Maternal Smoking and Congenital Heart Defects, National Birth Defects Prevention Study, 1997-2011.

OBJECTIVES: To assess associations between maternal smoking and congenital heart defects (CHDs) in offspring. STUDY DESIGN: We performed a retrospective case-control study using data for cases of CHD (n = 8339) and nonmalformed controls (n = 11 020) from all years (1997-2011) of the National Birth Defects Prevention Study. Maternal self-reported smoking 1 month before through 3 months after conception was evaluated as a binary (none, any) and categorical (light, medium, heavy) exposure. Multivariable logistic regression was used to estimate aOR and 95% CIs. Stratified analyses were performed for septal defects according to maternal age, prepregnancy body mass index, and maternal race/ethnicity. RESULTS: Multiple CHDs displayed modest associations with any level of maternal periconceptional smoking independent of potential confounders; the strongest associations were for aggregated septal defects (OR, 1.5; 95% CI, 1.3-1.7), tricuspid atresia (OR, 1.7; 95% CI, 1.0-2.7), and double outlet right ventricle (DORV) (OR, 1.5; 95% CI, 1.1-2.1). Tricuspid atresia and DORV also displayed dose-response relationships. Among heavy smokers, the highest odds were again observed for tricuspid atresia (aOR 3.0; 95% CI, 1.5-6.1) and DORV (aOR 1.5; 95% CI, 1.1-2.2). Heavy smokers ≥35 years old more frequently had a child with a septal defect when compared with similarly aged nonsmokers (aOR 2.3; 95% CI, 1.4-3.9). CONCLUSIONS: Maternal periconceptional smoking is most strongly associated with septal defects, tricuspid atresia, and DORV; the risk for septal defects is modified by maternal age.

FOXOs attenuate bone formation by suppressing Wnt signaling.

Wnt/ß-catenin/TCF signaling stimulates bone formation and suppresses adipogenesis. The hallmarks of skeletal involution with age, on the other hand, are decreased bone formation and increased bone marrow adiposity. These changes are associated with increased oxidative stress and decreased growth factor production, which activate members of the FOXO family of transcription factors. FOXOs in turn attenuate Wnt/ß-catenin signaling by diverting ß-catenin from TCF- to FOXO-mediated transcription. We show herein that mice lacking Foxo1, -3, and -4 in bipotential progenitors of osteoblast and adipocytes (expressing Osterix1) exhibited increased osteoblast number and high bone mass that was maintained in old age as well as decreased adiposity in the aged bone marrow. The increased bone mass in the Foxo-deficient mice was accounted for by increased proliferation of osteoprogenitor cells and bone formation resulting from upregulation of Wnt/ß-catenin signaling and cyclin D1 expression, but not changes in redox balance. Consistent with this mechanism, ß-catenin deletion in Foxo null cells abrogated both the increased cyclin D1 expression and proliferation. The elucidation of a restraining effect of FOXOs on Wnt signaling in bipotential progenitors suggests that FOXO activation by accumulation of age-associated cellular stressors may be a seminal pathogenetic mechanism in the development of involutional osteoporosis.

Non-nuclear-initiated actions of the estrogen receptor protect cortical bone mass.

Extensive evidence has suggested that at least some of the effects of estrogens on bone are mediated via extranuclear estrogen receptor α signaling. However, definitive proof for this contention and the extent to which such effects may contribute to the overall protective effects of estrogens on bone maintenance have remained elusive. Here, we investigated the ability of a 17ß-estradiol (E2) dendrimer conjugate (EDC), incapable of stimulating nuclear-initiated actions of estrogen receptor α, to prevent the effects of ovariectomy (OVX) on the murine skeleton. We report that EDC was as potent as an equimolar dose of E2 in preventing bone loss in the cortical compartment that represents 80% of the entire skeleton, but was ineffective on cancellous bone. In contrast, E2 was effective in both compartments. Consistent with its effect on cortical bone mass, EDC partially prevented the loss of both vertebral and femoral strength. In addition, EDC, as did E2, prevented the OVX-induced increase in osteoclastogenesis, osteoblastogenesis, and oxidative stress. Nonetheless, the OVX-induced decrease in uterine weight was unaltered by EDC but was restored by E2. These results demonstrate that the protection of cortical bone mass by estrogens is mediated, at least in part, via a mechanism that is distinct from the classic mechanism of estrogen action on reproductive organs.

