Extracellular Molecular Signals Research Articles

Synthetic strategy for the production of electrically polarized polyvinylidene fluoride-trifluoroethylene-co-polymer osseo-functionalized with hydroxyapatite scaffold.

The physiological mechanism of bone tissue regeneration is intricately organized and involves several cell types, intracellular, and extracellular molecular signaling networks. To overcome the drawbacks of autografts and allografts, a number of synthetically produced scaffolds have been manufactured by integrating ceramics, polymers, and their hybrid-composites. Considering the fact that natural bone is composed primarily of collagen and hydroxyapatite, ceramic-polymer composite materials seem to be the most viable alternative to bone implants. Here, in this experimental study, copolymer PVDF-TrFE has been amalgamated with HA ceramics to produce composite scaffolds as bone implants. In order to fabricate PVDF-TrFE-HA (polyvinylidene fluoride-trifluoroethylene-hydroxyapatite) composite scaffolds, solvent casting-particulate leaching technique was devised. Two scaffold specimens were produced, with different PVDF-TrFE and HA molar ratios (70:30 and 50:50), and then electrically polarized to observe the subsequent polarization impact on the tissue growth and the suppression of bacterial cell proliferation. Both the specimens underwent characterization to analyze their biocompatibility and bactericidal activities. The bacterial culture of Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) bacteria on the composites was studied to understand the antibacterial characteristics. Moreover, MG63 cells cultured on these as-formed composites provided information about osteogenesis. Improved osteogenesis and antibacterial efficacy were observed on both the composites. However, the composite with 70 wt% PVDF-TrFE and 30 wt% HA showed a higher bactericidal effect as well as osteogenesis. It was found that PVDF-TrFE-HA-based biomaterials have the potential for bone tissue engineering applications.

Extracellular molecular signals shaping dendrite architecture during brain development.

Proper growth and branching of dendrites are crucial for adequate central nervous system (CNS) functioning. The neuronal dendritic geometry determines the mode and quality of information processing. Any defects in dendrite development will disrupt neuronal circuit formation, affecting brain function. Besides cell-intrinsic programmes, extrinsic factors regulate various aspects of dendritic development. Among these extrinsic factors are extracellular molecular signals which can shape the dendrite architecture during early development. This review will focus on extrinsic factors regulating dendritic growth during early neuronal development, including neurotransmitters, neurotrophins, extracellular matrix proteins, contact-mediated ligands, and secreted and diffusible cues. How these extracellular molecular signals contribute to dendritic growth has been investigated in developing nervous systems using different species, different areas within the CNS, and different neuronal types. The response of the dendritic tree to these extracellular molecular signals can result in growth-promoting or growth-limiting effects, and it depends on the receptor subtype, receptor quantity, receptor efficiency, the animal model used, the developmental time windows, and finally, the targeted signal cascade. This article reviews our current understanding of the role of various extracellular signals in the establishment of the architecture of the dendrites.

Unraveling the effect of intra- and intercellular processes on acetaminophen-induced liver injury

In high dosages, acetaminophen (APAP) can cause severe liver damage, but susceptibility to liver failure varies across individuals and is influenced by factors such as health status. Because APAP-induced liver injury and recovery is regulated by an intricate system of intra- and extracellular molecular signaling, we here aim to quantify the importance of specific modules in determining the outcome after an APAP insult and of potential targets for therapies that mitigate adversity. For this purpose, we integrated hepatocellular acetaminophen metabolism, DNA damage response induction and cell fate into a multiscale mechanistic liver lobule model which involves various cell types, such as hepatocytes, residential Kupffer cells and macrophages. Our model simulations show that zonal differences in metabolism and detoxification efficiency are essential determinants of necrotic damage. Moreover, the extent of senescence, which is regulated by intracellular processes and triggered by extracellular signaling, influences the potential to recover. In silico therapies at early and late time points after APAP insult indicated that prevention of necrotic damage is most beneficial for recovery, whereas interference with regulation of senescence promotes regeneration in a less pronounced way.

Exogenous extracellular matrix proteins decrease cardiac fibroblast activation in stiffening microenvironment through CAPG

