scholarly journals Connexin Hemichannels with Prostaglandin Release in Anabolic Function of Bone to Mechanical Loading

2021 ◽  
Author(s):  
Jean Jiang
Keyword(s):  
Bone Formation ◽  
Gap Junction ◽  
Mechanical Loading ◽  
Critical Role ◽  
Dominant Negative ◽  
Osteoblast Activity ◽  
Prostaglandin Release ◽  
Osteogenic Response ◽  
Cortical Bone Mass

Mechanical stimulation, such as physical exercise, is essential for bone formation and health. Here, we demonstrate the critical role of osteocytic Cx43 hemichannels in anabolic function of bone in response to mechanical loading. Two transgenic mouse models, R76W and Δ130-136, expressing dominant-negative Cx43 mutants in osteocytes were adopted. Mechanical loading of tibial bone increased cortical bone mass and mechanical properties in wild-type and gap junction-impaired R76W mice through increased PGE2, endosteal osteoblast activity, and decreased sclerostin. These anabolic responses were impeded in gap junction/hemichannel-impaired Δ130-136 mice and accompanied by increased endosteal osteoclast activity. Specific inhibition of Cx43 hemichannels by Cx43(M1) antibody suppressed PGE2 secretion and impeded loading-induced endosteal osteoblast activity, bone formation and anabolic gene expression. PGE2 administration rescued the osteogenic response to mechanical loading impeded by impaired hemichannels. Together, osteocytic Cx43 hemichannels could be a potential new therapeutic target for treating bone loss and osteoporosis.

The Role of Gap Junction Proteins in Infertility

2010 ◽  
Vol 1 (1) ◽  
pp. 11-18 ◽  
Author(s):  
Piyush Tripathi ◽  
Manorama Tripathi
Keyword(s):  
Gap Junction ◽  
Critical Role ◽  
Growth Control ◽  
Successful Outcome ◽  
Basic Unit ◽  
Junction Protein ◽  
Gap Junction Proteins ◽  
Infertility Patients ◽  
Junction Proteins

ABSTRACT Testis and ovary serve an important role of producing male and female gametes. Their normal functioning is very important for the proper formation of sperm and ovum and thus has a critical role in the successful fertility outcome. Synchronized activity of various cells in the gonads is needed to provide favorable niche for the growth and development of the germ cells. Among various ways of cellular communication, intercellular communication is mediated by gap junctions, which provides open but selective exchange of ion and molecules of restricted size between two adjoining cells. The basic unit of gap junction is connexins. Their important role has been speculated in the maintenance of homeostasis, morphogenesis, cell differentiation, and growth control in higher organisms. The expression of gap junction proteins in reproductive tissues has drawn the attention and interest of researcher to investigate their role in the reproductive outcome. The reports about the correlation of gap junction protein expression pattern in infertility patients and in animal models have suggested their implication in fertility. Some of these gap junction proteins seem to have redundant functions, whereas some could be very critical in the normal fertility and could not be dispensable for the successful outcome of the reproduction.

G-CSF Mediated Decrease in Bone-Marrow SDF-1 Level Is Neutrophil Dependent but CD26 Independent

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 3469-3469
Author(s):  
Pratibha Singh ◽  
Seiji Fukuda ◽  
Janardhan Sampath ◽  
Louis M. Pelus
Keyword(s):  
Bone Marrow ◽  
Magnetic Beads ◽  
Critical Role ◽  
Alternative Mechanism ◽  
Wild Type ◽  
Hematopoietic Stem ◽  
Osteoblast Activity

