Mathematical modeling of cell growth in a 3D scaffold and validation of static and dynamic cultures

Tissue engineering, an immensely important field in contemporary clinical practices, aims at the repair or replacement of damaged tissues. The mathematical model proposed herein shows the distribution and growth of cells in their characteristic time in a 3D scaffold model. This study contributes to the progress of simulation techniques in static and dynamic cultures of bone tissue. Brinkman, nutrient transport, and cell growth equations are brought together to quantify the growth behavior of cells. However, when a static culture is being studied, the Brinkman equation is eliminated. The model was validated by experimental cell culture using 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay and scanning electron microscopy. Then, static and dynamic cultures were compared to assess the cell density and cell distribution in the scaffold. Cell counting after 21 days of cell culture showed that the number of cells increased 42‐fold in static and 53.5‐fold in dynamic cultures, which was in good agreement with our model estimations (37‐fold increase in the number of cells in static and 49‐fold increase in dynamic cultures). In conclusion, our mathematical model could predict cell distribution and growth in the scaffold.     

Two clusters of charged residues located in the electropositive face of the von Willebrand factor A1 domain are essential for heparin binding

The VWF A1 domain seems to possess two heparin binding regions (residues 565-587 and 633-648) displaying positively charged amino acids, but the overall polyanion-A1 domain interaction scheme remains essentially elusive. To probe this molecular reaction as well as the role of electrostatic forces in VWF-heparin interaction, we performed mutagenesis and molecular modeling experiments. Fifteen mutated rVWFs were expressed [R571A, K572A, R573A, K585A, R571A/K572A/R573A, R578A/R579A, R578A/R579A/K585A, R571A/K572A/R573A/R578A/R579A/K585A (6A), K642G, K643G, K644G, K645G, K642G/K645G, K643G/K644G, and K642G/K643G/K644G/K645G (4G)]. Experimental results indicate that the multimeric structure of the mutants was similar to that of wild-type (WT) rVWF and that all rVWFs displayed normal binding to four conformation-dependent mAbs directed against the A1 domain. Three variants displayed significant reductions in the level of heparin binding. The 6A variant showed 39.2 +/- 1.3% of the WT rVWF level (p < 0.005), while mutants K643G/K644G and 4G showed 63.6 +/- 3.2 and 53.3 +/- 5% of the WT rVWF level, respectively (p < 0.005). Computational investigations showed that one face of the A1 domain is strongly electropositive, indicating that electrostatic forces should be essential in steering heparin onto its binding site. In agreement with our experimental data, the most striking alterations of the electrostatic potential contours were seen for mutants 4G, K643G/K644G, and 6A. Our data suggest that two clusters, one at positions 571-573, 578, 579, and 585 and the other at positions 642-645, act in concert for the recognition of heparin, forming a single extended binding surface across the electropositive face of the VWF A1 domain. A structural model of the VWF A1 domain-heparin complex is proposed, taking into account both experimental and computer modeling data.     

Effect of elevated dissolved carbon dioxide concentrations on growth of Corynebacterium glutamicum on D-glucose and L-lactate

The effect of increased dissolved carbon dioxide concentrations on growth of Corynebacterium glutamicum was studied with continuous turbidostatic cultures. The carbon sources were either l-lactate or d-glucose. To increase the dissolved carbon dioxide concentration the carbon dioxide partial pressure of the inlet gas stream pCO2,IN was increased stepwise from 0.0003 bar (air) up to 0.79 bar, while the oxygen partial pressure of the inlet gas stream was kept constant at 0.21 bar. For each resulting carbon dioxide partial pressure pCO2 the maximum specific growth rate mu(max) was determined from the feed rate resulting from the turbidostatic control. On d-glucose and pCO2 up to 0.26 bar, mu(max) was mostly constant around 0.58 h(-1). Higher pCO2 led to a slight decrease of mu(max). On l-lactate mu(max) increased gradually with increasing carbon dioxide partial pressures from 0.37 h(-1) under aeration with air to a maximum value of 0.47 h(-1) at a pCO2 of 0.26 bar. At very high pCO2 (0.81 bar) mu(max) decreased down to 0.35 h(-1) independent of the carbon source.     