Changes in activities of daily living, nutrient intake, and systemic inflammation in elderly adults receiving recuperative care.

OBJECTIVES: To determine the relationships between physical function, systemic inflammation, and nutrient intake in elderly adults who are deconditioned or recovering from medical illness. DESIGN: Prospective observational study. SETTING: Recuperative care and rehabilitation setting of a Veterans Affairs hospital. PARTICIPANTS: Older adults assessed to be in need of and likely to benefit from specialized inpatient care (N = 336, aged 78.9 ± 7.5, median length of stay 24 days). MEASUREMENTS: Functional assessments and plasma analyses for albumins and inflammatory markers were performed at admission and discharge. Complete nutrient intake assessments were performed daily. Katz (independence in activities of daily living) and walking endurance (distance capability and summation of need for assistive device and human help) scores were based on direct observation and provider query. Data were analyzed using least-squares and logistic regression analyses. RESULTS: Changes in physical function between admission and discharge were positively correlated with change in nutrient intake and inversely correlated with inflammation at admission and its change. Participants in the upper quartile of change for nutrient intake (particularly improved protein intake) were two to three times as likely to experience a clinically significant change in functional status during the hospitalization. Similarly, the odds of experiencing an improvement in physical function were two to four times as great for participants whose C-reactive protein levels declined as for those whose levels increased. These relationships remained significant after controlling for age, length of stay, and other baseline indicators of health status. CONCLUSION: Protein intake and inflammation are significantly correlated with functional recovery for aging individuals undergoing recuperative care and rehabilitation. Future studies should investigate whether combined interventions that target these factors improve recovery during hospitalization for this population.

Osteoprotegerin prevents glucocorticoid-induced osteocyte apoptosis in mice.

The adverse skeletal effects of glucocorticoid excess are due to increased osteoclast survival, decreased production of osteoblasts, and increased apoptosis of osteoblasts and osteocytes, but it remains unknown which of these is the principle cause of the decrease in bone strength. Previous studies suggested that osteocytes contribute to bone strength independently of changes in bone mass. Administration of the receptor activator for nuclear factor κB ligand (RANKL) antagonist osteoprotegerin (OPG) rapidly decreases osteoclasts followed by a decrease in osteoblasts but should not affect the long-lived osteocytes. Therefore, to distinguish between glucocorticoid effects on osteoclasts, osteoblasts, or osteocytes, we administered glucocorticoids, alone or in combination with OPG with the fragment crystallizable region of Ig heavy chains (OPG-Fc), to mice. The suppressive effect of glucocorticoids on spinal bone mineral density, cortical thickness, and strength was prevented by OPG-Fc. OPG-Fc, with or without glucocorticoids, profoundly reduced osteoclasts, osteoblasts, and bone formation. Unexpectedly, OPG-Fc prevented the glucocorticoid-induced increase in osteocyte apoptosis and reduction in solute transport from the systemic circulation to the osteocyte-lacunar-canalicular network. The fluid in the osteocyte-lacunar-canalicular network was inversely related to osteocyte apoptosis and directly related to bone mineral density. Consistent with the in vivo findings, Both OPG-Fc and OPG decreased glucocorticoid-induced apoptosis of MLO-Y4 osteocytic cells. OPG can also bind and antagonizes the activity of the TNF-related apoptosis-inducing ligand (TRAIL), but glucocorticoids did not change TRAIL expression, and knockdown of TRAIL did not prevent OPG-Fc from reducing glucocorticoid-induced osteocyte apoptosis. Based on these results, we conclude that at least part of the OPG-induced preservation of bone strength is due to the maintenance of osteocyte viability and the lacunar-canalicular network.

Preoperative sclerotherapy of facial venous malformations: impact on surgical parameters and long-term follow-up.