Controlling fibrosis is an essential part of regenerating the post-ischemic heart. In the post-ischemic heart, fibroblasts differentiate to myofibroblasts that produce collagen-rich matrix to physically stabilize the infarct area. Infarct models in adult mice result in permanent scarring unlike newborn animals which fully regenerate. Decellularized extracellular matrix (dECM) hydrogels derived from early-aged hearts have been shown to be a transplantable therapy that preserves heart function and stimulates cardiomyocyte proliferation and vascularization. In this study, we investigate the anti-fibrotic effects of injectable dECM hydrogels in a cardiac explant model in the context of age-associated tissue compliance. Treatments with adult and fetal dECM hydrogels were tested for molecular effects on cardiac fibroblast activation and fibrosis. Altered sensitivity of fibroblasts to the mechanosignaling of the remodeling microenvironment was evaluated by manipulating the native extracellular matrix in explants and also with elastomeric substrates in the presence of dECM hydrogels. The injectable fetal dECM hydrogel treatment decreases fibroblast activation and contractility and lowers the stiffness-mediated increases in fibroblast activation observed in stiffened explants. The anti-fibrotic effect of dECM hydrogel is most observable at highest stiffness. Experiments with primary cells on elastomeric substrates with dECM treatment support this phenomenon. Transcriptome analysis indicated that dECM hydrogels affect cytoskeleton related signaling including Macrophage capping protein (CAPG) and Leupaxin (LPXN). CAPG was down-regulated by the fetal dECM hydrogel. LPXN expression was decreased by stiffening the explants; however, this effect was reversed by dECM hydrogel treatment. Pharmacological disruption of cytoskeleton polymerization lowered fibroblast activation and CAPG levels. Knocking down CAPG expression with siRNA inhibited fibroblast activation and collagen deposition. Collectively, fibroblast activation is dependent on cooperative action of extracellular molecular signals and mechanosignaling by cytoskeletal integrity.

The Role of Signaling Pathway on Osteoprogenitor Cell Behavior and Bone Formation

: Different biomarkers and signaling pathways are involved in bone development. These factors lead to different osteoprogenitor cell reactions. Proliferation, migration, and differentiation of osteoprogenitor cells is induced by different intracellular and extracellular molecular signaling pathways. As mesenchymal stem cells (MSCs) and their differentiation during repair and development of bone processes have significant roles, it is believed that sensible molecular signaling pathways involvement is vital to the development of bone formation, bone substitute materials, and bone repair. This study reviews various keys of signaling pathway that terminate proliferation, migration, and differentiation of osteoprogenitor cells.

The roles of signaling pathways in bone repair and regeneration

Regenerative medicine has sparked interest in potential strategies for bone repair. Bone defects are widespread and could be caused by trauma, congenital malformations, infections, and surgery. Although bone has a large self-healing capacity, some defects or fractures are too big to regenerate. To regenerate bone structures which can be used for treatment of patients, bone growth must be induced by a number of bioactive implantable materials, cell types and intracellular, and extracellular molecular signaling pathways. Since mesenchymal stem cells (MSCs) and their differentiation during remodeling processes have important roles in bone regeneration, it is believed that understanding molecular signaling pathways involved is crucial to the development of bone implants, bone substitute materials, and cell-based scaffolds for bone regeneration. In this review, we briefly introduce concepts in fracture repair and regeneration following bone injuries, and then discuss the current clinical methods in bone regeneration. In the next section, we review the involvement of the various key signaling pathways in bone regeneration.

A micro-sequenced CMOS model for cell signalling pathway using G-protein and phosphorylation cascade

Communication between cells in multi-cellular organisms such as animals, humans and plants is essential for co-ordinating the organismic activities of fertilization, growth, survival and reproduction. This bio-chemical communication between trillions of cells in organisms can be more complex than the Internet. This paper develops a CMOS circuit model of signal reception and signal transduction within a cell in response to extra-cellular molecular signals. A micro-sequenced model has been developed where the signal transduction steps are clocked by circadian time intervals. The model converts the chemical signaling pathway into a CMOS multi-step logical transformation cascade transducing a received signal molecule into an activated cellular protein response. This modeling technique leads to understanding cellular malfunctions (diseases) in the form of logical (electrical) faults in a circuit.

Application of Mössbauer spectroscopy for studying chemical effects of environmental factors on microbial signalling: Redox processes involving iron(III) and some microbial autoinducer molecules

Diverse processes of microbial remote intercellular communication as well as the exchange of molecular signals between microbial cells and their host macroorganisms, involving specific low-molecular-mass diffusible substances (used as a ‘chemical language’), are at the peak of current research in biosciences. This fundamental interest is due to the unique possibility of controlling the microbial behaviour and metabolism by influencing merely their signalling pathways. On the other hand, abiotic impact of the environment (medium) on extracellular molecular signals is also of great importance, as any of their chemical interactions (e.g., complexation or oxidation) represent direct interferences in the process of ‘signal delivery’ through the medium. In this work, chemical interactions of microbial extracellular molecular signals (alkylresorcinols (AR), homoserine lactone (HL) – chemical analogues of microbial autoregulatory substances) with iron(III) were monitored using freeze-quench 57Fe Mössbauer spectroscopy in moderately acidic aqueous solutions as well as in the dried solids obtained thereof. The conditions applied were designed to simulate possible processes occurring in soils, where ferric iron is commonly ubiquitous. Gradual reduction of iron(III) by AR was observed, coupled to oxidative degradation of the organics, in solution, while iron(II) also remained dominant upon drying, whereas for HL, some iron(II) was detected in the dried solid only. The iron(III) reduction rate in solution for AR with a longer alkyl chain (4- n-C 6) was found to be much higher than that for the methyl (5-C 1)-substituted derivative, pointing to the importance of the structure (i.e., the position and/or the nature of the alkyl substituent) of the alkylresorcinol molecule for the redox process rate. The results obtained indicate that ARs can be readily oxidised abiotically by soil iron(III) in moderately acidic media, thus being excluded from signalling pathways, which is equal to “message undelivery”, directly affecting microbial autoregulation.