Dex-ras1 and Serum- and Glucocorticoid-inducible Protein Kinase 1: Regulation of Expression by Dexamethasone in HEK293 Cells

The molecular and cellular basis of the psychotropic actions of adrenal corticosteroids is poorly understood. Previously, we reported that modulation of large conductance Ca²⁺-activated potassium channel (BK-channel) function by glucocorticoids can be recapitulated in human embryonic kidney293 (HEK293) cells (J Physiol 537:57, 2001). In the present paper, we examined the effect of dexamethasone on the expression of candidate mediator proteins of glucocorticoid action, dex-ras1 and serum and glucocorticoid inducible protein kinase 1 (SGK), in HEK293 cells. Dex-ras1 mRNA was readily detectable under basal conditions however, no changes of dex-ras1 mRNA expression occurred upon exposure to 100 nM of dexamethasone for 2 h. In contrast, a 2.5-fold increase of SGK mRNA was found under similar conditions. Total levels of cellular SGK protein were unaltered upon exposure to dexamethasone, but a marked increase of SGK in a Triton-X100 insoluble fraction was observed. BK-channel α-subunits could not be co-immunoprecipitated with SGK. In summary, SGK, but not dex-ras1, mRNA is rapidly induced by glucocorticoid stimulation in HEK293 cells. However, there appears to be no direct protein-protein interaction between SGK and BK-channel α-subunits. Presented to mark the 70th birthday of Professor George Fink. Special issue article in honor of George Fink.     

Response of vegetation phenology to urbanization in the conterminous United States

The influence of urbanization on vegetation phenology is gaining considerable attention due to its implications for human health, cycling of carbon and other nutrients in Earth system. In this study, we examined the relationship between change in vegetation phenology and urban size, an indicator of urbanization, for the conterminous United States. We studied more than 4500 urban clusters of varying size to determine the impact of urbanization on plant phenology, with the aids of remotely sensed observations since 2003–2012. We found that phenology cycle (changes in vegetation greenness) in urban areas starts earlier (start of season, SOS) and ends later (end of season, EOS), resulting in a longer growing season length (GSL), when compared to the respective surrounding urban areas. The average difference of GSL between urban and rural areas over all vegetation types, considered in this study, is about 9 days. Also, the extended GSL in urban area is consistent among different climate zones in the United States, whereas their magnitudes are varying across regions. We found that a tenfold increase in urban size could result in an earlier SOS of about 1.3 days and a later EOS of around 2.4 days. As a result, the GSL could be extended by approximately 3.6 days with a range of 1.6–6.5 days for 25th ~ 75th quantiles, with a median value of about 2.1 days. For different vegetation types, the phenology response to urbanization, as defined by GSL, ranges from 1 to 4 days. The quantitative relationship between phenology and urbanization is of great use for developing improved models of vegetation phenology dynamics under future urbanization, and for developing change indicators to assess the impacts of urbanization on vegetation phenology.     

Cell-to-Cell Spread of the RNA Interference Response Suppresses Semliki Forest Virus (SFV) Infection of Mosquito Cell Cultures and Cannot Be Antagonized by SFV

