RESUMO
Complications of Crohn's disease reach far beyond postsurgical leak, infection, and enterocutaneous fistula. Malnutrition, intestinal failure, and recurrent disease all will require ongoing attentions. The management of these patients may further be complicated by the need for chronic immunosuppression. The underlying principles continue to include optimization of nutritional status, and preservation of bowel length when possible. However, there have been several recent advances in both the medical and surgical management of the disease. Understanding the contribution of the mesentery to inflammation, new surgical techniques such as the Kono-S anastomosis and extended mesenteric resection is decreasing the need for repeated resections.
Assuntos
Doença de Crohn , Humanos , Doença de Crohn/complicações , Doença de Crohn/cirurgia , Complicações Pós-Operatórias/epidemiologia , Fístula Intestinal/etiologia , Fístula Intestinal/cirurgiaRESUMO
Age-related bone loss is an important risk factor for fractures in the elderly; it results from an imbalance in bone remodeling mainly due to decreased bone formation. We have previously demonstrated that endogenous G protein-coupled receptor (GPCR)-driven Gi signaling in osteoblasts (Obs) restrains bone formation in mice during growth. Here, we launched a longitudinal study to test the hypothesis that Gi signaling in Obs restrains bone formation in aging mice, thereby promoting bone loss. Our approach was to block Gi signaling in maturing Obs by the induced expression of the catalytic subunit of pertussis toxin (PTX) after the achievement of peak bone mass. In contrast to the progressive cancellous bone loss seen in aging sex-matched littermate control mice, aging female Col1(2.3)+/PTX+ mice showed an age-related increase in bone volume. Increased bone volume was associated with increased bone formation at both trabecular and endocortical surfaces as well as increased bending strength of the femoral middiaphyses. In contrast, male Col1(2.3)+/PTX+ mice were not protected from age-related bone loss. Our results indicate that Gi signaling markedly restrains bone formation at cancellous and endosteal bone surfaces in female mice during aging. Blockade of the relevant Gi-coupled GPCRs represents an approach for the development of osteoporosis therapies-at least in the long bones of aging women.
Assuntos
Subunidades alfa Gi-Go de Proteínas de Ligação ao GTP/fisiologia , Osteoblastos/metabolismo , Osteoporose/genética , Animais , Densidade Óssea/efeitos dos fármacos , Densidade Óssea/genética , Remodelação Óssea/efeitos dos fármacos , Remodelação Óssea/genética , Colágeno Tipo I/genética , Cadeia alfa 1 do Colágeno Tipo I , Feminino , Subunidades alfa Gi-Go de Proteínas de Ligação ao GTP/metabolismo , Masculino , Camundongos , Camundongos Transgênicos , Osteogênese/efeitos dos fármacos , Osteogênese/genética , Osteoporose/metabolismo , Osteoporose/patologia , Toxina Pertussis/genética , Transdução de Sinais/fisiologiaRESUMO
Epidemiological studies show that high circulating levels of adiponectin are associated with low bone mineral density. The effect of adiponectin on skeletal homeostasis, on osteoblasts in particular, remains controversial. We investigated this issue using mice with adipocyte-specific over-expression of adiponectin (AdTg). MicroCT and histomorphometric analysis revealed decreases (15%) in fractional bone volume in AdTg mice at the proximal tibia with no changes at the distal femur. Cortical bone thickness at mid-shafts of the tibia and at the tibiofibular junction was reduced (3-4%) in AdTg mice. Dynamic histomorphometry at the proximal tibia in AdTg mice revealed inhibition of bone formation. AdTg mice had increased numbers of adipocytes in close proximity to trabecular bone in the tibia, associated with increased adiponectin levels in tibial marrow. Treatment of BMSCs with adiponectin after initiation of osteoblastic differentiation resulted in reduced mineralized colony formation and reduced expression of mRNA of osteoblastic genes, osterix (70%), Runx2 (52%), alkaline phosphatase (72%), Col1 (74%), and osteocalcin (81%). Adiponectin treatment of differentiating osteoblasts increased expression of the osteoblast genes PPARγ (32%) and C/ebpα (55%) and increased adipocyte colony formation. These data suggest a model in which locally produced adiponectin plays a negative role in regulating skeletal homeostasis through inhibition of bone formation and by promoting an adipogenic phenotype.