PURPOSE: To analyze the operative benefit of preoperative sclerotherapy of facial venous malformations and assess long-term patient outcome. MATERIALS AND METHODS: Preoperative sclerotherapy was performed in 24 consecutive patients referred before resection of facial venous malformation. Pretreatment imaging was reviewed for malformation dimensions (length, width, and height), and volumes were estimated. Sclerotherapy was performed with 3% sodium tetradecyl in the first 15 patients and 98% dehydrated alcohol in the remaining 9 patients. Operative blood loss, operative time, transfusion requirement, and hospital stay were recorded. Operative time per lesion volume and operative blood loss per lesion volume were calculated. Results were compared with 15 historical control patients who underwent resection of facial venous malformations without preoperative sclerotherapy. Long-term follow-up of study and control patients was performed. RESULTS: Compared with controls, patients undergoing preoperative venous sclerotherapy were significantly older (P = .0206) and had larger lesions in all three dimensions (height, P = .0002; length, P = .0010; width, P = .0004). Patients receiving sclerotherapy had shorter operative time per lesion volume (P < .0001) and reduced blood loss per lesion volume (P < .0001). Neither hospital stay nor the need for blood transfusion differed from the control patients (P = .2449 and P = .6857). Mild periprocedural complications were encountered in 12.5% of cases, and nerve paresis occurred in 8.3% of cases. Long-term follow-up revealed retreatment was required in 2 of 24 patients (8.3%). CONCLUSIONS: Preoperative sclerotherapy of venous malformations was associated with less operative time per lesion volume and less operative blood loss per lesion volume. Long-term follow-up revealed a low need for retreatment.

Decreased oxidative stress and greater bone anabolism in the aged, when compared to the young, murine skeleton with parathyroid hormone administration.

Because of recent insights into the pathogenesis of age-related bone loss, we investigated whether intermittent parathyroid hormone (PTH) administration antagonizes the molecular mechanisms of the adverse effects of aging on bone. Parathyroid hormone produced a greater increase in vertebral trabecular bone mineral density and bone volume as well as a greater expansion of the endocortical bone surface in the femur of 26- when compared to 6 -month-old female C57BL/6 mice. Moreover, PTH increased trabecular connectivity in vertebrae, and the toughness of both vertebrae and femora in old, but not young, mice. Parathyroid hormone also increased the rate of bone formation and reduced osteoblast apoptosis to a greater extent in the old mice. Most strikingly, PTH reduced reactive oxygen species, p66(Shc) phosphorylation, and expression of the lipoxygenase Alox15, and it increased glutathione and stimulated Wnt signaling in bone of old mice. Parathyroid hormone also antagonized the effects of oxidative stress on p66(Shc) phosphorylation, Forkhead Box O transcriptional activity, osteoblast apoptosis, and Wnt signaling in vitro. In contrast, administration of the antioxidants N-acetyl cysteine or pegylated catalase reduced osteoblast progenitors and attenuated proliferation and Wnt signaling. These results suggest that PTH has a greater bone anabolic efficacy in old age because in addition to its other positive actions on bone formation, it antagonizes the age-associated increase in oxidative stress and its adverse effects on the birth and survival of osteoblasts. On the other hand, ordinary antioxidants cannot restore bone mass in old age because they slow remodeling and attenuate osteoblastogenesis by interfering with Wnt signaling.

Endogenous glucocorticoids decrease skeletal angiogenesis, vascularity, hydration, and strength in aged mice.

Aging or glucocorticoid excess decrease bone strength more than bone mass in humans and mice, but an explanation for this mismatch remains elusive. We report that aging in C57BL/6 mice was associated with an increase in adrenal production of glucocorticoids as well as bone expression of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 1, the enzyme that activates glucocorticoids. Aging also decreased the volume of the bone vasculature and solute transport from the peripheral circulation to the lacunar-canalicular system. The same changes were reproduced by pharmacologic hyperglucocorticoidism. Furthermore, mice in which osteoblasts and osteocytes were shielded from glucocorticoids via cell-specific transgenic expression of 11beta-HSD type 2, the enzyme that inactivates glucocorticoids, were protected from the adverse effects of aging on osteoblast and osteocyte apoptosis, bone formation rate and microarchitecture, crystallinity, vasculature volume, interstitial fluid, and strength. In addition, glucocorticoids suppressed angiogenesis in fetal metatarsals and hypoxia inducible factor-1alpha transcription and vascular endothelial growth factor production in osteoblasts and osteocytes. These results, together with the evidence that dehydration of bone decreases strength, reveal that endogenous glucocorticoids increase skeletal fragility in old age as a result of cell autonomous effects on osteoblasts and osteocytes leading to interconnected decrements in bone angiogenesis, vasculature volume, and osteocyte-lacunar-canalicular fluid.

The false discovery rate: a key concept in large-scale genetic studies.