Abstract Interaction of CXCR4 expressed on hematopoietic stem and progenitor cells (HSPC) with bone-marrow stromal SDF-1 is believed to play a central role in retention or mobilization of HSPC. Recently, a mobilization regimen of G-CSF was shown to decrease osteoblast number resulting in reduced levels of bone-marrow SDF-1, however the detailed mechanism leading to this reduction is currently unknown. It is unlikely that G-CSF directly regulates osteoblast SDF-1 production since osteoblasts do not express G-CSF receptor. Proteolytic cleavage of SDF-1 by peptidase CD26 in the bone-marrow may be an alternative mechanism responsible for reduction of SDF-1 level. Although CD26 can cleave SDF-1 in vitro, direct evidence of SDF-1 cleavage by CD26 in vivo during G-CSF induced HSPC mobilization has not been demonstrated. We previously demonstrated that neutrophils are required for G-CSF induced HSPC mobilization and that CD26 expression on neutrophils, rather than HSPC, is critical for mobilization. To more fully understand the role of CD26 in altering SDF-1 protein/activity during G-CSF induced HSPC mobilization, we quantitated bone-marrow SDF-1 levels in CD26−/− and wild-type CD26+/+ mice by ELISA during G-CSF administration. A standard 4 day G-CSF mobilization regimen (100 μg/kg bid, sc × 4 days) decreased bone-marrow total SDF-1 from 4.55±0.3 to 0.52±0.06 ng/femur in wild-type CD26+/+ mice (8.7-fold) and from 4.51±0.3 to 0.53±0.05 ng/femur (8.5-fold) in CD26−/− mice. However, despite an equivalent decrease in SDF-1, total CFU mobilization and the absolute number of mobilized SKL cells were decreased (3.1 and 2.0 fold lower, respectively) in CD26−/− mice compared to wild-type CD26+/+ controls. These results suggest that the decrease in total SDF-1 level in marrow seen following G-CSF treatment is independent of CD26. Cytological examination of bone-marrow smears showed that the reduction in SDF-1 levels in bone-marrow of both wild-type CD26+/+ and CD26−/− mice following G-CSF administration correlated with an increase in total absolute bone-marrow neutrophil cell number, suggesting a role for neutrophils in modulation of SDF-1 protein. To determine if neutrophils affect osteoblast SDF-1 production, bone marrow Gr-1+ neutrophils from wild-type CD26+/+ and CD26−/− mice were purified using anti-Ly6G magnetic beads and co-cultured with MC3T3-E1 preosteoblasts in vitro. Gr-1+ neutrophils from both wild-type and CD26−/− mice decreased pre-osteoblast SDF-1 production by similar amounts (15.4-fold vs 14.8-fold respectively), while Gr-1 neg cells from both wild-type CD26+/+ or CD26−/− were without effect on SDF-1 levels. Similarly, Gr-1+ neutrophils from both wild-type and CD26−/− mice decreased SDF-1 produced by MC3T3-E1-derived osteoblasts from 1.85±0.3 to 0.52±0.06 ng/ml (3.5 fold) and 0.56±0.07 ng/ml (3.3 fold) respectively, with Gr-1neg cells having no effect. Gr-1+ neutrophils either from wild-type or CD26−/− mice, but not Gr-1neg cells, significantly induced apoptosis of MC3T3-E1 cells as measured by Annexin-V staining (70.5%±10.2 vs 71.2%±12.5 for wild-type CD26+/+ and CD26−/− neutrophils respectively) and significantly inhibited osteoblast activity (20-fold vs 20.6-fold for CD26+/+ and CD26−/− neutrophils respectively) as measured by osteocalcin expression. Furthermore, irrespective of G-CSF treatment, an inverse correlation between absolute neutrophil number and SDF-1 protein levels was observed, suggesting that G-CSF induces neutrophil expansion but does not directly affect SDF-1 production. Collectively, these results provide additional support for the critical role of neutrophils in G-CSF induced mobilization and strongly suggested that neutrophils directly regulate bone-marrow SDF-1 levels independent of CD26 activity.

scholarly journals Osteocyte TSC1 promotes sclerostin secretion to restrain osteogenesis in mice

Open Biology ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 180262 ◽  
Author(s):  
Wen Liu ◽  
Zhenyu Wang ◽  
Jun Yang ◽  
Yongkui Wang ◽  
Kai Li ◽  
...  
Keyword(s):  
Bone Formation ◽  
Mechanical Loading ◽  
Gene Deletion ◽  
Osteoclast Formation ◽  
Rankl Expression ◽  
Mechanistic Target Of Rapamycin ◽  
Mrna And Protein Expression ◽  
Potential Strategy

