Synthesis Of New Tissue Research Articles

Mesenchymal stem cells in animal reproduction: sources, uses and scenario.

Studies regarding mesenchymal stem cells turned up in the 1960's and this cell type created a great number of questions about its functions and applicability in science and medicine. When used with therapeutic intent, these cells present an inclination to migrate to sites of injury, inflammation or disease, where they secrete bioactive factors that stimulates the synthesis of new tissue. In this context, studies using rodents reported that MSCs promoted positive effects in the ovarian function in mice with premature aging of follicular reserve. In female bovines, experimental stem cell-based therapies have been used to either generate new oocytes with in vitro quality or stimulate such action in vivo. It is also reported, that the intraovarian application of mesenchymal stem cells generates a greater production of embryos in vitro and the production of early and expanded blastocysts. Additionally, analysis of ovarian tissue in animal subjected to treatment showed an increase in the number of developing follicles. Nevertheless, the treatments involving stem cells with different modes of application, different sources and different species were able to act on the hormonal, tissue, cellular and metabolic levels, generating positive results in the recovery and improvement of ovarian functions.

Overview of the biological activity of polyacrylamide hydrogels

Recent research on the biological activity of polyacrylamide represents a significant advance in science. Long-standing applications for the chemical compound polyacrylamide include wastewater treatment and food production. Recent research has revealed that this substance has a biological activity that may be exploited to control the functioning of other biological systems.
 According to certain studies, polyacrylamide may interact with proteins and other molecules to change their function. For instance, it may have an impact on proteases' ability to degrade proteins. Receptors, which are molecules that react to outside signals, can also be affected by their activity. Additionally, the study group discovered that polyacrylamide can function as a scaffold for cells, offering a framework for the synthesis of new tissue and organs.

Degradation mechanism and increased stability of chitosan-based hybrid scaffolds cross-linked with nanostructured carbon: Process–structure–functional property relationship

The degradation behavior of porous scaffolds plays an important role in the synthesis of new tissue. In this study, three-dimensional hybrid porous scaffolds of chitosan (CS) comprised of nanostructured carbon (graphene oxide (GO) and single-walled carbon nanohorns (SWCNH)) were prepared by freeze-drying method. In-vitro degradation behavior of scaffolds was investigated up to 8 weeks in phosphate buffer saline (PBS) solution at 37 °C. The characteristics of scaffolds explored as a function of degradation time include crystalline structure, pore morphology, molecular weight, and wet/dry weight. The pH value of the PBS solution during degradation was also monitored. The study demonstrates for the first time that hybrid chitosan scaffolds with nanostructured carbon (GO and SWCNH) are potentially more stable than pure chitosan scaffolds during the time period required for tissue regeneration. The stability of hybrid scaffolds is attributed to nanostructured carbon that was processed with the objective that it is present in a robust manner via a highly cross-linked dense network structure. The chemical structure of chitosan was disrupted within a short period of two weeks, while disruption occurred in hybrid scaffolds after eight weeks. This was accompanied by a weight loss of ∼28% in pure chitosan and ∼20% in hybrid scaffolds. Furthermore, the degraded products were of low molecular weight in pure chitosan and high molecular weight in hybrid chitosan scaffolds. This led to significant decrease in the pH of solution to ∼6.2 in pure chitosan and to ∼7.2 in hybrid scaffolds. The observations clearly underscore that the introduction of GO and SWCNH via cross-link mechanism in CS is a potentially viable approach to tune the degradation rate of hybrid scaffolds in tissue engineering.

Regulation of fibroblast migration by tenascin-C

Synthesis of new tissue by fibroblasts is required for tissue rebuilding in response to injury. Fibroblast migration from surrounding healthy tissue into the fibrin-fibronectin provisional matrix deposited upon injury is a key rate-limiting step of this stage of tissue repair. These events must be tightly regulated. Excessive deposition of scar tissue is the major hallmark of fibrotic disease. Tenascin-C is an extracellular matrix glycoprotein that is transiently expressed upon tissue injury, where it is specifically localized to the wound edge, and persistently up-regulated in fibrotic disease. We have shown that full-length tenascin-C promotes fibroblast migration within fibrin-fibronectin matrices and we have mapped the domains within the molecule critical for enhancing migration. We also demonstrated that specific fragments of tenascin-C inhibit fibroblast migration. These results suggest that transient expression of tenascin-C at the wound boundary is key to tissue repair: its induction recruits fibroblasts into the wound and fragments resulting from its breakdown prevent excessive fibroblast infiltration. Our results demonstrate how fibroblast migration in three-dimensional provisional matrices may be differentially regulated by proteolysis of matrix molecules and could explain how persistent expression of tenascin-C contributes to the progression of fibrotic disease.