In their vertebrate hosts, arboviruses such as Semliki Forest virus (SFV) (Togaviridae) generally counteract innate defenses and trigger cell death. In contrast, in mosquito cells, following an early phase of efficient virus production, a persistent infection with low levels of virus production is established. Whether arboviruses counteract RNA interference (RNAi), which provides an important antiviral defense system in mosquitoes, is an important question. Here we show that in Aedes albopictus-derived mosquito cells, SFV cannot prevent the establishment of an antiviral RNAi response or prevent the spread of protective antiviral double-stranded RNA/small interfering RNA (siRNA) from cell to cell, which can inhibit the replication of incoming virus. The expression of tombusvirus siRNA-binding protein p19 by SFV strongly enhanced virus spread between cultured cells rather than virus replication in initially infected cells. Our results indicate that the spread of the RNAi signal contributes to limiting virus dissemination.In animals, RNA interference (RNAi) was first described for Caenorhabditis elegans (27). The production or introduction of double-stranded RNA (dsRNA) in cells leads to the degradation of mRNAs containing homologous sequences by sequence-specific cleavage of mRNAs. Central to RNAi is the production of 21- to 26-nucleotide small interfering RNAs (siRNAs) from dsRNA and the assembly of an RNA-induced silencing complex (RISC), followed by the degradation of the target mRNA (23, 84). RNAi is a known antiviral strategy of plants (3, 53) and insects (21, 39, 51). Study of Drosophila melanogaster in particular has given important insights into RNAi responses against pathogenic viruses and viral RNAi inhibitors (31, 54, 83, 86, 91). RNAi is well characterized for Drosophila, and orthologs of antiviral RNAi genes have been found in Aedes and Culex spp. (13, 63).Arboviruses, or arthropod-borne viruses, are RNA viruses mainly of the families Bunyaviridae, Flaviviridae, and Togaviridae. The genus Alphavirus within the family Togaviridae contains several mosquito-borne pathogens: arboviruses such as Chikungunya virus (16) and equine encephalitis viruses (88). Replication of the prototype Sindbis virus and Semliki Forest virus (SFV) is well understood (44, 71, 74, 79). Their genome consists of a positive-stranded RNA with a 5′ cap and a 3′ poly(A) tail. The 5′ two-thirds encodes the nonstructural polyprotein P1234, which is cleaved into four replicase proteins, nsP1 to nsP4 (47, 58, 60). The structural polyprotein is encoded in the 3′ one-third of the genome and cleaved into capsid and glycoproteins after translation from a subgenomic mRNA (79). Cytoplasmic replication complexes are associated with cellular membranes (71). Viruses mature by budding at the plasma membrane (35).In nature, arboviruses are spread by arthropod vectors (predominantly mosquitoes, ticks, flies, and midges) to vertebrate hosts (87). Little is known about how arthropod cells react to arbovirus infection. In mosquito cell cultures, an acute phase with efficient virus production is generally followed by the establishment of a persistent infection with low levels of virus production (9). This is fundamentally different from the cytolytic events following arbovirus interactions with mammalian cells and pathogenic insect viruses with insect cells. Alphaviruses encode host response antagonists for mammalian cells (2, 7, 34, 38).RNAi has been described for mosquitoes (56) and, when induced before infection, antagonizes arboviruses and their replicons (1, 4, 14, 15, 29, 30, 32, 42, 64, 65). RNAi is also functional in various mosquito cell lines (1, 8, 43, 49, 52). In the absence of RNAi, alphavirus and flavivirus replication and/or dissemination is enhanced in both mosquitoes and Drosophila (14, 17, 31, 45, 72). RNAi inhibitors weakly enhance SFV replicon replication in tick and mosquito cells (5, 33), posing the questions of how, when, and where RNAi interferes with alphavirus infection in mosquito cells.Here we use an A. albopictus-derived mosquito cell line to study RNAi responses to SFV. Using reporter-based assays, we demonstrate that SFV cannot avoid or efficiently inhibit the establishment of an RNAi response. We also demonstrate that the RNAi signal can spread between mosquito cells. SFV cannot inhibit cell-to-cell spread of the RNAi signal, and spread of the virus-induced RNAi signal (dsRNA/siRNA) can inhibit the replication of incoming SFV in neighboring cells. Furthermore, we show that SFV expression of a siRNA-binding protein increases levels of virus replication mainly by enhancing virus spread between cells rather than replication in initially infected cells. Taken together, these findings suggest a novel mechanism, cell-to-cell spread of antiviral dsRNA/siRNA, by which RNAi limits SFV dissemination in mosquito cells.     

Determination of CO₂ sensitivity of micro-organisms in shaken bioreactors. I. Novel method based on the resistance of sterile closure

Influence of carbon dioxide on growth and product kinetics of industrially important micro-organisms is essential for the interpretation of a bioprocess. In this research, the CO? effects on productivity and growth rate of micro-organisms have been studied by using a variety of kplug. The applied method is based on a different concentration of CO? in the headspace of ventilation flasks. The presented method is simple, inexpensive and shows similar results compared to large-scale fermentation regarding the evolution of CO? in a batch system. For the investigation of the proposed method, experiments employing Arxula adeninivorans LS3, Corynebacterium glutamicum (DM1730 and ATCC WT13032) and Hansenula polymorpha DSM70277 as model organisms in the ventilation flasks are performed. The fermentations in the RAMOS (respiratory activity monitoring system) device were carried out with a normal aeration rate (1 vvm) and under the same operating conditions as the ventilation flask f1. The modified unsteady-state model was used to predict the operation conditions of a biological system in the ventilation flasks. In the present study, a novel and easy method for the quantification of CO? sensitivity of micro-organisms in shaken bioreactors (called ventilation flask) was achieved.     

