Endochondral ossification, an important bone formation process in vertebrates, highly depends on proper functioning of growth plate chondrocytes 1 . Their proliferation determines longitudinal bone growth and the matrix deposited provides a scaffold for future bone formation. However, these two energy-dependent anabolic processes occur in an avascular environment 1,2 . In addition, the centre of the expanding growth plate becomes hypoxic and local activation of the hypoxiainducible transcription factor HIF-1α is necessary for chondrocyte survival by still unknown cellintrinsic mechanisms [3][4][5][6] . Whether HIF-1α signalling has to be contained in the other regions of the growth plate and whether chondrocyte metabolism controls cell function remains undefined. We here show that prolonged HIF-1α signalling in chondrocytes leads to skeletal dysplasia by interfering with cellular bioenergetics and biosynthesis. Decreased glucose oxidation results in an energy deficit, which limits proliferation, activates the unfolded protein response (UPR) and reduces collagen synthesis. However, enhanced glutamine flux increases α-ketoglutarate (αKG) levels, which in turn increases collagen proline and lysine hydroxylation. This metabolically regulated collagen modification renders the cartilaginous matrix more resistant to proteasemediated degradation and thereby increases bone mass. Thus, inappropriate HIF-1α signalling results in skeletal dysplasia caused by collagen overmodification, an effect that may also contribute to other extracellular matrix-related diseases such as cancer and fibrosis.To investigate whether HIF signalling needs to be controlled in growth plate chondrocytes, we conditionally inactivated HIF prolyl hydroxylase 2 (PHD2; Phd2 chonmice), its main negative regulator 7 , resulting in HIF-1α accumulation (Extended Data Fig. 1a-d).This approach caused skeletal dysplasia, characterized by impaired longitudinal bone growth and increased trabecular bone mass (Fig. 1a,b, Extended Data Fig. 1e,f). The growth plate was shorter, but normally organized and, interestingly, the high bone mass was not due to altered bone resorption or formation (Extended Data Fig. 1g-l). Instead, we observed more cartilage remnants in the bony trabeculae, evidenced by more type II collagen (COL2)positive and proteoglycan-rich matrix (Fig. 1c, Extended Data Fig. 1m). The decreased serum CTx-II levels, measuring COL2 degradation, indicated that the cartilage matrix was incompletely resorbed, and the unaltered chondrocyte-to-matrix ratio pointed to a qualitative, rather than quantitative, change in matrix properties (Extended Data Fig. 1j,n). Thus, inactive oxygen sensing in chondrocytes increases trabecular bone mass, caused by abundant cartilage remnants, likely resulting from modifications in the cartilage matrix itself.HIF-1α stabilization in PHD2-deficient chondrocytes resulted, as expected 7,8 , in metabolic reprogramming. Mitochondrial content was reduced, likely because of decreased biogenesis without changing autophagy (Extended D...

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Calcium phosphate cements (CPCs) are commonly used as bone substitute materials. However, their slow degradation rate and lack of macroporosity hinders new bone formation. Poly(dl-lactic-co-glycolic acid) (PLGA) incorporation is of great interest as, upon degradation, produces acidic by-products that enhance CPC degradation. Yet, new bone formation is delayed until PLGA degradation occurs a few weeks after implantation. Therefore, the aim of this study was to accelerate the early stage pore formation within CPCs in vitro. With that purpose, we incorporated the water-soluble porogen sucrose at different weight percentages (10 or 20 wt %) to CPC and CPC/PLGA composites. The results revealed that incorporation of sucrose porogens increased mass loss within the first week of in vitro degradation in groups containing sucrose compared to control groups. After week 1, a further mass loss was observed related to PLGA and CPC degradation. Macroporosity analysis confirmed that macroporosity formation is influenced by the dissolution of sucrose at an early stage and by the degradation of PLGA and CPC at a later stage. We concluded that the combination of sucrose and PLGA porogens in CPC is a promising approach to promote early stage bone tissue ingrowth and complete replacement of CPC through multimodal pore formation. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 500-509, 2018.

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Smads are intracellular signaling proteins that transduce signals elicited by members of the transforming growth factor (TGF)-␤ superfamily. Smad5 and Smad1 are highly homologous, and they mediate primarily bone morphogenetic protein (Bmp) signals. We used the Cre-loxP system and Sm22-Cre and Tie-1-Cre mice to study the function of Smad5 in the developing blood vessel wall. Analysis of embryos demonstrated that deletion of Smad5 in endothelial or smooth muscle cells resulted in a normal organization of embryonic and extra-embryonic vasculature. Angiogenic assays performed in adult mice revealed that mutant mice display a comparable angiogenic and vascular remodeling response to control mice. In Sm22-Cre; Smad5 fl/؊ mice, Smad5 is also deleted in cardiomyocytes. Echocardiographic analysis on those 9-monthold female mice demonstrated larger left ventricle internal diameters and decreased fractional shortening compared with control littermates without signs of cardiac hypertrophy. The decreased cardiac contractility was associated with a decreased performance in a treadmill experiment. In isolated cardiomyocytes, fractional shortening was significantly reduced compared with control cells. These data demonstrate that restricted deletion of Smad5 in the blood vessel wall results in viable mice. However, loss of Smad5 in cardiomyocytes leads to a mild heart