Mechanosensing and Mechanochemical Transduction: How Is Mechanical Energy Sensed and Converted Into Chemical Energy in an Extracellular Matrix?

Gravity plays a central role in vertebrate development and evolution. Gravitational forces acting on mammalian tissues cause the net muscle forces required for locomotion to be higher on earth than on a body subjected to a microgravitational field. As body mass increases during development, the musculoskeleton must be able to adapt by increasing the size of its functional units. Thus mechanical forces required to do the work (mechanical energy) of locomotion must be sensed by cells and converted into chemical energy (synthesis of new tissue). Extracellular matrices (ECMs) are multicomponent tissues that transduce internal and external mechanical signals into changes in tissue structure and function through a process termed mechanochemical transduction. Under the influence of an external gravitational field, both mineralized and unmineralized vertebrate tissues exhibit internal tensile forces that serve to preserve a synthetic phenotype in the resident cell population. Application of additional external forces alters the balance between the external gravitational force and internal forces acting on resident cells leading to changes in the expression of genes and production of protein that ultimately may alter the exact structure and function of the extracellular matrix. Changes in the equilibrium between internal and external forces acting on ECMs and changes in mechanochemical transduction processes at the cellular level appear to be important mechanisms by which mammals adjust their needs to store, transmit, and dissipate energy that is required during development and for bodily movements. Mechanosensing is postulated to involve many different cellular and extracellular components. Mechanical forces cause direct stretching of protein-cell surface integrin binding sites that occur on all eukaryotic cells. Stress-induced conformational changes in the extracellular matrix may alter integrin structure and lead to activation of several secondary messenger pathways within the cell. Activation of these pathways leads to altered regulation of genes that synthesize and catabolize extracellular matrix proteins as well as to alterations in cell division. Another aspect by which mechanal signals are transduced involves deformation of gap junctions containing calcium-sensitive stretch receptors. Once activated, these channels trigger secondary messenger activation through pathways similar to those involved in integrin-dependent activation and allow cell-to-cell communications between cells with similar and different phenotypes. Another process by which mechanochemical transduction occurs is through the activation of ion channels in the cell membrane. Mechanical forces have been shown to alter cell membrane ion channel permeability associated with Ca(+2) and other ion fluxes. In addition, the application of mechanical forces to cells leads to the activation of growth factor and hormone receptors even in the absence of ligand binding. These are some of the mechanisms that have evolved in vertebrates by which cells respond to changes in external forces that lead to changes in tissue strcture and function.

Seasonality of in situ respiration rate in three temperate benthic suspension feeders

Natural respiration rates of suspension feeders in temperate ecosystems are still poorly known. This lack of information constrains our understanding of the functioning and dynamics of benthic marine ecosystems in temperate areas.We examined the in situ seasonal variation in respiration rate of three benthic suspension feeders (a sponge, an ascidian, and a gorgonian) in northwestern Mediterranean sublittoral communities using a recirculating flow respirometry system. The in situ technique is shown to be highly applicable to seasonal studies of the physiological energetics of benthic suspension feeders. Respiration rates of the three species varied two‐ to threefold through the annual cycle, exhibiting a marked seasonal pattern but showing no daily cycle or significant day‐today variability within months. The respiration rate of the sponge and ascidian, active suspension feeders, increased with temperature. The respiration rate of the gorgonian, a passive suspension feeder, did not correlate with temperature. We estimated a Q10 of 1.1, which indicates that respiration rate in this species is not highly dependent on temperature. Synthesis of new tissue of some Mediterranean benthic suspension feeders, such as gorgonians, does not correlate with temperature, which allowed us to isolate the effects of temperature and synthesis of new tissue on respiration rate. Synthesis of new tissue increased respiration rate of the gorgonian by ~40%. The low rate of synthesis of new tissue during summer, together with the contraction of polyps and the low Q10, explains the low respiration rates of the gorgonian observed during the period of highest temperature. These low respiration rates support the hypothesis that energy limitations may underlie summer dormancy in some benthic suspension‐feeding taxa in the Mediterranean.

