Mechanotransduction via the coordinated actions of integrins,PI3K signaling and Connexin hemichannels

Mechanical loading opens connexin 43(Cx43)hemichannels(HCs),leading to the release of bone anabolic molecules,such as prostaglandins,from mechanosensitive osteocytes,which is essential for bone formation and remodeling.However,the mechanotransduction mechanism that activates HCs remains elusive.Here,we report a unique pathway by which mechanical signals are effectively transferred between integrin molecules located in different regions of the cell,resulting in HC activation.Both integrinα5 andαV were activated upon mechanical stimulation via either fluid dropping or flow shear stress(FSS).Inhibition of integrinαV activation or ablation of integrinα5 prevented HC opening on the cell body when dendrites were mechanically stimulated,suggesting mechanical transmission from the dendritic integrinαV toα5 in the cell body during HC activation.In addition,HC function was compromised in vivo,as determined by utilizing an antibody blockingαV activation andα5-deficient osteocyte-specific knockout mice.Furthermore,inhibition of integrinαV activation,but not that ofα5,attenuated activation of the phosphoinositide 3-kinase(PI3K)-protein kinase B(AKT)signaling pathway upon mechanical loading,and the inhibition of PI3K/AKT activation blocked integrinα5 activation and HC opening.Moreover,HC opening was blocked only by an anti-integrinαV antibody at low but not high FSS levels,suggesting that dendriticαV is a more sensitive mechanosensor thanα5 for activating HCs.Together,these results reveal a new molecular mechanism of mechanotransduction involving the coordinated actions of integrins and PI3K/AKT in osteocytic dendritic processes and cell bodies that leads to HC opening and the release of key bone anabolic factors.

Osteocytes regulate bone anabolic response to mechanical loading in male mice via activation of integrinα5

Physical mechanical stimulation can maintain and even increase bone mass.Here,we report an important role of osteocytic integrinα5 in regulating the anabolic response of bone to mechanical loading using an Itga5 conditional gene knockout(cKO)mouse model.Integrinα5 gene deletion increased apoptotic osteocytes and reduced cortical anabolic responses to tibial compression including decreased endosteal osteoblasts and bone formation,and increased endosteal osteoclasts and bone resorption,contributing to the decreased bone area fraction and biomechanical properties,leading to an enlarged bone marrow area in cKO mice.Similar disruption of anabolic responses to mechanical loading was also detected in cKO trabecular bone.Moreover,integrinα5 deficiency impeded load-induced Cx43 hemichannel opening,and production and release of PGE2,an anabolic factor,resulting in attenuated effects of the loading on catabolic sclerostin(SOST)reduction and anabolicβ-catenin increase.Together,this study shows an indispensable role of integrinα5 in osteocytes in the anabolic action of mechanical loading on skeletal tissue through activation of hemichannels and PGE2-evoked gene expression.Integrinα5 could act as a potential new therapeutic target for bone loss,especially in the elderly population with impeded mechanical sensitivity.

Chaperone proteins as ameliorators of α-synuclein-induced synaptic pathologies: insights into Parkinson’s disease

α-Synuclein accumulation causes synaptic vesicle trafficking defects and may underlie neurodegenerative disorders:Neurodegenerative disorders,such as Parkinson’s disease(PD)and other synucleinopathies,impact the lives of millions of patients and their caregivers.Synucleinopathies include PD,dementia with Lewy Bodies(DLB),multiple system atrophy,and several Alzheimer’s Disease variants.They are clinically characterized by intracellular inclusions called Lewy Bodies,which are rich in atypical aggregates of the protein α-synuclein.While dopaminergic neurons in the substantia nigra are particularly susceptible toα-synuclein-induced aggregation and neurodegeneration,glutamatergic neurons in other brain regions(e.g.cortex)are also frequently affected in PD and other synucleinopathies(Schulz-Schaeffer 2010).

