A bone-specific adipogenesis pathway in fat-free mice defines key origins and adaptations of bone marrow adipocytes with age and disease

Bone marrow adipocytes accumulate with age and in diverse disease states. However, their origins and adaptations in these conditions remain unclear, impairing our understanding of their context-specific endocrine functions and relationship with surrounding tissues. In this study, by analyzing bone and adipose tissues in the lipodystrophic ‘fat-free’ mouse, we define a novel, secondary adipogenesis pathway that relies on the recruitment of adiponectin-negative stromal progenitors. This pathway is unique to the bone marrow and is activated with age and in states of metabolic stress in the fat-free mouse model, resulting in the expansion of bone marrow adipocytes specialized for lipid storage with compromised lipid mobilization and cytokine expression within regions traditionally devoted to hematopoiesis. This finding further distinguishes bone marrow from peripheral adipocytes and contributes to our understanding of bone marrow adipocyte origins, adaptations, and relationships with surrounding tissues with age and disease.

Bone marrow adipose tissue does not express UCP1 during development or adrenergic-induced remodeling

Adipocytes within the skeleton are collectively termed bone marrow adipose tissue (BMAT). BMAT contributes to peripheral and local metabolism, however, its capacity for cell-autonomous expression of uncoupling protein 1 (UCP1), a biomarker of beige and brown adipogenesis, remains unclear. To overcome this, Ucp1-Cre was used to drive diphtheria toxin expression in cells expressing UCP1 (Ucp1Cre+/DTA+). Despite loss of brown adipose tissue, BMAT volume was not reduced in Ucp1Cre+/DTA+ mice. Comparably, in mTmG reporter mice (Ucp1Cre+/mTmG+), Ucp1-Cre expression was absent from BMAT in young (3-weeks) and mature (16-weeks) male and female mice. Further, β3-agonist stimulation failed to induce Ucp1-Cre expression in BMAT. This demonstrates that BMAT adipocytes are not UCP1-expressing beige/brown adipocytes. Thus, to identify novel and emerging roles for BMAT adipocytes in skeletal and whole-body homeostasis, we performed gene enrichment analysis of microarray data from adipose tissues of adult rabbits. Pathway analysis revealed genetic evidence for differences in BMAT including insulin resistance, decreased fatty acid metabolism, and enhanced contributions to local processes including bone mineral density through candidate genes such as osteopontin. In sum, this supports a paradigm by which BMAT adipocytes are a unique subpopulation that is specialized to support cells within the skeletal and hematopoietic niche.

Characterization of the bone marrow adipocyte niche with three-dimensional electron microscopy

Unlike white and brown adipose tissues, the bone marrow adipocyte (BMA) exists in a microenvironment containing unique populations of hematopoietic and skeletal cells. To study this microenvironment at the sub-cellular level, we performed a three-dimensional analysis of the ultrastructure of the BMA niche with focused ion beam scanning electron microscopy (FIB-SEM). This revealed that BMAs display hallmarks of metabolically active cells including polarized lipid deposits, a dense mitochondrial network, and areas of endoplasmic reticulum. The distinct orientations of the triacylglycerol droplets suggest that fatty acids are taken up and/or released in three key areas - at the endothelial interface, into the hematopoietic milieu, and at the bone surface. Near the sinusoidal vasculature, endothelial cells send finger-like projections into the surface of the BMA which terminate near regions of lipid within the BMA cytoplasm. In some regions, perivascular cells encase the BMA with their flattened cellular projections, limiting contacts with other cells in the niche. In the hematopoietic milieu, BMAT adipocytes of the proximal tibia interact extensively with maturing cells of the myeloid/granulocyte lineage. Associations with erythroblast islands are also prominent. At the bone surface, the BMA extends organelle and lipid-rich cytoplasmic regions toward areas of active osteoblasts. This suggests that the BMA may serve to partition nutrient utilization between diverse cellular compartments, serving as an energy-rich hub of the stromal-reticular network. Lastly, though immuno-EM, we've identified a subset of bone marrow adipocytes that are innervated by the sympathetic nervous system, providing an additional mechanism for regulation of the BMA. In summary, this work reveals that the bone marrow adipocyte is a dynamic cell with substantial capacity for interactions with the diverse components of its surrounding microenvironment. These local interactions likely contribute to its unique regulation relative to peripheral adipose tissues.

Bone marrow adipocytes resist lipolysis and remodeling in response to β-adrenergic stimulation

