Changes in skeletal integrity and marrow adiposity during high-fat diet and after weight loss

The prevalence of obesity has continued to rise over the past three decades leading to significant increases in obesity-related medical care costs from metabolic and non-metabolic sequelae. It is now clear that expansion of body fat leads to an increase in inflammation with systemic effects on metabolism. In mouse models of diet-induced obesity there is also an expansion of bone marrow adipocytes. However, the persistence of these changes after weight-loss has not been well described. The objective of this study was to investigate the impact of high-fat diet (HFD) and subsequent weight-loss on skeletal parameters in C57Bl6/J mice. Male mice were given a normal chow diet (ND) or 60% HFD at 6-weeks of age for 12-, 16-, or 20-weeks. A third group of mice was put on HFD for 12-weeks and then on ND for 8-weeks to mimic weight-loss. After these dietary challenges the tibia and femur were removed and analyzed by microCT for bone morphology. Decalcification followed by osmium staining was used to assess bone marrow adiposity and mechanical testing was performed to assess bone strength. After 12-, 16-, or 20-weeks of HFD, mice had significant weight gain relative to controls. Body mass returned to normal after weight-loss. Marrow adipose tissue (MAT) volume in the tibia increased after 16-weeks of HFD and persisted in the 20-week HFD group. Weight loss prevented HFD-induced MAT expansion. Trabecular bone volume fraction, mineral content, and number were decreased after 12-, 16-, or 20-weeks of HFD, relative to ND controls, with only partial recovery after weight-loss. Mechanical testing demonstrated decreased fracture resistance after 20-weeks of HFD. Loss of mechanical integrity did not recover after weight-loss. Our study demonstrates that HFD causes long-term, persistent changes in bone quality, despite prevention of marrow adipose tissue accumulation, as demonstrated through changes in bone morphology and mechanical strength in a mouse model of diet-induced obesity and weight-loss

Calcitonin Receptor Neurons in the Mouse Nucleus Tractus Solitarius Control Energy Balance via the Non-aversive Suppression of Feeding.

To understand hindbrain pathways involved in the control of food intake, we examined roles for calcitonin receptor (CALCR)-containing neurons in the NTS. Ablation of NTS Calcr abrogated the long-term suppression of food intake, but not aversive responses, by CALCR agonists. Similarly, activating CalcrNTS neurons decreased food intake and body weight but (unlike neighboring CckNTS cells) failed to promote aversion, revealing that CalcrNTS neurons mediate a non-aversive suppression of food intake. While both CalcrNTS and CckNTS neurons decreased feeding via projections to the PBN, CckNTS cells activated aversive CGRPPBN cells while CalcrNTS cells activated distinct non-CGRP PBN cells. Hence, CalcrNTS cells suppress feeding via non-aversive, non-CGRP PBN targets. Additionally, silencing CalcrNTS cells blunted food intake suppression by gut peptides and nutrients, increasing food intake and promoting obesity. Hence, CalcrNTS neurons define a hindbrain system that participates in physiological energy balance and suppresses food intake without activating aversive systems

Bone structure and function in male C57BL/6 mice: Effects of a high-fat Western-style diet with or without trace minerals

Purpose: Osteoporosis occurs in both women and men, but most of what we know about the condition comes from studies in females. The present study examined bone structure and function over an 18-month period in male C57BL/6 mice maintained on either a rodent chow diet (AIN76A) or a high-fat, Western-style diet (HFWD). Effects of mineral supplementation were assessed in both diets. Methods: Trabecular and cortical bone structure in femora and vertebrae were assessed by micro-CT analysis. Following this, bone stiffness and strength measurements were made. Finally, bone levels of several cationic trace elements were quantified, and serum biomarkers of bone metabolism evaluated. Results: Bone loss occurred over time in both diets but was more rapid and extensive in mice on the HFWD. Dietary mineral supplementation reduced bone loss in both diets and increased bone stiffness in the femora and bone stiffness and strength in the vertebrae. Bone content of strontium was increased in response to mineral supplementation in both diets. Conclusions: Bone loss was more severe in mice on the HFWD and mineral supplementation mitigated the effects of the HFWD. In comparison to previous findings with female C57BL/6 mice, the present studies indicate that males are more sensitive to diet and benefited from a healthy diet (AIN76A), while females lost as much bone on the healthy diet as on the HFWD. Male mice benefited from mineral supplementation, just as females did in the previous study. Keywords: Bone, Calcium, Cationic minerals, Strontium, Male mice, Osteoporosi

