Cell-Matrix Elastocapillary Interactions Drive Pressure-based Wetting of Cell Aggregates

Cell-matrix interfacial energies and the energies of matrix deformations may be comparable on cellular length-scales, yet how capillary effects influence tis sue shape and motion are unknown. In this work, we induce wetting (spreading and migration) of cell aggregates, as models of active droplets onto adhesive substrates of varying elasticity and correlate the dynamics of wetting to the balance of interfacial tensions. Upon wetting rigid substrates, cell-substrate tension drives outward expansion of the monolayer. By contrast, upon wetting compliant substrates, cell substrate tension is attenuated and aggregate capillary forces contribute to internal pressures that drive expansion. Thus, we show by experiments, data-driven modeling and computational simulations that myosin-driven 'active elasto-capillary' effects enable adaptation of wetting mechanisms to substrate rigidity and introduce a novel, pressure-based mechanism for guiding collective cell motion.

Active Regulation of Pressure and Volume Defines an Energetic Constraint on the Size of Cell Aggregates

We explore the relationship between the nonequilibrium generation of myosin-induced active stress within the F-actin cytoskeleton and the pressure-volume relationship of cellular aggregates as models of simple tissues. We find that due to active stress, aggregate surface tension depends upon its size. As a result, both pressure and cell number density depend on size and violate equilibrium assumptions. However, the relationship between them resembles an equilibrium equation of state with an effective temperature. This suggests that bulk and surface properties of aggregates balance to yield a constant average work performed by each cell on their environment in regulating tissue size. These results describe basic physical principles that govern the size of cell aggregates.

Investigation of the role of the GABRG2 gene variant in migraine

Migraine is the most common neurological disorder worldwide affecting about 12% of the worldwide population. This disorder has been classed into two main types of migraine-with and without aura. While a number of factors can influence the onset of migraine, a major factor is that of genetics. The GABAA gene encodes for the GABAA receptor. Along with other receptors, the GABAA receptor is involved in the mediation of neuronal activities. In this study, a GABRG2 gene (GABAA receptor gamma-2-subunit) SNP (rs211037) was genotyped on a migraine case-control population of 546 (273 affected and an equal number of healthy) individuals. Using specifically designed primers, a high resolution melt (HRM) assay was carried out in the genotyping process. After genotyping, results were compared in the case and control populations. Analysis of results showed no significant differences in the allele frequencies between case and control populations. Similarly no differences were detected for subtypes or for a specific gender of migraine (p>0.05). Although this gene has been previously found to be involved in febrile seizures and there is some co-morbidity between epilepsy and migraine, we decided to investigate this marker for involvement in migraine. The results did not support a role for the tested GABRG2 variant in migraine.

Surface Characterisation of Si After HF Treatments and its Influence on the Dielectric Breakdown of Thermal Oxides

The characteristics of the HF-treated Si-surface are investigated as a function of dipping time in dilute HF solutions. It is found that the contact angle is a very sensitive measure for the degree of oxidation of the Si-surface. The importance of obtaining a perfectly passivated surface in order to reduce the particle deposition on the surface is shown. HF-last cleans are found to be beneficial in terms of metallic contamination and gate oxide integrity. The importance of the loading ambient in furnaces is investigated after HF-treatments and RCA-cleans.

Association study of calcitonin gene-related polypeptide-alpha (CALCA) gene polymorphism with migraine

Migraine is a neurological disorder that is associated with increased levels of calcitonin gene-related peptide (CGRP) in plasma. CGRP, being one of the mediators of neurogenic inflammation and a phenomenon implicated in the pathogenesis of migraine headache, is thus suggested to have an important role in migraine pathophysiology. Polymorphisms of the CALCA gene have been linked to Parkinson's disease, ovarian cancer and essential hypertension, suggesting a functional role for these polymorphisms. Given the strong evidence linking CGRP and migraine, it is hypothesised that polymorphisms in the CALCA gene may play a role in migraine pathogenesis. Seemingly non functional intronic polymorphisms are capable of disrupting normal RNA processing or introducing a splice site in the transcript. A 16bp deletion in the first intron of the CALCA gene has been reported to be a good match for the binding site for a transcription factor expressed strongly in neural crest derived cells, AP-2. This deletion also eliminates an intron splicing enhancer (ISE) that may potentially cause exon skipping. This study investigated the role of the 16bp intronic deletion in the CALCA gene in migraineurs and matched control individuals. Six hundred individuals were genotyped for the deletion by polymerase chain reaction followed by fragment analysis on the 3130 Genetic Analyser. The results of this study showed no significant association between the intronic 16bp deletion in the CALCA gene and migraine in the tested Australian Caucasian population. However, given the evidence linking CGRP and migraine, further investigation of variants with this gene may be warranted.

Divergent roles of NF-κB and Egr-1 in flow-dependent restenosis after angioplasty and stenting

OBJECTIVE

Restenosis after both angioplasty and stenting is flow dependent. The effects of flow are preventable with the antioxidant pyrrolidine dithiocarbamate (PDTC) after angioplasty but not after stenting. We examined to what extent these observations could be explained by the effect of PDTC on NF-κB and Egr-1, two transcription factors which are both flow- and redox-sensitive.

