Identification of a novel splice variant of the haloacid dehalogenase: PHOSPHO1

PHOSPHO1, a new member of the haloacid dehalogenase superfamily, has recently been implicated in the mineralization process in both osteoblasts and chondrocytes. In this study we describe the identification of a novel, alternatively spliced PHOSPHO1 transcript (PHOSPHO1-3a). This transcript contains the three exons of the previously published variant, however exon 3 contains a retained, 127bp section of intron 2. This forms an in-frame start site, producing an open reading frame of 879bp and predicting a protein of 292 amino acids. The novel 40 amino acid N-terminal region of PHOSPHO1-3a contains a relatively strong secretory signal, however all three domains of the HAD superfamily are retained in exon 3. The expression of this splice variant was confirmed in both human and mouse osteoblast-like cells and also in the chondrogenic ATDC5 cell line. The data within this study indicate a possible function relating to chondrocyte differentiation/mineralization as with the previously published variant

The CAGS-Snorkel mouse: A game changer in the identification of extracellular vesicles originating from cells of the osteogenic lineage.

The production and deposition of vesicles within the matrix by growth plate chondrocytes were first described over 50 years ago in a series of elegant electron microscopy studies by Clarke Anderson and Ermanno Bonucci (1, 2). These matrix vesicles (MVs) are membrane limited and offer a sheltered interior to promote calcium phosphate precipitation and are now recognised to be critical for biomineralization of both bone and cartilage matrix. Since these pioneering days it has become abundantly clear that many other types of extracellular vesicles (EVs), of varying size, composition and origin, are produced by cells, including osteoblasts, osteocytes, osteoclasts and chondrocytes. EVs is a catch-all term for a heterogenous population of vesicles released by cells and this includes exosomes which are released from cells after the fusion of multivesicular bodies with the plasma membrane, and ectosomes/microvesicles that are derived from the outward budding of the plasma membrane (3)

Mechanisms and Clinical Consequences of Vascular Calcification

Vascular calcification has severe clinical consequences and is considered an accurate predictor of future adverse cardiovascular events, including myocardial infarction and stroke. Previously vascular calcification was thought to be a passive process which involved the deposition of calcium and phosphate in arteries and cardiac valves. However, recent studies have shown that vascular calcification is a highly regulated, cell-mediated process similar to bone formation. In this article, we outline the current understanding of key mechanisms governing vascular calcification and highlight the clinical consequences. By understanding better the molecular pathways and genetic circuitry responsible for the pathological mineralization process novel drug targets may be identified and exploited to combat and reduce the detrimental effects of vascular calcification on human health

Suppressor of cytokine signaling 2 (SOCS2) deletion protects bone health of mice with DSS induced inflammatory bowel disease.

Individuals with inflammatory bowel disease (IBD) often present with poor bone health. The development of targeted therapies for this bone loss requires a fuller understanding of the underlying cellular mechanisms. Although bone loss in IBD is multifactorial the altered sensitivity and secretion of growth hormone (GH) and insulin-like growth factor-1 (IGF-1) in IBD is understood to be a critical contributing mechanism. The expression of suppressor of cytokine signaling 2 (SOCS2), a well-established negative regulator of GH signaling, is stimulated by pro-inflammatory cytokines. Therefore, it is likely that SOCS2 expression represents a critical mediator through which pro-inflammatory cytokines inhibit GH/IGF-1 signaling and decrease bone quality in IBD. Utilising the DSS model of colitis we have revealed that endogenously elevated GH function in the Socs2−/− mouse protects the skeleton from osteopenia. Micro-computed tomography assessment of DSS treated wild-type mice revealed a worsened trabecular architecture compared to control mice. Specifically, DSS treated WT mice had significantly decreased bone volume (BV/TV) (41%; p<0.05), trabecular thickness (16%; p<0.05), trabecular number (30%; p<0.05), and a resulting increase in trabecular separation (19%; <0.05). In comparison, the trabecular bone of Socs2 deficient mice was partially protected from the adverse effects of DSS. The reduction in a number of parameters including BV/TV (21%; p<0.05) was less, and no changes were observed in trabecular thickness or separation. This protected phenotype was unlikely to be a consequence of improved mucosal health in the DSS treated Socs2−/− mice but rather a result of unregulated GH signaling directly on bone. These studies indicate that the absence of SOCS2 is protective against bone loss typical of IBD. This study also provides an improved understanding of the relative effects of GH/IGF-1 on bone health in experimental colitis, information that is essential before these drugs are explored as bone protective agents in children and adults with IBD

Skeletal energy homeostasis:a paradigm of endocrine discovery

Throughout the last decade, significant developments in cellular, molecular and mouse models have revealed major endocrine functions of the skeleton. More recent studies have evolved the interplay between bone-specific hormones, the skeleton, marrow adipose tissue, muscle and the brain. This review focuses on literature from the last decade, addressing the endocrine regulation of global energy metabolism via the skeleton. In addition, we will highlight several recent studies that further our knowledge of new endocrine functions of some organs; explore remaining unanswered questions; and, finally, we will discuss future directions for this more complex era of bone biology research.</jats:p

The presence of PHOSPHO1 in matrix vesicles and its developmental expression prior to skeletal mineralization

PHOSPHO1 is a phosphoethanolamine/phosphocholine phosphatase that has previously been implicated in generating inorganic phosphate (Pi) for matrix mineralization. In this study, we have investigated PHOSPHO1 mRNA expression during embryonic development in the chick. Whole-mount in situ hybridization indicated that PHOSPHO1 expression occurred prior to E6.5 and was initially restricted to the bone collar within the mid-shaft of the diaphysis of long bones but by E11.5 expression was observed over the entire length of the diaphysis. Alcian blue/alizarin red staining revealed that PHOSPHO1 expression seen in the primary regions of ossification preceded the deposition of mineral, suggesting that it is involved in the initial events of mineral formation. We isolated MVs from growth plate chondrocytes and confirmed the presence of high levels of PHOSPHO1 by immunoblotting. Expression of PHOSPHO1, like TNAP activity, was found to be up-regulated in MVs isolated from chondrocytes induced to differentiate by the addition of ascorbic acid. This suggests that both enzymes may be regulated by similar mechanisms. These studies provide for the first time direct evidence that PHOSPHO1 is present in MVs, and its developmental expression pattern is consistent with a role in the early stages of matrix mineralization