Contrasts in the capacity and underlying mechanisms for compensatory growth in two pelagic marine fishes

The widespread capacity for teleost fishes to engage in compensatory growth suggests there are costs or trade-offs that constrain normal growth to sub-maximal rates. Some potential trade- offs include behavioral conflicts between foraging and avoiding predators, and physiological aspects of energy allocation between synthesis of new tissue and functional demands of metabolism and maintenance. We examined the capacity for compensation and some potential underlying mecha- nisms in juveniles of 2 northern Pacific fish species, walleye pollock Theragra chalcogramma and sablefish Anoplopoma fimbria. Fish were deprived of food for 2 to 3 wk, then returned to ad libitum rations. Growth rates were subsequently compared to those for continually fed fish for up to 16 wk, and potential trade-offs in behavior (food consumption, routine swimming speeds, and response to a predator) and physiology (indexed by critical swimming speeds) were examined during 3 time peri- ods: immediately after deprivation, after 4 wk of ad libitum rations, and after 9 wk. We distinguished between routine swimming speeds, which indicate volitional motor activity, and critical swimming speeds, which estimate physiological capacity by forcing fish to swim to exhaustion against an increasing current. Previously deprived walleye pollock exhibited a clear, sustained capacity for accelerated growth, allowing them to quickly catch up in size to continually fed fish. Sablefish, how- ever, exhibited only a minor level of growth compensation. Underlying mechanisms of compensatory growth also differed between the 2 species. Previously deprived walleye pollock increased food con- sumption to levels 3 to 4× greater than those of control fish and reduced energy expenditure by low- ering routine swimming speeds. Compensating sablefish did not differ from control fish in consump- tion rates or routine swimming, but had lower critical swimming speeds than control fish, suggesting a trade-off in energy allocation. Responses to a simulated predator threat did not differ between pre- viously deprived and continually fed fish of either species. The experimental results are suggestive of different mechanisms, behaviorally based for walleye pollock and physiologically based for sablefish, associated with accelerated growth. The differences between the 2 species in integrated processes of growth, behavior, and physiology are likely to be a function of their contrasting life history strategies and different baseline growth rates.

The transcription factor Egr-1: a potential drug in wound healing and tissue repair

In the United States, between 40 and 90 million hospital days are lost per year as a result of trauma and surgical procedures which result in the loss of functional tissue. This is estimated to cost the economy and healthcare providers in excess of US $500 billion, a figure that is increasing because of extending population lifespan. Tissue engineering and gene therapies are radical new treatments that are aimed at tissue regeneration ranging from dermal, osteal and occular repair to the replacement of failing tissue with entire biosynthetic organs. Over the last decade, numerous proteins have been identified that are able to direct the synthesis of new tissue. Such proteins include growth factors, cytokines and, more recently, transcription factors.

Potential Renal Solute Load: Considerations Relating to Complementary Feedings of Breastfed Infants

Renal solute load (RSL) refers to all solutes of endogenous or dietary origin that require excretion by the kidneys. Potential renal solute load (PRSL) refers to solutes of dietary origin that would need to be excreted in the urine if none were diverted into synthesis of new tissue and none were lost through nonrenal routes.PRSL=N/28+Na+Cl+K+Pawhere N is nitrogen, Na is sodium, Cl is chloride, K is potassium and Pa is available phosphorus, and the units are in millimoles (or milliosmoles), except for N, which is total N in mg. The term N/28 represents nitrogenous solutes (mmol) based on the assumption that the modal number of N atoms per molecule is 2. Pa is equal to total P except in soy-based diets, in which Pa is about two-thirds of total P.When an infant is well and consuming a predominantly liquid diet, the renal concentrating ability of nearly all infants is sufficient to maintain water balance even if the feeding provides a PRSL as high as that of cows' milk. When an infant is ill, does not grow, and does not have diarrhea, PRSL is nearly the same as RSL. PRSL is an important consideration in maintaining water balance in the following 3 circumstances: 1) during acute illness, when fluid intake is decreased, especially if the illness is accompanied by fever; 2) when an energy-dense diet is fed; and 3) when renal concentrating ability is decreased, as in chronic renal disease and diabetes insipidus.Calculations of the PRSL of various infant foods are presented in Table 1. Beikost in the United States provides 2.4 g protein per 100 kcal, which may be greater than in many lesser industrialized countries.A number of studies3–7 have demonstrated that nearly all breastfed infants who are otherwise well maintain satisfactory water balance in hot environments.To illustrate the effect of feeding beikost on water balance during illness, Table 2 presents calculations regarding a hypothetic 6-month-old, 7-kg infant fed varying quantities of human milk and beikost. It is evident from the calculations that replacement of some of the human milk intake with beikost will have a slightly negative effect on water balance whereas increasing the total fluid intake, either by achieving greater consumption of human milk or a combination of human milk and beikost, despite a concurrent increase in PRSL, will have a major beneficial effect on water balance. Thus, during illness if the feeding of beikost is accompanied by increase in total volume of intake, water balance will be improved.