BACKGROUND: In experimental research, a statistical test is often used for making decisions on a null hypothesis such as that the means of gene expression in the normal and tumor groups are equal. Typically, a test statistic and its corresponding P value are calculated to measure the extent of the difference between the two groups. The null hypothesis is rejected and a discovery is declared when the P value is less than a prespecified significance level. When more than one test is conducted, use of a significance level intended for use by a single test typically leads to a large chance of false-positive findings. METHODS: This paper presents an overview of the multiple testing framework and describes the false discovery rate (FDR) approach to determining the significance cutoff when a large number of tests are conducted. RESULTS: The FDR is the expected proportion of the null hypotheses that are falsely rejected divided by the total number of rejections. An FDR-controlling procedure is described and illustrated with a numerical example. CONCLUSIONS: In multiple testing, a classical "family-wise error rate" (FWE) approach is commonly used when the number of tests is small. When a study involves a large number of tests, the FDR error measure is a more useful approach to determining a significance cutoff, as the FWE approach is too stringent. The FDR approach allows more claims of significant differences to be made, provided the investigator is willing to accept a small fraction of false-positive findings.

Estrogens attenuate oxidative stress and the differentiation and apoptosis of osteoblasts by DNA-binding-independent actions of the ERalpha.

Estrogens diminish oxidative stress in bone and bone marrow, attenuate the generation of osteoblasts, and decrease the prevalence of mature osteoblast apoptosis. We have searched for the molecular mechanism of these effects using as tools a mouse model bearing an estrogen receptor alpha (ERalpha) knock-in mutation that prevents binding to DNA (ERalpha(NERKI/-)) and several osteoblast progenitor cell models expressing the wild-type ERalpha or the ERalpha(NERKI/-). We report that the ability of estrogens to diminish the generation of reactive oxygen species, stimulate the activity of glutathione reductase, and decrease the phosphorylation of p66(shc), as well as osteoblastogenesis and osteoblast number and apoptosis, were fully preserved in ERalpha(NERKI/-) mice, indicating that the DNA-binding function of the ERalpha is dispensable for all these effects. Consistent with the attenuation of osteoblastogenesis in this animal model, 17beta-estradiol attenuated bone morphogenetic protein 2 (BMP-2)-induced gene transcription and osteoblast commitment and differentiation in murine and human osteoblastic cell lines. Moreover, 17beta-estradiol attenuated BMP-2-induced differentiation of primary cultures of calvaria- or bone marrow-derived osteoblastic cells from ERalpha(NERKI/-) mice as effectively as in cells from wild-type littermates. The inhibitory effect of the hormone on BMP-2 signaling resulted from an ERalpha-mediated activation of ERKs and the phosphorylation of Smad1 at the linker region of the protein, which leads to proteasomal degradation. These results illustrate that the effects of estrogens on oxidative stress and the birth and death of osteoblasts do not require the binding of ERalpha to DNA response elements, but instead they result from the activation of cytoplasmic kinases.

Giant osteoclast formation and long-term oral bisphosphonate therapy.

BACKGROUND: Bisphosphonates decrease bone resorption and are commonly used to treat or prevent osteoporosis. However, the effect of bisphosphonates on their target cells remains enigmatic, since in patients benefiting from therapy, little change, if any, has been observed in the number of osteoclasts, which are the cells responsible for bone resorption. METHODS: We examined 51 bone-biopsy specimens obtained after a 3-year, double-blind, randomized, placebo-controlled, dose-ranging trial of oral alendronate to prevent bone resorption among healthy postmenopausal women 40 through 59 years of age. The patients were assigned to one of five groups: those receiving placebo for 3 years; alendronate at a dose of 1, 5, or 10 mg per day for 3 years; or alendronate at a dose of 20 mg per day for 2 years, followed by placebo for 1 year. Formalin-fixed, undecalcified planar sections were assessed by bone histomorphometric methods. RESULTS: The number of osteoclasts was increased by a factor of 2.6 in patients receiving 10 mg of alendronate per day for 3 years as compared with the placebo group (P<0.01). Moreover, the number of osteoclasts increased as the cumulative dose of the drug increased (r=0.50, P<0.001). Twenty-seven percent of these osteoclasts were giant cells with pyknotic nuclei that were adjacent to superficial resorption cavities. Furthermore, giant, hypernucleated, detached osteoclasts with 20 to 40 nuclei were found after alendronate treatment had been discontinued for 1 year. Of these large cells, 20 to 37% were apoptotic, according to both their morphologic features and positive findings from in situ end labeling. CONCLUSIONS: Long-term alendronate treatment is associated with an increase in the number of osteoclasts, which include distinctive giant, hypernucleated, detached osteoclasts that are undergoing protracted apoptosis.