Osteocytes secrete the glycoprotein sclerostin to inhibit bone formation by osteoblasts, but how sclerostin production is regulated in osteocytes remains unclear. Here, we show that tuberous sclerosis complex 1 (TSC1) in osteocytes promotes sclerostin secretion through inhibition of mechanistic target of rapamycin complex 1 (mTORC1) and downregulation of Sirt1. We generated mice with DMP1 -Cre-directed Tsc1 gene deletion ( Tsc1 CKO) to constitutively activate mTORC1 in osteocytes. Although osteocyte TSC1 disruption increased RANKL expression and osteoclast formation, it markedly reduced sclerostin production in bone, resulting in severe osteosclerosis with enhanced bone formation in mice. Knockdown of TSC1 activated mTORC1 and decreased sclerostin, while rapamycin inhibited mTORC1 and increased sclerostin mRNA and protein expression levels in MLO-Y4 osteocyte-like cells. Furthermore, mechanical loading activated mTORC1 and prevented sclerostin expression in osteocytes. Mechanistically, TSC1 promotes sclerostin production and prevents osteogenesis through inhibition of mTORC1 and downregulation of Sirt1, a repressor of the sclerostin gene Sost . Our findings reveal a role of TSC1/mTORC1 signalling in the regulation of osteocyte sclerostin secretion and bone formation in response to mechanical loading in vitro . Targeting TSC1 represents a potential strategy to increase osteogenesis and prevent bone loss-related diseases.

Neural crest emigration from the neural tube depends on regulated cadherin expression

Development ◽  
1998 ◽  
Vol 125 (15) ◽  
pp. 2963-2971 ◽  
Author(s):  
S. Nakagawa ◽  
M. Takeichi
Keyword(s):  
Neural Crest ◽  
Neural Tube ◽  
Critical Role ◽  
Neural Crest Cells ◽  
Migration Pattern ◽  
Dominant Negative ◽  
Expression Vectors ◽  
Neural Tubes ◽  
Neuroepithelial Cells

During the emergence of neural crest cells from the neural tube, the expression of cadherins dynamically changes. In the chicken embryo, the early neural tube expresses two cadherins, N-cadherin and cadherin-6B (cad6B), in the dorsal-most region where neural crest cells are generated. The expression of these two cadherins is, however, downregulated in the neural crest cells migrating from the neural tube; they instead begin expressing cadherin-7 (cad7). As an attempt to investigate the role of these changes in cadherin expression, we overexpressed various cadherin constructs, including N-cadherin, cad7, and a dominant negative N-cadherin (cN390), in neural crest-generating cells. This was achieved by injecting adenoviral expression vectors encoding these molecules into the lumen of the closing neural tube of chicken embryos at stage 14. In neural tubes injected with the viruses, efficient infection was observed at the neural crest-forming area, resulting in the ectopic cadherin expression also in migrating neural crest cells. Notably, the distribution of neural crest cells with the ectopic cadherins changed depending on which constructs were expressed. Many crest cells failed to escape from the neural tube when N-cadherin or cad7 was overexpressed. Moreover, none of the cells with these ectopic cadherins migrated along the dorsolateral (melanocyte) pathway. When these samples were stained for Mitf, an early melanocyte marker, positive cells were found accumulated within the neural tube, suggesting that the failure of their migration was not due to differentiation defects. In contrast to these phenomena, cells expressing non-functional cadherins exhibited a normal migration pattern. Thus, the overexpression of a neuroepithelial cadherin (N-cadherin) and a crest cadherin (cad7) resulted in the same blocking effect on neural crest segregation from neuroepithelial cells, especially for melanocyte precursors. These findings suggest that the regulation of cadherin expression or its activity at the neural crest-forming area plays a critical role in neural crest emigration from the neural tube.

scholarly journals Liver-derived IGF-I regulates cortical bone mass but is dispensable for the osteogenic response to mechanical loading in female mice

2016 ◽  
Vol 311 (1) ◽  
pp. E138-E144 ◽  
Author(s):  
Johan Svensson ◽  
Sara H. Windahl ◽  
Leanne Saxon ◽  
Klara Sjögren ◽  
Antti Koskela ◽  
...  
Keyword(s):  
Mechanical Strength ◽  
Cortical Bone ◽  
Mechanical Loading ◽  
Cortical Porosity ◽  
Bone Area ◽  
Osteogenic Response ◽  
Igf I ◽  
Cortical Bone Mass ◽  
And Control ◽  
Bone Mechanical Strength