REVIEW Towards an explanation of crop nitrogen demand based on the optimization of leaf nitrogen per unit leaf area

An area of plant science that is still uncertain is precisely what determines plants' demand for nitrogen (N), that is the amount of N they need to take up from the soil to meet their requirements for potential growth and synthesis of new tissue. A robust and unequivocal physiological basis from which to determine N demand is lacking. Yet N dominates plant nutrition. No nutrient is needed in larger quantities and, in most environments, no nutrient is in such limiting supply. Knowledge of the factors governing N demand is essential to predict the needs of crops under a wide range of field situations, so that growers can be given more reliable fertilizer recommendations (Greenwood 1982; van Keulen et al. 1989). This is important, not just for economic reasons, but because of the risks to the environment that can arise from the over-application of N fertilizers, in particular the problem of nitrate leaching (Addiscott et al. 1991).

Lung Density and Lung Mass in Emphysema

Mean lung density (dm) and radiologic (VLx) lung volume can be calculated using CT scan data. As many emphysematous patients are overdistended, the analysis of dm alone could be meaningless. However, lung mass (m) can be calculated as the product of dm and VLx. Twenty-four patients suspected of mild or severe emphysema as judged by roentgenographic and physiologic examinations as well as 16 healthy subjects were included in the protocol. They all underwent both a CT scan of the whole lung and functional tests from which the following were derived: airway resistance, forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC), total lung capacity (TLC), CO transfer capacity, quasi-static compliance at functional residual capacity (FRC), and blood gases. All CT scans were performed at the FRC of each patient. The dm was lower in emphysema patients than in healthy subjects, as m was greater in patients than in healthy subjects; 1,303 +/- 398 g and 997 +/- 133 g, respectively. Although dm values were significantly correlated to FEV1, FEV1/FVC, and TLC, m values were not correlated to any of these functional indices. Unexpectedly, these results show that most patients (22/24) with emphysema have a normal or increased lung mass. Normal or above normal m values might be due to oversecretion in some patients. Nevertheless, the synthesis of new tissue due to chronic inflammation is the most likely explanation that could account for this finding.

A calorimetric system for metabolic studies of newborn babies.

This paper describes a closed circuit calorimetric system designed to determine the amount of energy required for synthesis of new tissue in a newborn baby. This amount can be estimated from the difference between indirect and direct calorimetric measurements. The system allows the simultaneous measurement of oxygen consumption, carbon dioxide production, evaporative water loss and heat loss through convection and radiation in newborn babies under 2.5 kg bodyweight. The babies are exposed to a well defined climate, they can be observed continuously and are fed via a nasogastric tube during the experiment, which may last 24 h or more. Special features of the system are the compensation methods for O2 and CO2 measurements and the double gradient layer for the measurement of dry heat loss. The overall accuracy of the system is of the order of 0.1 W. The value obtained for the energy cost of growth is in close agreement with Hommes' theoretical estimate.

Dark Germination and Seedling Growth in Monocots and Dicots of Different Photosynthetic Efficiencies in 2% and 20.9% O2

The stimulation of net photosynthesis by 1 to 4% 02 in socalled plants is well established and is believed to result from the suppression of photorespiration (16). Growth of Phaseolus vulgaris, Mimulus cardinalis, and the liverwort Marchantia polymorpha increased when aerial portions of the plants were maintained in low 02 compared with ambient air (1, 2). Photosynthesis in the leaves of efficient species is not enhanced by low 02 (4, 9) nor is growth stimulated (1, 2); this is not surprising since these species have either no photorespiration or show quite low rates (5, 14). The assumption is widely held that respiration suppressed by low 02 or stimulated by higher 02 concentrations is nonessential or wasteful in plants. We asked if this kind of respiration is characteristic of a species throughout development, e.g., during germination and early seedling growth. If this were true we could expect to deduce photosynthetic efficiency of seedlings soon after germination and thus improve the efficiency of screening for efficient plants. Alternatively, we might discover an associated respiration with the same oxygen requirement as photorespiration. Growth in darkness of the embryo of imbibed seeds can occur only if respiration releases energy and produces intermediates for synthesis of new tissue. We tested our hypotheses by observing growth in darkness soon after germination in 2% and 20.9% 02 of seedlings of 28 monocots and dicots classified as inefficient or efficient by photosynthetic characteristics.