Karl L. Insogna

Lrp5 Controls Bone Formation by Inhibiting Serotonin Synthesis in the Duodenum

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 beta-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 beta-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 potential therapies to increase bone mass.

Humoral Hypercalcemia of Cancer

THE syndrome of humoral hypercalcemia of cancer was first described by Fuller Albright in 1941.1 When a patients hypercalcemia and hypophosphatemia resolved after the radiation of a single bone me...

Phosphoenolpyruvate Is a Metabolic Checkpoint of Anti-tumor T Cell Responses

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 Ca(2+)-NFAT signaling and effector functions by repressing sarco/ER Ca(2+)-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.

Cross-cultural association between dietary animal protein and hip fracture: A hypothesis

SummaryAge-adjusted female hip fracture incidence has been noted to be higher in industrialized countries than in nonindustrialized countries. A possible explanation that has received little attention is that elevated metabolic acid production associated with a high animal protein diet might lead to chronic bone buffering and bone dissolution. In an attempt to examine this hypothesis, cross-cultural variations in animal protein consumption and hip fracture incidence were examined. When female fracture rates derived from 34 published studies in 16 countries were regressed against estimates of dietary animal protein, a strong, positive association was found. This association could not plausibly be explained by either dietary calcium or total caloric intake. Recent studies suggest that the animal protein-hip fracture association could have a biologically tenable basis. We conclude that further study of the metabolic acid-osteoporosis hypothesis is warranted.

Factors associated with humoral hypercalcemia of malignancy stimulate adenylate cyclase in osteoblastic cells.

The culture media of three cell lines, a human prostate carcinoma (PC3), a rat Leydig cell tumor (Rice-500), and a rat carcinosarcoma (WRC-256), that were derived from tumors associated with humoral hypercalcemia of malignancy (HHM), were examined for stimulation of adenylate cyclase in ROS 17/2.8 osteoblastic cells and for bone resorptive activity in culture. Cells from a nonhypercalcemic variant of the WRC256 tumor served as control. Extracts from three solid human tumors, a lung adenocarcinoma from a patient with HHM and two adenocarcinoma from normocalcemic patients (lung and colon), were also examined for adenylate cyclase stimulation. We found excellent correlation between stimulation of cyclic AMP accumulation in ROS 17/2.8 cells and bone resorbing activity in culture, or production of HHM in vivo. Stimulation of adenylate cyclase by HHM factors was inhibited by the parathyroid hormone competitive inhibitor, [8norleucyl, 18norleucyl, 34tyrosinyl] bovine parathyroid hormone (3-34) amide.

Multisystem study of 20 older adults with Williams syndrome

To address the natural history of Williams syndrome (WS), we performed multisystem assessments on 20 adults with WS over 30 years of age and documented a high frequency of problems in multiple organ systems. The most striking and consistent findings were: abnormal body habitus; mild–moderate high frequency sensorineural hearing loss; cardiovascular disease and hypertension; gastrointestinal symptoms including diverticular disease; diabetes and abnormal glucose tolerance on standard oral glucose tolerance testing; subclinical hypothyroidism; decreased bone mineral density on DEXA scanning; and a high frequency of psychiatric symptoms, most notably anxiety, often requiring multimodal therapy. Review of brain MRI scans did not demonstrate consistent pathology. The adults in our cohort were not living independently and the vast majority were not competitively employed. Our preliminary findings raise concern about the occurrence of mild accelerated aging, which may additionally complicate the long‐term natural history of older adults with WS. We provide monitoring guidelines to assist in the comprehensive care of adults with WS.

Synthetic human parathyroid hormone-like protein stimulates bone resorption and causes hypercalcemia in rats.

Parathyroid hormone-like adenylate cyclase-stimulating proteins (hACSPs) have been implicated as one of the calcemic, bone-resorbing agents in patients with humoral hypercalcemia of malignancy. We report the synthesis of an amino-terminal hACSP fragment, Tyr36 hACSP (1-36) amide. The synthetic hACSP is a potent agonist of renal membrane adenylate cyclase (Km, 1.7 X 10(-10)) and of bone cell adenylate cyclase (Km 1 X 10(-9)M). It is a potent bone-resorbing agent in vitro, stimulating 45Ca release from fetal rat long bones at a concentration of 10(-9) M. When infused via osmotic minipumps into rats, it is also a potent calcemic factor in vivo, inducing a rise in serum calcium from (mean +/- SD) 10.6 +/- 0.6 to 19.7 +/- 3.2 mg/dl when infused at 1.4 micrograms/h and from 9.9 +/- 0.7 to 11.4 +/- 1.2 mg/dl when infused at 0.14 micrograms/h. These findings indicate that biologically active hACSP fragments can be synthesized. One such synthetic peptide possesses the in vitro and in vivo bioactivities demonstrated in native, tumor-derived hACSPs. It is also a potent calcemic, bone-resorbing agent.

A clinician's guide to X-linked hypophosphatemia

X‐linked hypophosphatemia (XLH) is the prototypic disorder of renal phosphate wasting, and the most common form of heritable rickets. Physicians, patients, and 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 NIH in October 2008. We briefly review the clinical and pathophysiologic features of the disorder and offer this guide in response to the conference recommendation, based on our collective accumulated experience in the management of this complex disorder.

Dietary protein, calcium metabolism, and skeletal homeostasis revisited

High dietary protein intakes are known to increase urinary calcium excretion and, if maintained, will result in sustained hypercalciuria. To date, the majority of calcium balance studies in humans have not detected an effect of dietary protein on intestinal calcium absorption or serum parathyroid hormone. Therefore, it is commonly concluded that the source of the excess urinary calcium is increased bone resorption. Recent studies from our laboratory indicate that alterations in dietary protein can, in fact, profoundly affect intestinal calcium absorption. In short-term dietary trials in healthy adults, we fixed calcium intake at 20 mmol/d while dietary protein was increased from 0.7 to 2.1 g/kg. Increasing dietary protein induced hypercalciuria in 20 women [from 3.4 +/- 0.3 ( +/- SE) during the low-protein to 5.4 +/- 0.4 mmol/d during the high-protein diet]. The increased dietary protein was accompanied by a significant increase in intestinal calcium absorption from 18.4 +/- 1.3% to 26.3 +/- 1.5% (as determined by dual stable isotopic methodology). Dietary protein intakes at and below 0.8 g/kg were associated with a probable reduction in intestinal calcium absorption sufficient to cause secondary hyperparathyroidism. The long-term consequences of these low-protein diet-induced changes in mineral metabolism are not known, but the diet could be detrimental to skeletal health. Of concern are several recent epidemiologic studies that demonstrate reduced bone density and increased rates of bone loss in individuals habitually consuming low-protein diets. Studies are needed to determine whether low protein intakes directly affect rates of bone resorption, bone formation, or both.

LATS1 tumour suppressor affects cytokinesis by inhibiting LIMK1

LATS (large tumour suppressor) is a family of conserved tumour suppressors identified in Drosophila and mammals. Here we show that human LATS1 binds to LIMK1 in vitro and in vivo and colocalizes with LIMK1 at the actomyosin contractile ring during cytokinesis. LATS1 inhibits both the phosphorylation of cofilin by LIMK1 and LIMK1-induced cytokinesis defects. Inactivation of LATS1 by antibody microinjection or RNA-mediated interference in cells, or gene knockout in mice, abrogates cytokinesis and increases the percentage of multinucleate cells. Our findings indicate that LATS1 is a novel cytoskeleton regulator that affects cytokinesis by regulating actin polymerization through negative modulation of LIMK1.