Low circulating IGF-I is associated with increased fracture risk. Conditional depletion of IGF-I produced in osteoblasts or osteocytes inhibits the bone anabolic effect of mechanical loading. Here, we determined the role of endocrine IGF-I for the osteogenic response to mechanical loading in young adult and old female mice with adult, liver-specific IGF-I inactivation (LI-IGF-I−/− mice, serum IGF-I reduced by ≈70%) and control mice. The right tibia was subjected to short periods of axial cyclic compressive loading three times/wk for 2 wk, and measurements were performed using microcomputed tomography and mechanical testing by three-point bending. In the nonloaded left tibia, the LI-IGF-I−/− mice had lower cortical bone area and increased cortical porosity, resulting in reduced bone mechanical strength compared with the controls. Mechanical loading induced a similar response in LI-IGF-I−/− and control mice in terms of cortical bone area and trabecular bone volume fraction. In fact, mechanical loading produced a more marked increase in cortical bone mechanical strength, which was associated with a less marked increase in cortical porosity, in the LI-IGF-I−/− mice compared with the control mice. In conclusion, liver-derived IGF-I regulates cortical bone mass, cortical porosity, and mechanical strength under normal (nonloaded) conditions. However, despite an ∼70% reduction in circulating IGF-I, the osteogenic response to mechanical loading was not attenuated in the LI-IGF-I−/− mice.

scholarly journals Essential Role of STAT3 Signaling in Hair Follicle Homeostasis

2021 ◽  
Vol 12 ◽  
Author(s):  
Kosuke Miyauchi ◽  
Sewon Ki ◽  
Masao Ukai ◽  
Yoshie Suzuki ◽  
Kentaro Inoue ◽  
...  
Keyword(s):  
Hair Follicle ◽  
Inflammatory Responses ◽  
Expression Patterns ◽  
Critical Role ◽  
Dominant Negative ◽  
Cell Specification ◽  
Stat3 Signaling ◽  
Specific Pathogen ◽  
Transcription 3

Dominant-negative mutations associated with signal transducer and activator of transcription 3 (STAT3) signaling, which controls epithelial proliferation in various tissues, lead to atopic dermatitis in hyper IgE syndrome. This dermatitis is thought to be attributed to defects in STAT3 signaling in type 17 helper T cell　specification. However, the role of STAT3 signaling in skin epithelial cells remains unclear. We found that STAT3 signaling in keratinocytes is required to maintain skin homeostasis by negatively controlling the expression of hair follicle-specific keratin genes. These expression patterns correlated with the onset of dermatitis, which was observed in specific pathogen-free conditions but not in germ-free conditions, suggesting the involvement of Toll-like receptor-mediated inflammatory responses. Thus, our study suggests that STAT3-dependent gene expression in keratinocytes plays a critical role in maintaining the homeostasis of skin, which is constantly exposed to microorganisms.

scholarly journals Microphthalmia Gene Product as a Signal Transducer in cAMP-Induced Differentiation of Melanocytes

1998 ◽  
Vol 142 (3) ◽  
pp. 827-835 ◽  
Author(s):  
Corine Bertolotto ◽  
Patricia Abbe ◽  
Timothy J. Hemesath ◽  
Karine Bille ◽  
David E. Fisher ◽  
...  
Keyword(s):  
Pigment Cell ◽  
Critical Role ◽  
Dominant Negative ◽  
Dominant Negative Mutant ◽  
Signal Transducer ◽  
Camp Response Element ◽  
Melanocyte Stimulating Hormone ◽  
Tyrosinase Gene ◽  
Camp Pathway

Melanocyte differentiation characterized by an increased melanogenesis, is stimulated by α-melanocyte–stimulating hormone through activation of the cAMP pathway. During this process, the expression of tyrosinase, the enzyme that controls melanin synthesis is upregulated. We previously showed that cAMP regulates transcription of the tyrosinase gene through a CATGTG motif that binds microphthalmia a transcription factor involved in melanocyte survival. Further, microphthalmia stimulates the transcriptional activity of the tyrosinase promoter and cAMP increases the binding of microphthalmia to the CATGTG motif. These observations led us to hypothesize that microphthalmia mediates the effect of cAMP on the expression of tyrosinase. The present study was designed to elucidate the mechanism by which cAMP regulates microphthalmia function and to prove our former hypothesis, suggesting that microphthalmia is a key component in cAMP-induced melanogenesis. First, we showed that cAMP upregulates the transcription of microphthalmia gene through a classical cAMP response element that is functional only in melanocytes. Then, using a dominant-negative mutant of microphthalmia, we demonstrated that microphthalmia is required for the cAMP effect on tyrosinase promoter. These findings disclose the mechanism by which cAMP stimulates tyrosinase expression and melanogenesis and emphasize the critical role of microphthalmia as signal transducer in cAMP-induced melanogenesis and pigment cell differentiation.