La Crosse bunyavirus nonstructural protein NSs serves to suppress the type I interferon system of mammalian hosts

La Crosse virus (LACV) is a mosquito-transmitted member of the Bunyaviridae family that causes severe encephalitis in children. For the LACV nonstructural protein NSs, previous overexpression studies with mammalian cells had suggested two different functions, namely induction of apoptosis and inhibition of RNA interference (RNAi). Here, we demonstrate that mosquito cells persistently infected with LACV do not undergo apoptosis and mount a specific RNAi response. Recombinant viruses that either express (rLACV) or lack (rLACVdelNSs) the NSs gene similarly persisted and were prone to the RNAi-mediated resistance to superinfection. Furthermore, in mosquito cells overexpressed LACV NSs was unable to inhibit RNAi against Semliki Forest virus. In mammalian cells, however, the rLACVdelNSs mutant virus strongly activated the antiviral type I interferon (IFN) system, whereas rLACV as well as overexpressed NSs suppressed IFN induction. Consequently, rLACVdelNSs was attenuated in IFN-competent mouse embryo fibroblasts and animals but not in systems lacking the type I IFN receptor. In situ analyses of mouse brains demonstrated that wild-type and mutant LACV mainly infect neuronal cells and that NSs is able to suppress IFN induction in the central nervous system. Thus, our data suggest little relevance of the NSs-induced apoptosis or RNAi inhibition for growth or pathogenesis of LACV in the mammalian host and indicate that NSs has no function in the insect vector. Since deletion of the viral NSs gene can be fully complemented by inactivation of the host's IFN system, we propose that the major biological function of NSs is suppression of the mammalian innate immune response.     

Effects of combined therapy with thalidomide and glucantime on leishmaniasis induced by Leishmania major in BALB/c mice

For treating Leishmania major infection in BALB/c mice, we used thalidomide in conjunction with glucantime. Groups of mice were challenged with 510(3) metacyclic promastigotes of L. major subcutaneously. A week after the challenge, drug treatment was started and continued for 12 days. Thalidomide was orally administrated 30 mg/kg/day and glucantime was administrated intraperitoneally (200 mg/kg/day). It was shown that the combined therapy is more effective than single therapies with each one of the drugs since the foot pad swelling in the group of mice received thalidomide and glucantime was significantly decreased (0.9 +/- 0.2 mm) compared to mice treated with either glucantime, thalidomide, or carrier alone (1.2 +/- 0.25, 1.4 +/- 0.3, and 1.7 +/- 0.27 mm, respectively). Cytokine study showed that the effect of thalidomide was not dependent on IL-12; however, it up-regulated IFN-gamma and down-regulated IL-10 production. Conclusively, thalidomide seems promising as a conjunctive therapy with antimony in murine model of visceral leishmaniasis.     

Determination of CO₂ sensitivity of micro-organisms in shaken bioreactors. II. Novel online monitoring method

In the present study, a new online monitoring method for the determination of the CO? sensitivity of micro-organisms, based on the values of the respiration factors [OTR (oxygen transfer rate) and CTR (carbon dioxide transfer rate)], obtained by using the RAMOS (respiratory activity monitoring system) device considering a variety of aeration rates in the measuring flask, is investigated. Based on the data of the OTR, obtained by RAMOS under a variety of specific aeration rates, the proposed new method was developed as an online monitoring method for CO? sensitivity of micro-organisms in shaken bioreactors. A maximum accumulated CO? concentration of 12% was derived in applied methods, provided that the cultivation system is carried out under optimal conditions. Additionally, to predict these conditions, an unsteady-state gas transfer model in shaken bioreactors would be very advantageous. The data of OTR obtained using the RAMOS device were analysed and recalculated by a programme considering the calibration factor (Cf). The major advantage of the new method is the possibility to determine the metabolic activity, regardless of manual sampling.