Bone Nanomechanical Properties and Relationship to Bone Turnover and Architecture in Patients With Atypical Femur Fractures: A Prospective Nested Case-Control Study

AUTHORS

Lanny V. Griffin,Elizabeth Warner,Saroj Palnitkar,Shijing Qiu,Mahalakshmi Honasoge,Shawna G. Griffin,George Divine,Sudhaker D. Rao

ABSTRACT

Atypical femur fractures (AFFs) are well-established serious complication of long-term bisphosphonate and denosumab therapy in patients with osteopenia or osteoporosis. To elucidate underlying mechanism(s) for the development of AFF, we performed a nested case-control study to investigate bone tissue nanomechanical properties and prevailing bone microstructure and tissue-level remodeling status as assessed by bone histomorphometry. We hypothesized that there would be differences in nanomechanical properties between patients with and without AFF and that bone microstructure and remodeling would be related to nanomechanical properties. Thirty-two full-thickness transiliac bone biopsies were obtained from age- and sex-matched patients on long-term bisphosphonate therapy with (n = 16) and without an AFF (n = 16). Standard histomorphometric measurements were made in each sample on three different bone envelopes (cancellous, intracortical, and endosteal). Iliac bone wall thickness was significantly lower on all three bone surfaces in patients with AFF than in those without AFF. Surface-based bone formation rate was suppressed similarly in both groups in comparison to healthy premenopausal and postmenopausal women, with no significant difference between the two groups. Nanoindentation was used to assess material properties of cortical and cancellous bone separately. Elastic modulus was higher in cortical than in cancellous bone in patients with AFF as well as compared to the elastic modulus of cortical bone from non-AFF patients. However, the elastic modulus of the cancellous bone was not different between AFF and non-AFF groups or between cortical and cancellous bone of non-AFF patients. Resistance to plastic deformation was decreased in cortical bone in both AFF and non-AFF groups compared to cancellous bone, but to a greater extent in AFF patients. We conclude that long-term bisphosphonate therapy is associated with prolonged suppression of bone turnover resulting in altered cortical remodeling and tissue nanomechanical properties leading to AFF.

The alarmin interleukin-1α triggers secondary degeneration through reactive astrocytes and endothelium after spinal cord injury

AUTHORS

Floriane Bretheau, Adrian Castellanos-Molina, Benoit Mailhot, Maxime Kusik, Dominic Belanger, Martine Lessard, Nicolas Vallières, Xiaoyu Liu, Ning Quan, Steve Lacroix

ABSTRACT

Spinal cord injury (SCI) triggers neuroinflammation, and subsequently secondary degeneration and oligodendrocyte (OL) death. We report that the alarmin interleukin (IL)-1α is released by damaged microglia after SCI. Intra-cisterna magna injection of IL-1α in mice rapidly induced neutrophil infiltration and OL death throughout the spinal cord, mimicking what is seen at sites of SCI. These effects were abolished by co-treatment with the IL-1R1 antagonist anakinra, as well as in IL-1R1-knockout mice which showed enhanced locomotor recovery after SCI. Conditional restoration of IL-1R1 expression in astrocytes or endothelial cells (ECs), but not in OLs or microglia, restored IL-1α-induced effects, while astrocyte- or EC-specific Il1r1 deletion reduced OL loss. Conditioned medium derived from IL-1α-stimulated astrocytes is toxic for OLs; further, IL-1α-stimulated astrocytes generate reactive oxygen species (ROS) and blocking ROS production in IL-1α-treated or SCI mice prevented OL loss. Thus, after SCI, microglia release IL-1α, which induces astrocyte- and EC-mediated OL degeneration.

WNT7B overexpression rescues bone loss caused by glucocorticoids in mice

AUTHORS

Hong Chen, Fangfang Song, Fanxin Long

ABSTRACT

Glucocorticoids, widely prescribed for anti-inflammatory and immunosuppressive purposes, are the most common secondary cause for osteoporosis and related fractures. Current anti-resorptive and anabolic therapies are insufficient for treating glucocorticoid-induced osteoporosis due to contraindications or concerns of side effects. Glucocorticoids have been shown to disrupt Wnt signaling in osteoblast-lineage cells, but the efficacy for Wnt proteins to restore bone mass after glucocorticoid therapy has not been examined. Here by using two mouse genetic models wherein WNT7B expression is temporally activated by either tamoxifen or doxycycline in osteoblast-lineage cells, we show that WNT7B recovers bone mass following glucocorticoid-induced bone loss, thanks to increased osteoblast number and function. However, WNT7B overexpression in bone either before or after glucocorticoid treatments does not ameliorate the abnormal accumulation of body fat. The study demonstrates a potent bone anabolic function for WNT7B in countering glucocorticoid-induced bone loss.

Nerve transfer for restoration of lower motor neuron-lesioned bladder function. Part 2: correlation between histological changes and nerve evoked contractions

AUTHORS

Mary F. Barbe, Courtney L. Testa, Geneva E. Cruz, Nagat A. Frara, Ekta Tiwari, Lucas J. Hobson, Brian S. McIntyre, Danielle S. Porreca, Dania Giaddui, Alan S. Braverman, Emily P. Day, Mamta Amin, Justin M. Brown, Michael Mazzei, Michel A. Pontari, Ida J. Wagner, and Michael R. Ruggieri Sr.