Strategies to enhance shotgun lipidomics for comprehensive analysis of cellular lipids

The discipline of lipidomics, as coined in 2003, has made profound advances and been rapidly expanded. Direct infusion-based shotgun lipidomics contributes a major part of the research in this discipline. However, despite of its numerous advantages over other lipidomics platforms, the classical shotgun lipidomics approach suffers ion suppression and has the difficulties to assess low abundance lipid classes, particularly those less ionizable or that do not yield sensitive and specific fragments. To overcome this obstacle and broaden coverage, strategies have been developed based on unique chemistry and/or physics of lipid classes of interest to enhance shotgun lipidomics. This article overviews the recent enhancements of shotgun lipidomics, including prefractionation, acid/base hydrolysis, derivatization, charge feature utilization. We believe that, by this versatile platform, comprehensive coverage of cellular lipidomes would be achieved in more accurate and effective manner. Therefore, application of the enhanced shotgun lipidomics would greatly accelerate lipidomics research to substantiate the aberrant lipid metabolism, signaling, trafficking, and homeostasis under pathological conditions and their underpinning biochemical mechanisms. It would also facilitate precision medicine studies.

Connexin 43 hemichannels protect bone loss during estrogen deficiency

Estrogen deficiency in postmenopausal women is a major cause of bone loss,resulting in osteopenia,osteoporosis,and a high risk for bone fracture.Connexin 43 (Cx43) hemichannels (HCs) in osteocytes play an important role in osteocyte viability,bone formation,and remodeling.We showed here that estrogen deficiency reduced Cx43 expression and HC function.To determine if functional HCs protect osteocytes and bone loss during estrogen deficiency,we adopted an ovariectomy model in wild-type (WT) and two transgenic Cx43 mice:R76W (dominant-negative mutant inhibiting only gap junction channels) and Cx43 Δ130–136 (dominant-negative mutant compromising both gap junction channels and HCs).The bone mineral density (BMD),bone structure,and histomorphometric changes of cortical and trabecular bones after ovariectomy were investigated.Our results showed that the Δ130–136 transgenic cohort had greatly decreased vertebral trabecular bone mass compared to WT and R76W mice,associated with a significant increase in the number of apoptotic osteocyte and empty lacunae.Moreover,osteoclast surfaces in trabecular and cortical bones were increased after ovariectomy in the R76W and WT mice,respectively,but not in Δ130–136 mice.These data demonstrate that impairment of Cx43 HCs in osteocytes accelerates vertebral trabecular bone loss and increase in osteocyte apoptosis,and further suggest that Cx43 HCs in osteocytes protect trabecular bone against catabolic effects due to estrogen deficiency.

IgG and fibrinogen driven nanoparticle aggregation

A thorough understanding of how proteins induce nanoparticle （NP） aggregation is crucial when designing in vitro and in vivo assays and interpreting experimental results. This knowledge is also crucial when developing nano-applications and formulation for drug delivery systems. In this study, we found that extraction of immunoglobulin G （IgG） from cow serum results in lower polystyrene NPs aggregation. Moreover, addition of isolated IgG or fibrinogen to fetal cow serum enhanced this aggregation, thus demonstrating that these factors are major drivers of NP aggregation in serum. Counter-intuitively, NP aggregation was inversely dependent on protein concentration; i.e., low protein concentrations induced large aggregates, whereas high protein concentrations induced small aggregates. Protein-induced NP aggregation and aggregate size were monitored by absorbance at 400 nm and dynamic light scattering, respectively. Here, we propose a mechanism behind the protein concentration dependent aggregation; this mechanism involves the effects of multiple protein interactions on the NP surface, surface area limitations, aggregation kinetics, and the influence of other serum proteins.

Elemene sensitizes pancreatic cancer cells to bortezomib by enhancing proteasome inhibition via molecular patch mechanism

Dear Editor,Pancreatic cancer*is one of the deadliest cancers,with an overall 5-year survival rate of less than 10%unchanged over the last 40 years.Approximately 80-85%of patients are diagnosed as advanced stage,which are not eligible for curative surgery.1 Therapeutic options for advanced pancreatic cancer patients are still chemotherapy drugs with limited outcomes to improve patient survival and life quality.