The LRP5V171 mutation causes high bone density, with a thickened mandible and torus palatinus, by impairing the action of a normal antagonist of the Wnt pathway and thus increasing Wnt signaling. These findings demonstrate the role of altered LRP5 function in high bone mass and point to Dkk as a potential target for the prevention or treatment of osteoporosis.

SUMMARY Activated T cells engage aerobic glycolysis and anabolic metabolism for growth, proliferation, and effector functions. We propose that a glucose-poor tumor microenvironment limits aerobic glycolysis in tumor-infiltrating T cells, which suppresses tumoricidal effector functions. We discovered a new role for the glycolytic metabolite phosphoenolpyruvate (PEP) in sustaining T cell receptor-mediated Ca2+-NFAT signaling and effector functions by repressing sarco/ER Ca2+-ATPase (SERCA) activity. Tumor-specific CD4 and CD8 T cells could be metabolically reprogrammed by increasing PEP production through overexpression of phosphoenolpyruvate carboxykinase 1 (PCK1), which bolstered effector functions. Moreover, PCK1-overexpressing T cells restricted tumor growth and prolonged the survival of melanoma-bearing mice. This study uncovers new metabolic checkpoints for T cell activity and demonstrates that metabolic reprogramming of tumor-reactive T cells can enhance anti-tumor T cell responses, illuminating new forms of immunotherapy.

Loss- and gain-of-function mutations in the broadly expressed gene Lrp5 affect bone formation causing osteoporosis and high bone mass, respectively. Although Lrp5 is viewed as a Wnt coreceptor osteoblast-specific disruption of β-Catenin does not affect bone formation. Instead, we show here that Lrp5 inhibits expression of Tph1, the rate-limiting biosynthetic enzyme for serotonin in enterochromaffin cells of the duodenum. Accordingly, decreasing serotonin blood levels normalizes bone formation and bone mass in Lrp5-deficient mice and gut- but not osteoblast-specific Lrp5 inactivation decreases bone formation in a β-Catenin–independent manner. Moreover, gut-specific activation of Lrp5, or inactivation of Tph1, increases bone mass and prevents ovariectomy-induced bone loss. Serotonin acts on osteoblasts through the Htr1b receptor and CREB to inhibit their proliferation. By identifying duodenum-derived serotonin as a hormone inhibiting bone formation in an Lrp5-dependent manner this study broadens our understanding of bone remodeling and suggests novel therapies to increase bone mass.

X-linked hypophosphatemia (XLH) is the prototypic disorder of renal phosphate wasting, and the most common form of heritable rickets. Physicians, patients, and XLH support groups have all expressed concerns about the dearth of information about this disease and the lack of treatment guidelines which frequently lead to missed diagnoses or mismanagement. This perspective addresses the recommendation by conferees for the dissemination of concise and accessible treatment guidelines for clinicians arising from the “Advances in Rare Bone Diseases Scientific Conference,” held at the National Institutes of Health in October 2008. We briefly review the clinical and pathophysiologic features of the disorder, and offer this guide in response to the conference recommendation, base on our collective accumulated experience in the management of this complex disorder.

Background. X-linked hypophosphatemia (XLH) is Funding. Kyowa Hakko Kirin Pharma, Inc.Introduction X-linked hypophosphatemia (XLH), the most common heritable form of rickets or osteomalacia, occurs due to loss-of-function mutations in PHEX, which result in elevated blood levels of fibroblast growth factor 23 (FGF23) (1, 2). FGF23 decreases renal tubular reabsorption of phosphate by reducing the abundance and possibly the activity of sodium-phosphate cotransporters on the apical membrane of proximal tubular epithelium, thereby reducing serum phosphate (measured as inorganic phosphorus, Pi) concentrations (3-5). Elevated FGF23 also decreases renal 1-α-hydroxylase activity, leading to low or inappropriately normal blood levels of 1,25-dihydroxyvitamin D [1,25(OH) 2 D] (1, 2).