Dendritic morphology and orientation of pyramidal cells of the neocortex in two groups of early postnatal undernourished–rehabilitated rats

Postnatal undernutrition in animals and in humans leads to significant reduction in basal dendritic arborization of layer Vth pyramidal cells of the neocortex. Under the hypothesis that there are critical developmental periods for undernutrition to produce alterations in dendritic differentiation, we studied apical dendritic morphology and orientation of pyramidal cells from the deeper layers of the neocortex in rats undernourished until day 10 (UP10), until weaning (UP21) and in a control group (C). Neurons were stained by the Golgi–Cox method. The main findings are: (i) an increased number of atypically oriented pyramids with apical dendrites extremely short in (UP10) and (UP21) groups and, (ii) the presence of classical pyramids with significantly longer apical dendrites in layers V and VI in (UP10) and (UP21) groups than in the control group (C). We believe that undernutrition may disturb critically the early postnatal brain development by altering intrinsic factors and extracellular molecular signals that guide and regulate the apical dendritic growth of neocortex large pyramidal cells.

Skeleton Crew: Disease gene points to new bone-building signal (Osteoporosis)

From a distance, a suspension bridge appears static. But the ride across reveals constant rebuilding: Workers sandblast and repaint rusted metal, replace decaying rivets, and recast worn roadways. Bones similarly undergo constant maintenance, and when the demolition team works faster than the construction crew, osteoporosis results. To fight this skeletal weakening, scientists have sought to understand how bone renovation is orchestrated. Now, researchers have pinpointed a gene that might play the role of molecular foreman in this process: A defective version of it appears to cause a rare childhood disease with symptoms similar to osteoporosis. The finding identifies a new pathway responsible for bone growth and might lead to the development of drugs that could shore up elderly skeletons. Children with osteoporosis-pseudoglioma syndrome (OPS; also called OPPG), an inherited disorder, suffer from fractures and deformity as a result of abnormally low bone density. They don't appear to make enough bone, although the composition of the bone they do fabricate appears normal. To hunt down the gene responsible for OPS, Gong and colleagues searched a large region of chromosome 11 that they had previously shown contained DNA marker sequences commonly found in patients with the disease. In a small section of this large region, one OPS patient carried three of these genetic markers on both copies of chromosome 11. The researchers wondered whether that stretch harbored a gene that plays a key role in the disease. They zeroed in on a candidate called Lrp5 and sequenced it from members of 28 families afflicted by the disease. Within this group, the researchers found several mutations that probably disrupt the production of normal Lrp5 protein; DNA from normal subjects did not carry the mutations. These results strongly suggest that defective Lrp5 causes OPS, although definitive proof requires further evidence. Previous work on several organisms indicates that Lrp5 and closely related genes encode proteins that coat the surface of cells and bind so-called Wnt proteins, secreted molecules best known for controlling body patterns--limb growth, for example--during embryonic development. To test whether the Wnt signal might also trigger bone growth, the team cultured so-called pluripotent mesenchymal cells, which can become bone cells or other cell types depending on extracellular molecular signals. They engineered the bone cell precursors--which naturally harbor the LRP5 protein--to produce and spew out a Wnt protein--Wnt3a--that the cells don't normally manufacture. Wnt3a production induced activation of genes that are turned on in bone cells if those cells also carry normal LRP5; in contrast, cells that produce a defective form of LRP5 that binds Wnt but can't transmit the signal into the cell didn't show the same bone-related molecular signs. The results suggest that the Wnt pathway, through the action of LRP5, instructs bone-building cells to get cranking and that defects in LRP5 short-circuit that signal and cause OPS. Lrp5 mutations are rare enough that they probably don't contribute to most cases of osteoporosis in the elderly. But by understanding how the pathway directs bone growth, scientists hope to develop drugs that coax the skeletal construction team to work overtime and thereby to prevent osteoporosis in the elderly. An independent investigation also supports the approach: According to work announced in October at the annual meeting of the American Society for Bone and Mineral Research in Phoenix, Arizona, genetic changes in the same region of the chromosome can also lead to unusually high bone density. The area of the genome that contains Lrp5 might well help build a bridge to bone-bolstering treatments. --R. John Davenport Y. Gong et al. (The Osteoporosis-Pseudoglioma Syndrome Collaborative Group), LDL receptor-related protein 5 (LRP5) affects bone accrual and eye development. Cell 107 , 513-523 (2001). [Abstract] [Full Text]