Changes in prealbumin, nutrient intake, and systemic inflammation in elderly recuperative care patients.

OBJECTIVES: To determine the relationship between prealbumin, nutrient intake, and indicators of inflammation for recuperative and rehabilitative care patients. DESIGN: Prospective cohort. SETTING: Recuperative Care Unit within a Veterans Administration Nursing Home Care Unit. PARTICIPANTS: One hundred eleven men (100 white; mean age 80, range 64-93). MEASUREMENTS: Prealbumin and seven markers of inflammation (C-reactive protein (CRP), tumor necrosis factor, and interleukin-6 (IL-6) and their soluble receptors) were measured at admission and discharge (median length of stay 23 days, interquartile range 15-40 days). Detailed calorie counts were performed daily, and intake was expressed as a percentage of estimated requirements for protein (1.5 g/kg body weight per day) and energy (Harris-Benedict equation). The study objective was examined using least-squares regression analysis. RESULTS: Discharge prealbumin and the change in prealbumin were positively correlated with protein and energy intake and inversely correlated with markers of inflammation, particularly CRP and IL-6. When all covariates were included in a multivariable regression analysis, the markers of inflammation predominantly accounted for the variance in prealbumin change (56%), whereas discharge protein intake accounted for 6%. CONCLUSION: For older recuperative care patients, prealbumin and its change during hospitalization are positively associated with protein intake, but inflammation or changes in inflammation appear to exert a much more-powerful influence on prealbumin concentration. Given the potential confounding effects of inflammation, monitoring the change in prealbumin is not an adequate substitute for a more-detailed nutritional assessment in this population.

Skeletal involution by age-associated oxidative stress and its acceleration by loss of sex steroids.

Both aging and loss of sex steroids have adverse effects on skeletal homeostasis, but whether and how they may influence each others negative impact on bone remains unknown. We report herein that both female and male C57BL/6 mice progressively lost strength (as determined by load-to-failure measurements) and bone mineral density in the spine and femur between the ages of 4 and 31 months. These changes were temporally associated with decreased rate of remodeling as evidenced by decreased osteoblast and osteoclast numbers and decreased bone formation rate; as well as increased osteoblast and osteocyte apoptosis, increased reactive oxygen species levels, and decreased glutathione reductase activity and a corresponding increase in the phosphorylation of p53 and p66(shc), two key components of a signaling cascade that are activated by reactive oxygen species and influences apoptosis and lifespan. Exactly the same changes in oxidative stress were acutely reproduced by gonadectomy in 5-month-old females or males and reversed by estrogens or androgens in vivo as well as in vitro. We conclude that the oxidative stress that underlies physiologic organismal aging in mice may be a pivotal pathogenetic mechanism of the age-related bone loss and strength. Loss of estrogens or androgens accelerates the effects of aging on bone by decreasing defense against oxidative stress.

Hypoalbuminemia 3 months after hospital discharge: significance for long-term survival.

OBJECTIVES: To determine change in albumin from hospital discharge to 3-month follow-up and the prognostic significance of persistent hypoalbuminemia in older veteran patients. DESIGN: A prospective cohort study. SETTING: A geriatric rehabilitation unit of a university-affiliated Department of Veterans Affairs hospital. PARTICIPANTS: The study population consisted of 282 subjects (of 322 randomly selected discharges who were free of cancer and terminal conditions) that completed the 90-day postdischarge assessment; most were older (75.4+/-8.6), white (76%), and male (99%). MEASUREMENTS: Each subject completed a comprehensive discharge assessment, had a repeat albumin an average of 94 days later, and was then tracked for 5 years. The strongest predictors of survival were identified using Cox proportional hazards regression analysis. RESULTS: Between hospital discharge and the 3-month reassessment, albumins improved by more than 2 g/L in 122 subjects (43%), stayed the same in 112 subjects (40%), and deteriorated by more than 2 g/L in the rest. During follow-up, 190 subjects (67%) died. Of the 38 nutritional, functional, demographic, and illness severity variables evaluated, the 3-month postdischarge albumin was the strongest predictor of long-term mortality. Those with albumins less than 35 g/L had a 2.6 times greater mortality than those with albumins of 40 g/L or greater (relative risk=2.6, 95% confidence interval=1.8-3.8). After controlling for 3-month albumin, hospital-discharge albumin was not significantly associated with long-term mortality. CONCLUSION: In older people, a low serum albumin 3 months after hospital discharge is associated with a poor long-term prognosis. It is not known whether this represents ongoing inflammation or inadequate nutrition.