ABSTRACT

We determined the effect of pelvic organ decentralization and reinnervation 1 yr later on urinary bladder histology and function. Nineteen canines underwent decentralization by bilateral transection of all coccygeal and sacral (S) spinal roots, dorsal roots of lumbar (L)7, and hypogastric nerves. After exclusions, eight were reinnervated 12 mo postdecentralization with obturator-to-pelvic and sciatic-to-pudendal nerve transfers, then euthanized 8-12 mo later. Four served as long-term decentralized only animals. Before euthanasia, pelvic or transferred nerves and L1–S3 spinal roots were stimulated and maximum detrusor pressure (MDP) recorded. Bladder specimens were collected for histological and ex vivo smooth muscle contractility studies. Both reinnervated and decentralized animals showed less or denuded urothelium, fewer intramural ganglia, and more inflammation and collagen, than controls, although percent muscle was maintained. In reinnervated animals, pgp9.5+ axon density was higher compared with decentralized animals. Ex vivo smooth muscle contractions in response to KCl correlated positively with submucosal inflammation, detrusor muscle thickness, and pgp9.5+ axon density. In vivo, reinnervated animals showed higher MDP after stimulation of L1–L6 roots compared with their transected L7–S3 roots, and reinnervated and decentralized animals showed lower MDP than controls after stimulation of nerves (due likely to fibrotic nerve encapsulation). MDP correlated negatively with detrusor collagen and inflammation, and positively with pgp9.5+ axon density and intramural ganglia numbers. These results demonstrate that bladder function can be improved by transfer of obturator nerves to pelvic nerves at 1 yr after decentralization, although the fibrosis and inflammation that developed were associated with decreased contractile function.

Type 1 diabetic Akita mice have low bone mass and impaired fracture healing

AUTHORS

Pei Hu, Jennifer A. McKenzie, Evan G. Buettmann, Nicole Migotsky, Michael J. Gardner, Matthew J.Silva

ABSTRACT

Type 1 diabetes (T1DM) impairs bone formation and fracture healing in humans. Akita mice carry a mutation in one allele of the insulin-2 (Ins2) gene, which leads to pancreatic beta cell dysfunction and hyperglycemia by 5–6 weeks age. We hypothesized that T1DM in Akita mice is associated with decreased bone mass, weaker bones, and impaired fracture healing. Ins2 ± (Akita) and wildtype (WT) males were subjected to femur fracture at 18-weeks age and healing assessed 3–21 days post-fracture. Non-fractured left femurs were assessed for morphology (microCT) and strength (bending or torsion) at 19–21 weeks age. Fractured right femurs were assessed for callus mechanics (torsion), morphology and composition (microCT and histology) and gene expression (qPCR). Both Akita and WT mice gained weight from 3 to 18 weeks age, but Akita mice weighed less starting at 5 weeks (−5.2%, p < 0.05). At 18–20 weeks age Akita mice had reduced serum osteocalcin (−30%), cortical bone area (−16%), and thickness (−17%) compared to WT, as well as reduced cancellous BV/TV (−39%), trabecular thickness (−23%) and vBMD (−31%). Mechanical testing of non-fractured femurs showed decreased structural (stiffness, ultimate load) and material (ultimate stress) properties of Akita bones. At 14 and 21 days post fracture Akita mice had a significantly smaller callus than WT mice (~30%), with less cartilage and bone area. Assessment of torsional strength showed a weaker callus in Akita mice with lower stiffness (−42%), maximum torque (−44%) and work to fracture (−44%). In summary, cortical and cancellous bone mass were reduced in Akita mice, with lower bone mechanical properties. Fracture healing in Akita mice was impaired by T1DM, with a smaller, weaker fracture callus due to decreased cartilage and bone formation. In conclusion, the Akita mouse mimics some of the skeletal features of T1DM in humans, including osteopenia and impaired fracture healing, and may be useful to test interventions.

WNT16 is Robustly Increased by Oncostatin M in Mouse Calvarial Osteoblasts and Acts as a Negative Feedback Regulator of Osteoclast Formation Induced by Oncostatin M

AUTHORS

Henning P, Movérare-Skrtic S, Westerlund A, Souza PPC, Floriano-Marcelino T , Nilsson KH, El Shahawy M , Ohlsson C, Lerner UH

ABSTRACT

Background: Bone loss is often observed adjacent to inflammatory processes. The WNT signaling pathways have been implicated as novel regulators of both immune responses and bone metabolism. WNT16 is important for cortical bone mass by inhibiting osteoclast differentiation, and we have here investigated the regulation of WNT16 by several members of the pro-inflammatory gp130 cytokine family.

Methods: The expression and regulation of Wnt16 in primary murine cells were studied by qPCR, scRNAseq and in situ hybridization. Signaling pathways were studied by siRNA silencing. The importance of oncostatin M (OSM)-induced WNT16 expression for osteoclastogenesis was studied in cells from Wnt16-deficient and wild-type mice.

Results: We found that IL-6/sIL-6R and OSM induce the expression of Wnt16 in primary mouse calvarial osteoblasts, with OSM being the most robust stimulator. The induction of Wnt16 by OSM was dependent on gp130 and OSM receptor (OSMR), and downstream signaling by the SHC1/STAT3 pathway, but independent of ERK. Stimulation of the calvarial cells with OSM resulted in enhanced numbers of mature, oversized osteoclasts when cells were isolated from Wnt16 deficient mice compared to cells from wild-type mice. OSM did not affect Wnt16 mRNA expression in bone marrow cell cultures, explained by the finding that Wnt16 and Osmr are expressed in distinctly different cells in bone marrow, nor was osteoclast differentiation different in OSM-stimulated bone marrow cell cultures isolated from Wnt16−/- or wild-type mice. Furthermore, we found that Wnt16 expression is substantially lower in cells from bone marrow compared to calvarial osteoblasts.

Conclusion: These findings demonstrate that OSM is a robust stimulator of Wnt16 mRNA in calvarial osteoblasts and that WNT16 acts as a negative feedback regulator of OSM-induced osteoclast formation in the calvarial bone cells, but not in the bone marrow.