Assuntos
Adiponectina/fisiologia , Osso e Ossos/fisiologia , Adiponectina/biossíntese , Tecido Adiposo/citologia , Animais , Camundongos , Camundongos Transgênicos , Osteoblastos/citologiaRESUMO
G-protein-coupled receptors (GPCRs) are key regulators of skeletal homeostasis and are likely important in fracture healing. Because GPCRs can activate multiple signaling pathways simultaneously, we used targeted disruption of G(i) -GPCR or activation of G(s) -GPCR pathways to test how each pathway functions in the skeleton. We previously demonstrated that blockade of G(i) signaling by pertussis toxin (PTX) transgene expression in maturing osteoblastic cells enhanced cortical and trabecular bone formation and prevented age-related bone loss in female mice. In addition, activation of G(s) signaling by expressing the G(s) -coupled engineered receptor Rs1 in maturing osteoblastic cells induced massive trabecular bone formation but cortical bone loss. Here, we test our hypothesis that the G(i) and G(s) pathways also have distinct functions in fracture repair. We applied closed, nonstabilized tibial fractures to mice in which endogenous G(i) signaling was inhibited by PTX, or to mice with activated G(s) signaling mediated by Rs1. Blockade of endogenous G(i) resulted in a smaller callus but increased bone formation in both young and old mice. PTX treatment decreased expression of Dkk1 and increased Lef1 mRNAs during fracture healing, suggesting a role for endogenous G(i) signaling in maintaining Dkk1 expression and suppressing Wnt signaling. In contrast, adult mice with activated Gs signaling showed a slight increase in the initial callus size with increased callus bone formation. These results show that G(i) blockade and G(s) activation of the same osteoblastic lineage cell can induce different biological responses during fracture healing. Our findings also show that manipulating the GPCR/cAMP signaling pathway by selective timing of G(s) and G(i) -GPCR activation may be important for optimizing fracture repair.
Assuntos
AMP Cíclico/metabolismo , Consolidação da Fratura/genética , Fraturas Ósseas , Osteoblastos/metabolismo , Receptores Acoplados a Proteínas G/genética , Sistemas do Segundo Mensageiro , Animais , AMP Cíclico/genética , Feminino , Fraturas Ósseas/genética , Fraturas Ósseas/metabolismo , Fraturas Ósseas/patologia , Subunidades alfa Gi-Go de Proteínas de Ligação ao GTP/genética , Subunidades alfa Gi-Go de Proteínas de Ligação ao GTP/metabolismo , Peptídeos e Proteínas de Sinalização Intercelular/genética , Peptídeos e Proteínas de Sinalização Intercelular/metabolismo , Fator 1 de Ligação ao Facilitador Linfoide/genética , Fator 1 de Ligação ao Facilitador Linfoide/metabolismo , Camundongos , Camundongos Transgênicos , Osteoblastos/patologiaRESUMO
Available evidence indicates that some Tie2-expressing (Tie2(+) ) cells serve as multipotent progenitors that have robust BMP-dependent osteogenic activity and mediate heterotopic ossification (HO). Since signaling through the G protein Gi is required for cell motility, we hypothesized that blockade of endogenous Gi signaling in Tie2(+) cell populations would prevent HO formation. Blockade of Gi signaling in Tie2(+) cells was accomplished in transgenic mice with expression of pertussis toxin (PTX) under the control of the Tie2 promoter (Tie2(+) /PTX(+) ). Bone formation within HOs was evaluated 2 weeks after BMP injection. Expression of PTX in Tie2(+) cells significantly reduced the bone volume (BV) of HOs in male and female mice. Orthotopic bones were assessed at the distal femur and expression of PTX significantly increased trabecular bone fractional volume and bone formation rate in females only. In adult Tie2(+) /GFP(+) mice, GFP(+) cells appeared both inside and at the surfaces of bone tissue within HOs and in orthotopic bones. In summary, blockade of Gi signaling in Tie2(+) cells reduced the accrual of HOs and stimulated osteogenesis in orthotopic bones. Targeting of Gi protein coupled receptors in Tie2(+) cells may be a novel therapeutic strategy in states of abnormal bone formation such as osteoporosis and HO.