Intralesional immunotherapy of warts with mumps, Candida, and Trichophyton skin test antigens: a single-blinded, randomized, and controlled trial.

BACKGROUND: Warts occur commonly in humans. Destructive modalities are generally the first physician-administered therapy. Other treatment options include immunotherapy. Intralesional immunotherapy using mumps, Candida, or Trichophyton skin test antigens has proved efficacy in the treatment of warts. OBJECTIVES: To determine rates of wart resolution in response to injection of antigen alone, antigen plus interferon alfa-2b, interferon alfa-2b alone, and normal saline; and to compare response according to viral type, major histocompatibility complex antigens, and peripheral blood mononuclear cell proliferation to autologous human papillomavirus antigen before and after injection. DESIGN: Randomized, single-blinded, placebo-controlled, clinical trial. SETTING: Medical school-based dermatology department. PATIENTS: Two hundred thirty-three patients clinically diagnosed as having 1 or more warts. Main Outcome Measure Clinical resolution of warts in response to intralesional immunotherapy. RESULTS: Responders were observed in all treatment arms, but were significantly more likely to have received antigen (P<.001). Resolution of distant untreated warts was observed, and was significantly more likely in subjects receiving antigen (P<.001). Interferon did not significantly enhance the response rate (P = .20) and did not differ from normal saline (P = .65). No viral type or major histocompatibility complex antigen correlated with response or lack of response (P>.99 and P = .86, respectively). A positive peripheral blood mononuclear cell proliferation assay result (2 times pretreatment levels) was significantly more likely among responders (P = .002). While there was no significant difference in response based on sex (P = .56), older subjects (>40 years) were less likely to respond (P = .01). CONCLUSIONS: Intralesional immunotherapy using injection of Candida, mumps, or Trichophyton skin test antigens is an effective treatment for warts, as indicated by significantly higher response rates and distant response rates in subjects receiving antigen. Viral type and major histocompatibility complex antigens did not seem to influence treatment response. Response is accompanied by proliferation of peripheral blood mononuclear cells to human papillomavirus antigens, suggesting that a human papillomavirus-directed cell-mediated immune response plays a role in wart resolution.

Proteasomal degradation of Runx2 shortens parathyroid hormone-induced anti-apoptotic signaling in osteoblasts. A putative explanation for why intermittent administration is needed for bone anabolism.

It is unknown why sustained elevation of parathyroid hormone (PTH) stimulates bone resorption, whereas intermittent administration stimulates bone formation. We show in mice that daily injections of PTH attenuate osteoblast apoptosis, thereby increasing osteoblast number, bone formation rate, and bone mass, but do not affect osteoclast number. In contrast, sustained elevation of PTH, achieved either by infusion or by raising endogenous hormone secretion with a calcium-deficient diet, does not affect osteoblast apoptosis but increases osteoclast number. Attenuation of apoptosis by PTH in cultured osteoblastic cells requires protein kinase A-mediated phosphorylation and inactivation of the pro-apoptotic protein Bad as well as transcription of survival genes, like Bcl-2, mediated by CREB (cAMP response element-binding protein) and Runx2. But, PTH also increases proteasomal proteolysis of Runx2. Moreover, the anti-apoptotic effect of PTH is prolonged by inhibition of proteasomal activity, by overexpressing a dominant negative form of the E3 ligase (ubiquitin-protein isopeptide ligase) that targets Runx2 for degradation (Smurf1), or by overexpressing Runx2 itself. The duration of the anti-apoptotic effect of PTH, thus, depends on the level of Runx2, which in turn is decreased by PTH via Smurf1-mediated proteasomal proteolysis. The self-limiting nature of PTH-induced survival signaling might explain why intermittent administration of the hormone is required for bone anabolism.