Osteoporosis in longstanding acromegaly: characteristic changes of vertebral trabecular architecture and bone matrix composition

Multiscale molecular profiling of pathological bone resolves sexually dimorphic control of extracellular matrix composition

Collagen assembly during development is essential for successful matrix mineralisation, which determines bone quality and mechanocompetence. However, the biochemical and structural perturbations that drive pathological skeletal collagen configuration remain unclear. Deletion of vascular endothelial growth factor (VEGF; also known as VEGFA) in bone-forming osteoblasts (OBs) induces sex-specific alterations in extracellular matrix (ECM) conformation and mineralisation coupled to vascular changes, which are augmented in males. Whether this phenotypic dimorphism arises as a result of the divergent control of ECM composition and its subsequent arrangement is unknown and is the focus of this study. Herein, we used murine osteocalcin-specific Vegf knockout (OcnVEGFKO) and performed ex vivo multiscale analysis at the tibiofibular junction of both sexes. Label-free and non-destructive polarisation-resolved second-harmonic generation (p-SHG) microscopy revealed a reduction in collagen fibre number in males following the loss of VEGF, complemented by observable defects in matrix organisation by backscattered electron scanning electron microscopy. This was accompanied by localised divergence in collagen orientation, determined by p-SHG anisotropy measurements, as a result of OcnVEGFKO. Raman spectroscopy confirmed that the effect on collagen was linked to molecular dimorphic VEGF effects on collagen-specific proline and hydroxyproline, and collagen intra-strand stability, in addition to matrix carbonation and mineralisation. Vegf deletion in male and female murine OB cultures in vitro further highlighted divergence in genes regulating local ECM structure, including Adamts2, Spp1, Mmp9 and Lama1. Our results demonstrate the utility of macromolecular imaging and spectroscopic modalities for the detection of collagen arrangement and ECM composition in pathological bone. Linking the sex-specific genetic regulators to matrix signatures could be important for treatment of dimorphic bone disorders that clinically manifest in pathological nano- and macro-level disorganisation. This article has an associated First Person interview with the first author of the paper.

Unilateral atlantal mass hypertrophy in acromegaly

The authors report an extremely rare case of a patient with acromegaly who had unilateral enlargement of an atlas facet resulting in cord compression and progressive quadriparesis. Although unilateral atlas facet enlargement has been identified in the literature in cases of spondylosis and as a component of congenital malformation, its association with acromegaly has not previously been reported. Resection of the offending facetal bone and atlantoaxial fixation resulted in rapid neurological recovery.

Bone architecture: collagen structure and calcium/phosphorus maps

Bone collagen structure in normal and pathological tissues is presented using techniques of thin section transmission electron microscopy and morphometry. In pathological tissue, deviations from normal fine structure are reflected in abnormal arrangements of collagen fibrils and abnormalities in fibril diameter. The relationships between these bone structural changes and the skeletal calcium/phosphorus ratio are discussed. Calcium/phosphorus ratio is measured by X-ray absorptiometry and computed microtomography.

The role of collagen in bone structure: An image processing approach

Bone collagen structure in normal and pathological tissues is illustrated using techniques of thin section transmission electron microscopy and computer-assisted analysis. The normal bone collagen types, fibril architecture and diameter are described. In pathological tissue, deviations from normal fine structure are reflected in abnormal arrangements of collagen fibrils and abnormalities in fibril diameter. Computer analyses of normal fibril positive staining patterns are presented in order to provide a basis for comparing such patterns with pathological ones.

A new method of comprehensive static histomorphometry applied on human lumbar vertebral cancellous bone

The aim of the present study was to assess age-related changes in the human spine by use of established static histomorphometry, and to determine how these static histomorphometric measures are interrelated in human cancellous bone tissue. The material comprised normal human lumbar vertebral bodies (L-2) from 12 women (19-96 years) and 12 men (23-91 years) selected from a larger autopsy material to give an even age and gender distribution. In addition, L-2 from three female subjects (80, 88, and 90 years) with a known vertebral fracture of L-2 were considered. Approximately 9-mm-thick frontal (mediolateral) slices were embedded in methylmetacrylate, stained with aniline blue, and scanned into a computer with a flatbed image scanner at a high resolution (2400 dpi). With a custom-made computer program the following static histomorphometric measures were determined: trabecular bone volume; marrow space star volume; bone space star volume; anisotropy of bone and marrow phase (star length distribution method); node-strut analysis (node:terminus ratio); trabecular thickness; trabecular number; trabecular separation; and trabecular bone pattern factor. In addition, connectivity density was determined (by the ConnEulor method). All 11 histomorphometric measures, except bone space star volume and the two measures of anisotropy, showed a significant correlation with age. Marrow space star volume (r = 0.82) and trabecular bone volume (r = -0.81) showed the highest correlation with age. Furthermore, it was found that all of the histomorphometric measures were correlated, to different degrees. Trabecular bone volume correlated significantly with all ten histomorphometric measures, whereas the two anisotropy measures were poorly correlated to the other measures. Finally, we found the histomorphometric values in this study to be in excellent accordance with various previously published results from studies of human trabecular vertebral bone, the sole exception being marrow space star volume, which was probably due to the small (artificial) region of interest (ROI) that was used in the earlier studies. In conclusion, the new method applied herein allows for easy assessment of age-related changes and also for assessment of relationships between histomorphometric measures in human vertebral cancellous bone.

Systemic over-secretion of growth hormone in transgenic mice results in a specific pattern of skeletal modeling and adaptation

The effects of growth hormone (GH) over-secretion on bone modeling and remodeling in transgenic mice were investigated using systematic and hierarchical methods. The results showed that continual systemic stimulation of GH over-secretion in mice resulted in an initial increase in bone mass, but its bone quality was not comparable with that of the littermate controls. Further continual over-stimulation of GH resulted in an increase in bone resorption leading to thinner cortices with inferior tissue mechanical properties. Three biological mechanisms following GH over-production are formulated to explain the observed results: GH over-secretion stimulated the production of inferior bone matrices, i.e., woven bone and cartilage, in addition to the production of normal lamellar bone; the increased bone formation stimulated by GH was followed by an exaggerated bone resorption process, resulting in cortical tissue with inferior mechanical properties; and a cortical shift occurred following GH over-stimulation that appeared to be caused by the combined effects of GH over-secretion and a variation in mechanical stimuli in the metallothionein-1 growth hormone regulating hormone transgenic mice. An "Optimal Strain Environment" model is proposed to help explain the observed results. From the results of the present and previous studies, we believe that the primary goal of bone adaptation to a biological perturbation, at least in mice, is to ensure proper mechanical function by maintaining structural integrity. In the process of maintaining a targeted whole bone structural integrity, the mechanical integrity of tissue may be sacrificed.