Assuntos
Subunidades alfa Gi-Go de Proteínas de Ligação ao GTP/fisiologia , Ossificação Heterotópica/fisiopatologia , Osteogênese , Receptor TIE-2/análise , Transdução de Sinais/fisiologia , Animais , Feminino , Masculino , Camundongos , Camundongos Transgênicos , Caracteres SexuaisRESUMO
G protein-coupled receptor (GPCR) signaling in osteoblasts (OBs) is an important regulator of bone formation. We previously described a mouse model expressing Rs1, an engineered constitutively active Gs-coupled GPCR, under the control of the 2.3 kb Col I promoter. These mice showed a dramatic age-dependent increase in trabecular bone of femurs. Here, we further evaluated the effects of enhanced Gs signaling in OBs on intramembranous bone formation by examining calvariae of 1- and 9-week-old Col1(2.3)/Rs1 mice and characterized the in vivo gene expression specifically occurring in osteoblasts with activated Gs G protein-coupled receptor signaling, at the cellular level rather than in a whole bone. Rs1 calvariae displayed a dramatic increase in bone volume with partial loss of cortical structure. By immunohistochemistry, Osterix was detected in cells throughout the inter-trabecular space while Osteocalcin was expressed predominantly in cells along bone surfaces, suggesting the role of paracrine mediators secreted from OBs driven by 2.3 kb Col I promoter could influence early OB commitment, differentiation, and/or proliferation. Gene expression analysis of calvarial OBs revealed that genes affected by Rs1 signaling include those encoding proteins important for cell differentiation, cytokines and growth factors, angiogenesis, coagulation, and energy metabolism. The set of Gs-GPCRs and other GPCRs that may contribute to the observed skeletal phenotype and candidate paracrine mediators of the effect of Gs signaling in OBs were also determined. Our results identify novel detailed in vivo cellular changes of the anabolic response of the skeleton to Gs signaling in mature OBs.
Assuntos
Subunidades alfa Gs de Proteínas de Ligação ao GTP/fisiologia , Osteoblastos/metabolismo , Transcriptoma , Animais , Regeneração Óssea , Células Cultivadas , Fator 9 de Crescimento de Fibroblastos/genética , Fator 9 de Crescimento de Fibroblastos/metabolismo , Camundongos Transgênicos , Análise de Sequência com Séries de Oligonucleotídeos , Osteogênese , Receptores Acoplados a Proteínas G/genética , Receptores Acoplados a Proteínas G/metabolismo , Transdução de Sinais , Crânio/patologia , Crânio/fisiopatologia , Fator de Transcrição Sp7 , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
Adipose tissue plays an important role in skeletal homeostasis, and there is interest in identifying adipokines that influence bone mass. One such adipokine may be apelin, a ligand for the Gi-G protein-coupled receptor APJ, which has been reported to enhance mitogenesis and suppress apoptosis in MC3T3-E1 cells and primary human osteoblasts (OBs). However, it is unclear whether apelin plays a physiological role in regulating skeletal homeostasis in vivo. In this study, we compared the skeletal phenotypes of apelin knockout (APKO) and wild-type mice and investigated the direct effects of apelin on bone cells in vitro. The increased fractional cancellous bone volume at the distal femur was observed in APKO mice of both genders at 12 weeks of age and persisted until the age of 20. Cortical bone perimeter at the femoral midshaft was significantly increased in males and females at both time points. Dynamic histomorphometry revealed that APKO mice had increased rates of bone formation and mineral apposition, with evidences of accelerated OB proliferation and differentiation, without significant alteration in osteoclast activity. An in vitro study showed that apelin increased proliferation of primary mouse OBs as well as suppressed apoptosis in a dose-dependent manner with the maximum effect at 5nM. However, it had no effect on the formation of mineralized nodules. We did not observed significantly altered in osteoclast parameters in vitro. Taken together, the increased bone mass in mice lacking apelin suggested complex direct and paracrine/endocrine effects of apelin on bone, possibly via modulating insulin sensitivity. These results indicate that apelin functions as a physiologically significant antianabolic factor in bone in vivo.