Bone marrow adipose tissue (BMAT) is preserved or increased in states of caloric restriction. Similarly, we found that BMAT in the tail vertebrae, but not the red marrow in the tibia, resists loss of neutral lipid with acute, 48-hour fasting in rats. The mechanisms underlying this phenomenon and its seemingly distinct regulation from peripheral white adipose tissue (WAT) remain unknown. To test the role of β-adrenergic stimulation, a major regulator of adipose tissue lipolysis, we examined the responses of BMAT to β-adrenergic agonists. Relative to inguinal WAT, BMAT had reduced phosphorylation of hormone sensitive lipase (HSL) after treatment with pan-β-adrenergic agonist isoproterenol. Phosphorylation of HSL in response to β3-adrenergic agonist CL316,243 was decreased by an additional ~90% (distal tibia BMAT) or could not be detected (tail vertebrae). Ex vivo, adrenergic stimulation of lipolysis in purified BMAT adipocytes was also substantially less than iWAT adipocytes and had site-specific properties. Specifically, regulated bone marrow adipocytes (rBMAs) from proximal tibia and femur underwent lipolysis in response to both CL316,243 and forskolin, while constitutive BMAs from the tail responded only to forskolin. This occurred independently of changes in gene expression of β-adrenergic receptors, which were similar between adipocytes from iWAT and BMAT, and could not be explained by defective coupling of β-adrenergic receptors to lipolytic machinery through caveolin 1. Specifically, we found that whereas caveolin 1 was necessary to mediate maximal stimulation of lipolysis in iWAT, overexpression of caveolin 1 was insufficient to rescue impaired BMAT signaling. Lastly, we tested the ability of BMAT to respond to 72-hour treatment with CL316,243 in vivo. This was sufficient to cause beiging of iWAT adipocytes and a decrease in iWAT adipocyte cell size. By contrast, adipocyte size in the tail BMAT and distal tibia remained unchanged. However, within the distal femur, we identified a subpopulation of BMAT adipocytes that underwent lipid droplet remodeling. This response was more pronounced in females than in males and resembled lipolysis-induced lipid partitioning rather than traditional beiging. In summary, BMAT has the capacity to respond to β-adrenergic stimuli, however, its responses are muted and BMAT generally resists lipid hydrolysis and remodeling relative to iWAT. This resistance is more pronounced in distal regions of the skeleton where the BMAT adipocytes are larger with little intervening hematopoiesis, suggesting that there may be a role for both cell-autonomous and microenvironmental determinants. Resistance to β-adrenergic stimuli further separates BMAT from known regulators of energy partitioning and contributes to our understanding of why BMAT is preserved in states of fasting and caloric restriction.

PERMANENT GENETIC RESOURCES: Isolation and characterization of 12 microsatellite markers in the middle-spotted woodpecker (Dendrocopos medius)

Twelve polymorphic microsatellite loci were developed for Dendrocopos medius. Polymorphism was assessed for 27 individuals from the southwesternmost population of this woodpecker species. The number of alleles per locus ranged from three to seven, with observed heterozygosity values from 0.444 to 0.852. Genotypic frequencies conformed to Hardy-Weinberg equilibrium, and no evidence for linkage disequilibrium was observed. Multilocus genotypes resulting from this set of markers will be useful to determine genetic diversity and differentiation within and among habitat patches inhabited by D. medius. Three of the loci were polymorphic for Picoides articus.

The effects of acupressure on the incidence of postoperative nausea and vomiting in postsurgical patients

Postoperative nausea and vomiting (PONV) is one of the most common postoperative complications. Aside from pharmacological interventions, other complementary healing modalities have been introduced to assist patients in decreasing PONV and improving postoperative outcomes. This study examined acupressure as a potentially holistic and safe complement to the more traditional approach of using drugs to prevent and/or relieve nausea and vomiting in the postoperative patient. Acupressure involves constant pressure (without puncture of the skin) on the Nei Guan acupuncture points through the use of a British product called Sea-Bands (Sea Band UK Ltd, Leics, England). These bands are made of elasticated fabric, with a small round plastic button inside. A quasi-experimental research design was used to examine the effects of unilateral and bilateral application of acupressure on 157 patients who are prone to PONV: postgynecological, postplastic, and posturological surgery patients. The incidence of PONV was determined through retrospective chart reviews. The hypothesis was that there would be a difference in the incidence of PONV between 5 groups: group 1 (Sea-Bands with acupressure on both wrists), group 2 (Sea-Bands with acupressure on one wrist), group 3 (wristband without acupressure on both wrists), group 4 (wristband without acupressure on one wrist), and group 5 (no wristband). This hypothesis was examined by using a one-way analysis of variance (ANOVA); it was not supported. Neither unilateral nor bilateral application of acupressure significantly affected the incidence of nausea and vomiting. These findings must be viewed with caution, however, because power analysis showed low effect sizes and an inadequate sample size. Further research is recommended with a larger sample size. This study has made perianesthesia nurses more aware of other complementary modalities to assist patients with nausea and vomiting.

A between-subjects comparison of respiratory sinus arrhythmia and baroreceptor cardiac reflex sensitivity as non-invasive measures of tonic parasympathetic cardiac control

Respiratory sinus arrhythmia (RSA) has been used as an index of parasympathetic cardiac control. However, recent psychophysiological research casts serious doubts upon the usefulness of RSA as an index of vagal influences upon the heart in psychophysiological as well as in clinical studies. It suggests the need to look for another measure. In this exploratory study we investigated whether the baroreflex sensitivity (BRS) could serve as an alternative tool to investigate between-subject tonic parasympathetic influences on the heart. In nine healthy subjects we examined the effects of intravenous atropine (0.03 mg/kg i.v.), intravenous metoprolol (10-15 mg i.v.), and of saline as a placebo condition upon RSA, BRS, and related cardiovascular and respiratory variables, both under resting and under mental task conditions. After parasympathetic blockade, RSA and BRS display values near zero, showing their vagal origin. After beta-adrenergic blockade, when heart period is predominantly under vagal control, RSA fails to predict heart period variability. Using BRS, however, it is possible to predict more than 97% of heart period variance during beta-blockade. Finally, both the vagal and beta-adrenergic blockade show that BRS is a better predictor of parasympathetic cardiac control during blood pressure increases than during blood pressure decreases.

Concurrent cerebral venous sinus thrombosis and myeloradiculopathy in Sjögren's syndrome

A 41-year-old woman complained of severe headaches and developed quadriparesis and neurogenic bladder. Evaluation disclosed the presence of Sjögren's syndrome complicated by myeloradiculopathy with MRI evidence of cervical cord involvement. Concurrent cerebral venous sinus thrombosis was also noted. Treatment with steroids and warfarin led to clinical improvement and resolution of MRI findings.