PPARδ modulation rescues mitochondrial fatty acid oxidation defects in the mdx model of muscular dystrophy.

Duchenne muscular dystrophy (DMD) is a recessive, fatal X-linked disease that is characterized by progressive skeletal muscle wasting due to the absence of dystrophin, which is an a essential protein that bridges the inner cytoskeleton and extra-cellular matrix. This study set out to characterize the mitochondria in primary muscle satellite cell derived myoblasts from mdx mice and wild type control mice. Compared to wild type derived cells the mdx derived cells have reduced mitochondrial bioenergetics and have fewer mitochondria. Here, we demonstrate that a novel PPARδ modulator improves mitochondrial function in the mdx mice, which supports that modulating PPARδ may be therapeutically beneficial in DMD patients.

Discovery of Orally Bioavailable and Liver-Targeted Hypoxia-Inducible Factor Prolyl Hydroxylase (HIF-PHD) Inhibitors for the Treatment of Anemia.

We report herein the design and synthesis of a series of orally active, liver-targeted hypoxia-inducible factor prolyl hydroxylase (HIF-PHD) inhibitors for the treatment of anemia. In order to mitigate the concerns for potential systemic side effects, we pursued liver-targeted HIF-PHD inhibitors relying on uptake via organic anion transporting polypeptides (OATPs). Starting from a systemic HIF-PHD inhibitor (1), medicinal chemistry efforts directed toward reducing permeability and, at the same time, maintaining oral absorption led to the synthesis of an array of structurally diverse hydroxypyridone analogues. Compound 28a was chosen for further profiling, because of its excellent in vitro profile and liver selectivity. This compound significantly increased hemoglobin levels in rats, following chronic QD oral administration, and displayed selectivity over systemic effects.

Discovery of N-[Bis(4-methoxyphenyl)methyl]-4-hydroxy-2-(pyridazin-3-yl)pyrimidine-5-carboxamide (MK-8617), an Orally Active Pan-Inhibitor of Hypoxia-Inducible Factor Prolyl Hydroxylase 1-3 (HIF PHD1-3) for the Treatment of Anemia.

The discovery of novel 4-hydroxy-2-(heterocyclic)pyrimidine-5-carboxamide inhibitors of hypoxia-inducible factor (HIF) prolyl hydroxylases (PHD) is described. These are potent, selective, orally bioavailable across several species, and active in stimulating erythropoiesis. Mouse and rat studies showed hematological changes with elevations of plasma EPO and circulating reticulocytes following single oral dose administration, while 4-week q.d. po administration in rat elevated hemoglobin levels. A major focus of the optimization process was to decrease the long half-life observed in higher species with early compounds. These efforts led to the identification of 28 (MK-8617), which has advanced to human clinical trials for anemia.

A single dose of EGLN1 siRNA yields increased erythropoiesis in nonhuman primates.

Decreased production of erythropoietin (EPO) causes anemia in patients with chronic kidney disease, and recombinant human EPO is used to treat renal failure associated anemia. The liver, the main EPO-producing organ in utero, maintains the capacity to produce EPO in the adult but in insufficient quantities to restore hemoglobin levels to normal in patients with impaired renal function. Inhibition of prolyl-4-hydroxylase domain (PHD) proteins is known to cause an increase in EPO production through its effects on hypoxia inducible factor. Here, we utilized small interfering RNA (siRNA) targeting EGLN1, the gene encoding the PHD2 protein, to investigate the phenotypic consequences in nonhuman primates. A single, well-tolerated intravenous dose of an optimized EGLN1 siRNA encapsulated in a lipid nanoparticle formulation caused robust mRNA silencing in the liver, leading to increases in serum EPO and hemoglobin. The siRNA-induced erythropoiesis was dose-dependent and was sustained for at least 2 months. These data point to the potential for an RNA interference-based, liver-targeted therapeutic approach for the treatment of anemia.

Epidermal development and wound healing in matrix metalloproteinase 13-deficient mice.

Degradation of the extracellular matrix, which is an indispensable step in tissue remodelling processes such as embryonic development and wound healing of the skin, has been attributed to collagenolytic activity of members of the matrix metalloproteinase family (MMPs). Here, we employed mmp13 knockout mice to elucidate the function of MMP13 in embryonic skin development, skin homeostasis, and cutaneous wound healing. Overall epidermal architecture and dermal composition of non-injured skin were indistinguishable from wild-type mice. Despite robust expression of MMP13 in the early phase of wound healing, wild-type and mmp13 knockout animals did not differ in their efficiency of re-epithelialization, inflammatory response, granulation tissue formation, angiogenesis, and restoration of basement membrane. Yet, among other MMPs also expressed during wound healing, MMP8 was found to be enhanced in wounds of MMP13-deficient mice. In summary, skin homeostasis and also tissue remodelling processes like embryonic skin development and cutaneous wound healing are independent of MMP13 either owing to MMP13 dispensability or owing to functional substitution by other collagenolytic proteinases such as MMP8.

