nervous system (CNS) is a key mediator of adipose tissue function through sympathetic adrenergic neurons. Thus, we hypothesized that central autonomic pathways may be involved in BMAT regulation. To test this, we first quantified the innervation of BMAT by tyrosine hydroxylase (TH) positive nerves within the metaphysis and diaphysis of the tibia of B6 and C3H mice. We found that many of the TH+ axons were concentrated around central blood vessels in the bone marrow. However, there were also areas of free nerve endings which terminated in regions of BMAT adipocytes. Overall, the proportion of nerve-associated BMAT adipocytes increased from proximal to distal along the length of the tibia (from ~3-5 to ~14-24%), regardless of mouse strain. To identify the central pathways involved in BMAT innervation and compare to peripheral WAT, we then performed retrograde viral tract tracing with an attenuated pseudorabies virus (PRV) to infect efferent nerves from the tibial metaphysis (inclusive of BMAT) and inguinal WAT (iWAT) of C3H mice. PRV positive neurons were identified consistently from both injection sites in the intermediolateral horn of the spinal cord, reticular formation, rostroventral medulla, solitary tract, periaqueductal gray, locus coeruleus, subcoeruleus, Barrington\u27s nucleus, and hypothalamus. We also observed dual-PRV infected neurons within the majority of these regions. Similar tracings were observed in pons, midbrain, and hypothalamic regions from B6 femur and tibia, demonstrating that these results persist across mouse strains and between skeletal sites. Altogether, this is the first quantitative report of BMAT autonomic innervation and reveals common central neuroanatomic pathways, including putative command neurons, involved in coordinating multiple aspects of sympathetic output and facilitation of parallel processing between bone marrow/BMAT and peripheral adipose tissue