Assuntos
Adipocinas/genética , Densidade Óssea , Peptídeos e Proteínas de Sinalização Intercelular/genética , Osteogênese , Adipocinas/metabolismo , Animais , Apelina , Apoptose , Proliferação de Células , Células Cultivadas , Subunidade alfa 1 de Fator de Ligação ao Core/genética , Subunidade alfa 1 de Fator de Ligação ao Core/metabolismo , Feminino , Fêmur/metabolismo , Expressão Gênica , Peptídeos e Proteínas de Sinalização Intercelular/metabolismo , Masculino , Camundongos , Camundongos da Linhagem 129 , Camundongos Endogâmicos C57BL , Camundongos Knockout , Osteoblastos/citologia , Osteoblastos/metabolismo , Osteoclastos/citologia , Osteoclastos/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Tíbia/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Microtomografia por Raio-XRESUMO
Osteocytes have been implicated in the control of bone formation. However, the signal transduction pathways that regulate the biological function of osteocytes are poorly defined. Limited evidence suggests an important role for the Gs/cAMP pathway in osteocyte function. In the present study, we explored the hypothesis that cAMP-dependent kinase A (PKA) activation in osteocytes plays a key role in controlling skeletal homeostasis. To test this hypothesis, we mated mice harboring a Cre-conditional, mutated PKA catalytic subunit allele that encodes a constitutively active form of PKA (CαR) with mice expressing Cre under the control of the osteocyte-specific promoter, DMP1. This allowed us to direct the expression of CαR to osteocytes in double transgenic progeny. Examination of Cre expression indicated that CαR was also expressed in late osteoblasts. Cortical and trabecular bone parameters from 12-week old mice were determined by µCT. Expression of CαR in osteocytes and late osteoblasts altered the shape of cortical bone proximal to the tibia-fibular junction (TFJ) and produced a significant increase in its size. In trabecular bone of the distal femur, fractional bone volume, trabecular number, and trabecular thickness were increased. These increases were partially the results of increased bone formation rates (BFRs) on the endosteal surface of the cortical bone proximal to the TFJ as well as increased BFR on the trabecular bone surface of the distal femur. Mice expressing CαR displayed a marked increase in the expression of osteoblast markers such as osterix, runx2, collagen 1α1, and alkaline phosphatase (ALP). Interestingly, expression of osteocyte marker gene, DMP1, was significantly up-regulated but the osteocyte number per bone area was not altered. Expression of SOST, a presumed target for PKA signaling in osteocytes, was significantly down-regulated in females. Importantly, no changes in bone resorption were detected. In summary, constitutive PKA signaling in osteocytes and late osteoblasts led to a small expansion of the size of the cortical bone proximal to the TFJ and an increase in trabecular bone in female mice. This was associated with down-regulation of SOST and up-regulation of several osteoblast marker genes. Activation of the PKA pathway in osteocytes and late osteoblasts is sufficient for the initiation of an anabolic skeletal response.