Mice deficient in Ext2 lack heparan sulfate and develop exostoses.

Hereditary multiple exostoses (HME) is a genetically heterogeneous human disease characterized by the development of bony outgrowths near the ends of long bones. HME results from mutations in EXT1 and EXT2, genes that encode glycosyltransferases that synthesize heparan sulfate chains. To study the relationship of the disease to mutations in these genes, we generated Ext2-null mice by gene targeting. Homozygous mutant embryos developed normally until embryonic day 6.0, when they became growth arrested and failed to gastrulate, pointing to the early essential role for heparan sulfate in developing embryos. Heterozygotes had a normal lifespan and were fertile; however, analysis of their skeletons showed that about one-third of the animals formed one or more ectopic bone growths (exostoses). Significantly, all of the mice showed multiple abnormalities in cartilage differentiation, including disorganization of chondrocytes in long bones and premature hypertrophy in costochondral cartilage. These changes were not attributable to a defect in hedgehog signaling, suggesting that they arise from deficiencies in other heparan sulfate-dependent pathways. The finding that haploinsufficiency triggers abnormal cartilage differentiation gives insight into the complex molecular mechanisms underlying the development of exostoses.

Altered endochondral bone development in matrix metalloproteinase 13-deficient mice.

The assembly and degradation of extracellular matrix (ECM) molecules are crucial processes during bone development. In this study, we show that ECM remodeling is a critical rate-limiting step in endochondral bone formation. Matrix metalloproteinase (MMP) 13 (collagenase 3) is poised to play a crucial role in bone formation and remodeling because of its expression both in terminal hypertrophic chondrocytes in the growth plate and in osteoblasts. Moreover, a mutation in the human MMP13 gene causes the Missouri variant of spondyloepimetaphyseal dysplasia. Inactivation of Mmp13 in mice through homologous recombination led to abnormal skeletal growth plate development. Chondrocytes differentiated normally but their exit from the growth plate was delayed. The severity of the Mmp13- null growth plate phenotype increased until about 5 weeks and completely resolved by 12 weeks of age. Mmp13-null mice had increased trabecular bone, which persisted for months. Conditional inactivation of Mmp13 in chondrocytes and osteoblasts showed that increases in trabecular bone occur independently of the improper cartilage ECM degradation caused by Mmp13 deficiency in late hypertrophic chondrocytes. Our studies identified the two major components of the cartilage ECM, collagen type II and aggrecan, as in vivo substrates for MMP13. We found that degradation of cartilage collagen and aggrecan is a coordinated process in which MMP13 works synergistically with MMP9. Mice lacking both MMP13 and MMP9 had severely impaired endochondral bone, characterized by diminished ECM remodeling, prolonged chondrocyte survival, delayed vascular recruitment and defective trabecular bone formation (resulting in drastically shortened bones). These data support the hypothesis that proper ECM remodeling is the dominant rate-limiting process for programmed cell death, angiogenesis and osteoblast recruitment during normal skeletal morphogenesis.

How proteases regulate bone morphogenesis.

Matrix metalloproteinases (MMPs) degrade most components of the extracellular matrix (ECM), as well as many non-ECM molecules. MMPs participate in (1). degradation of ECM to allow cell migration; (2). alteration of the ECM microenvironment resulting in alteration in cellular behavior; (3). modulation of biologically active molecules by direct cleavage or release from ECM stores; (4). regulation of the activity of other proteases; and (5). cell attachment, proliferation, differentiation, and apoptosis. We have sought to understand the role of MMPs during development and tissue repair in transgenic mice. Endochondral bone formation presents a particularly interesting developmental challenge. During this process, an avascular tissue (cartilage) is converted into one of the most highly vascularized tissues (bone) in the vertebrate body. Ossification begins with invasion of the calcified hypertrophic cartilage by capillaries. Apoptosis of the terminal hypertrophic chondrocytes, degradation of the cartilage matrix, and deposition of bone matrix by osteoblasts accompanies neovascularization of the growth plate. Remodeling of ECM results in a cavity filled with vascular channels containing hematopoietic cells. Our results reveal that MMP9, MMP13, and vascular endothelial growth factor are key regulators for the remodeling of the skeletal tissues. They coordinate not only matrix degradation, but also the recruitment and differentiation of endothelial cells, osteoclasts, chondroclasts, and osteoprogenitors.