scholarly journals Requirement of the juxtamembrane domain of the cadherin cytoplasmic tail for morphogenetic cell rearrangement during myotome development

2001 ◽  
Vol 155 (7) ◽  
pp. 1297-1306 ◽  
Author(s):  
Kazuki Horikawa ◽  
Masatoshi Takeichi
Keyword(s):  
Cell Adhesion Molecules ◽  
Critical Role ◽  
Cytoplasmic Tail ◽  
Embryonic Cell ◽  
Dominant Negative ◽  
Regulatory Function ◽  
Juxtamembrane Domain ◽  
Cell Rearrangement ◽  
Adhesion System

During development, the activity of cadherin cell adhesion molecules is assumed to be regulated to allow for cell rearrangement or translocation. Previous studies suggest that the juxtamembrane (JM) domain of the cadherin cytoplasmic tail, which contains the site for binding to p120ctn, has a regulatory function in this adhesion system. To study the possible role of JM domain–dependent cadherin regulation in embryonic cell rearrangement, we ectopically expressed a series of N-cadherin mutants in developing somites of chicken embryos. When a JM domain–deficient N-cadherin was expressed, the morphogenetic expansion of the myotome was strongly suppressed. However, a triple alanine substitution in the JM domain, which specifically inhibited the p120ctn binding, had no effect on myotome development. Furthermore, a dominant negative N-cadherin, which had a deletion at the extracellular domain but maintained the normal cytoplasmic tail, did not affect myotome expansion; although it disrupted intersomite boundaries. Overexpression of p120ctn also did not affect myotome expansion, but it did perturb myofiber orientation. These and other observations suggest that the JM domain of N-cadherin has a regulatory role in myotome cell rearrangement in which molecules other than p120ctn are involved. The p120ctn molecule itself seems to play a critical role in the arrangement of myofibers.

scholarly journals The Type 1 Insulin-Like Growth Factor Receptor (IGF-IR) Pathway Is Mandatory for the Follistatin-Induced Skeletal Muscle Hypertrophy

Endocrinology ◽  
2012 ◽  
Vol 153 (1) ◽  
pp. 241-253 ◽  
Author(s):  
S. Kalista ◽  
O. Schakman ◽  
H. Gilson ◽  
P. Lause ◽  
B. Demeulder ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Knockout Mice ◽  
Muscle Hypertrophy ◽  
Critical Role ◽  
Muscle Growth ◽  
Dominant Negative ◽  
Wild Type ◽  
Myostatin Inhibition

Myostatin inhibition by follistatin (FS) offers a new approach for muscle mass enhancement. The aim of the present study was to characterize the mediators responsible for the FS hypertrophic action on skeletal muscle in male mice. Because IGF-I and IGF-II, two crucial skeletal muscle growth factors, are induced by myostatin inhibition, we assessed their role in FS action. First, we tested whether type 1 IGF receptor (IGF-IR) is required for FS-induced hypertrophy. By using mice expressing a dominant-negative IGF-IR in skeletal muscle, we showed that IGF-IR inhibition blunted by 63% fiber hypertrophy caused by FS. Second, we showed that FS caused the same degree of fiber hypertrophy in wild-type and IGF-II knockout mice. We then tested the role of the signaling molecules stimulated by IGF-IR, in particular the Akt/mammalian target of rapamycin (mTOR)/70-kDa ribosomal protein S6 kinase (S6K) pathway. We investigated whether Akt phosphorylation is required for the FS action. By cotransfecting a dominant-negative form of Akt together with FS, we showed that Akt inhibition reduced by 65% fiber hypertrophy caused by FS. Second, we evaluated the role of mTOR in FS action. Fiber hypertrophy induced by FS was reduced by 36% in rapamycin-treated mice. Finally, because the activity of S6K is increased by FS, we tested its role in FS action. FS caused the same degree of fiber hypertrophy in wild-type and S6K1/2 knockout mice. In conclusion, the IGF-IR/Akt/mTOR pathway plays a critical role in FS-induced muscle hypertrophy. In contrast, induction of IGF-II expression and S6K activity by FS are not required for the hypertrophic action of FS.

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