Sclerostin Antibody–Induced Changes in Bone Mass Are Site Specific in Developing Crania

Sclerostin antibody (Scl‐Ab) is an anabolic bone agent that has been shown to increase bone mass in clinical trials of adult diseases of low bone mass, such as osteoporosis and osteogenesis imperfecta (OI). Its use to decrease bone fragility in pediatric OI has shown efficacy in several growing mouse models, suggesting translational potential to pediatric disorders of low bone mass. However, the effects of pharmacologic inhibition of sclerostin during periods of rapid growth and development have not yet been described with respect to the cranium, where lifelong deficiency of functioning sclerostin leads to patterns of excessive bone growth, cranial compression, and facial palsy. In the present study, we undertook dimensional and volumetric measurements in the skulls of growing Brtl/+ OI mice treated with Scl‐Ab to examine whether therapy‐induced phenotypic changes were similar to those observed clinically in patients with sclerosteosis or Van Buchem disorder. Mice treated between 3 and 14 weeks of age with high doses of Scl‐Ab show significant calvarial thickening capable of rescuing OI‐induced deficiencies in skull thickness. Other changes in cranial morphology, such as lengths and distances between anatomic landmarks, intracranial volume, and suture interdigitation, showed minimal effects of Scl‐Ab when compared with growth‐induced differences over the treatment duration. Treatment‐induced narrowing of foramina was limited to sites of vascular but not neural passage, suggesting patterns of local regulation. Together, these findings reveal a site specificity of Scl‐Ab action in the calvaria with no measurable cranial nerve impingement or brainstem compression. This differentiation from the observed outcomes of lifelong sclerostin deficiency complements reports of Scl‐Ab treatment efficacy at other skeletal sites with the prospect of minimal cranial secondary complications. © 2019 American Society for Bone and Mineral Research. © 2019 American Society for Bone and Mineral Research.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152620/1/jbmr3858.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152620/2/jbmr3858_am.pd

Bone Chemical Composition Assessment with Multi-Wavelength Photoacoustic Analysis

In this study, the feasibility of assessing the chemical composition in bone using the multi-wavelength photoacoustic analysis (MWPA) method was investigated. By illuminating a bone specimen using laser light with a wavelength tunable over an optical spectrum from 680 nm to 950 nm, the optical absorption spectrum of the bone was acquired. Then, with the optical absorption spectra of all the optically absorbing chemical components in the bone known, a spectral unmixing procedure was performed to quantitatively assess the relative content of each chemical component. The experimental results from porcine rib bones demonstrated that the contents of the chemical components, including not only non-organic materials such as minerals and water but also organic materials including oxygenated hemoglobin, deoxygenated hemoglobin, lipid, and collagen, can all be assessed by MWPA. As the chemical composition in the bone is directly associated with functional and metabolic activities, the finding from this study suggests that the MWPA method could offer a new diagnostic tool for the non-invasive evaluation of bone health

Altered cytoskeletal organization characterized lethal but not surviving Brtl+/- mice: insight on phenotypic variability in osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a heritable bone disease with dominant and recessive transmission. It is characterized by a wide spectrum of clinical outcomes ranging from very mild to lethal in the perinatal period. The intra- and inter-familiar OI phenotypic variability in the presence of an identical molecular defect is still puzzling to the research field. We used the OI murine model Brtl(+/-) to investigate the molecular basis of OI phenotypic variability. Brtl(+/-) resembles classical dominant OI and shows either a moderately severe or a lethal outcome associated with the same Gly349Cys substitution in the α1 chain of type I collagen. A systems biology approach was used. We took advantage of proteomic pathway analysis to functionally link proteins differentially expressed in bone and skin of Brtl(+/-) mice with different outcomes to define possible phenotype modulators. The skin/bone and bone/skin hybrid networks highlighted three focal proteins: vimentin, stathmin and cofilin-1, belonging to or involved in cytoskeletal organization. Abnormal cytoskeleton was indeed demonstrated by immunohistochemistry to occur only in tissues from Brtl(+/-) lethal mice. The aberrant cytoskeleton affected osteoblast proliferation, collagen deposition, integrin and TGF-β signaling with impairment of bone structural properties. Finally, aberrant cytoskeletal assembly was detected in fibroblasts obtained from lethal, but not from non-lethal, OI patients carrying an identical glycine substitution. Our data demonstrated that compromised cytoskeletal assembly impaired both cell signaling and cellular trafficking in mutant lethal mice, altering bone properties. These results point to the cytoskeleton as a phenotypic modulator and potential novel target for OI treatment