METHODS

In a flow-modified rabbit carotid model of angioplasty and stenting, we assessed the effects of altered flow, injury and PDTC on expression of Egr-1 and nuclear binding activity of NF-κB. We also examined the effects of local delivery of decoy oligodeoxynucleotides (ODN) specific for NF-κB and Egr-1 on morphology at 28 days in normal and low flow.

RESULTS

The activity of both transcription factors was enhanced by injury (stent>balloon alone) and was further augmented by low flow. PDTC markedly attenuated the activity of NF-κB but not Egr-1. Specific decoy ODN for Egr-1 attenuated intima formation in both stented and balloon injured vessels in both normal and low flow but had no effect on remodelling. In contrast while NF-κB decoy ODN caused a modest but significant reduction in intima formation, there was a striking effect on remodelling in low flow vessels only.

CONCLUSIONS

We conclude that Egr-1 plays a pivotal role in intima formation under all flow conditions and that NF-κB plays a key role in flow-sensitive remodelling after angioplasty and that NF-κB inhibition likely accounts for a significant part of the morphological effects of PDTC after vessel injury.

The role of c-jun in PDTC-sensitive flow-dependent restenosis after angioplasty and stenting

Restenosis after balloon angioplasty and stenting is exacerbated by low flow. Flow-dependent restenosis after angioplasty but not stenting is prevented by the antioxidant pyrrolidine dithiocarbamate (PDTC). c-jun may play a role in these events as AP-1 activity is both flow and redox sensitive. Carotid arteries of cholesterol fed rabbits underwent stenting or balloon injury in the presence of low or normal flow. c-jun mRNA expression was enhanced by low flow and injury (stent>balloon) and inhibited by the antioxidant PDTC irrespective of the injury type. The effect of locally delivered DZ13 (a DNAzyme specific for c-jun) or scrambled DZ13 (inactive DNAzyme) was assessed by histomorphometry at 28 days. Low flow significantly increased intimal hyperplasia in B and S relative to normal flow (P<0.05). The active DNAzyme DZ13 markedly reduced intimal hyperplasia (P<0.001) and increased lumen size (P<0.05) in balloon-injured but not in stented segments, and abrogated the effect of low flow on restenosis after angioplasty, similar to the morphological effects of PDTC. We conclude that c-jun expression is enhanced by low flow and by injury (stent>balloon) and markedly attenuated by PDTC, and that c-jun is an important mediator of flow-dependent restenosis in balloon-injured but not stented vessels.

Low flow promotes instent intimal hyperplasia. Comparison with lumen loss in balloon-injured and uninjured vessels and the effects of the antioxidant pyrrolidine dithiocarbamate

Low flow (LF) promotes late lumen loss after angioplasty by exacerbating inward remodelling through redox-sensitive mechanisms. Stents eliminate inward remodelling and the effect of LF on in-stent restenosis is uncertain. We performed over-sized (1.3-1.5:1) stenting (S) and balloon injury (in the same vessel, B) to the carotid arteries of cholesterol-fed rabbits and compared 28-day late lumen loss with that in an uninjured segment in the same vessel (U). Vessels (n = 5 animals per group) were subjected to high (H), normal (N) and low (L) flow in animals fed either vehicle (V) or the antioxidant pyrrolidine dithiocarbamate, PDTC (P). LF significantly increased in-stent neointima formation relative to normal and high flow (SLV 0.72 +/- 0.07 mm(2) versus SNV 0.43 +/- 0.08 mm(2) versus SHV 0.28 +/- 0.04 mm(2), P < 0.05). However, LF resulted in greater lumen loss in segments from the same vessel subject to balloon injury (lumen SLV 5.18 +/- 0.40 mm(2) and SNV 5.32 +/- 0.40 mm(2) versus BLV 1.28 +/- 0.33 mm(2) and BNV 2.19 +/- 0.28 mm(2)), by greater enhancement of inward remodelling. In addition, inward remodelling and lumen loss due to LF were greater in balloon-injured segments than in adjacent uninjured segments where shear homeostatic remodelling occurs (lumen BLV 1.28 +/- 0.33 mm(2) versus ULV 1.52 +/- 0.22 mm(2)). Lastly, while PDTC effectively reduced intima formation and inward remodelling due to LF in balloon-injured vessels there was no effect on flow-dependent neointima formation in stented vessels. We conclude that LF accentuates in-stent neointima formation, but that flow-dependent lumen loss after stenting is less than that after balloon injury. When LF is present lumen loss can be minimised by antioxidants or stenting.

A novel system for assigning the mode of inheritance in mitochondrial disorders using cybrids and rhodamine 6G

When normal human cultured skin fibroblasts were treated with the fluorescent dye rhodamine 6G (R6G), there was a drastic reduction in numbers of intact mitochondria and electron transport chain enzyme activities, despite the fact that mitochondrial DNA (mtDNA) was still present in treated cells. We used this observation to develop a novel system for generating cybrids. When cultured skin fibroblast cells from a patient with the mitochondrial encephalopathy and ragged-red fibers (MERRF) syndrome harboring the A8344G mtDNA mutation and which showed a severe reduction in cytochrome c oxidase activity were treated with R6G and fused to enucleated HeLaCOT cells, the resulting cybrid clones showed recovery of cytochrome c oxidase activity, and were shown to have mtDNA derived solely from the HeLaCOT cell line. R6G has significant advantages over ethidium bromide in removing the mitochondrial elements from cultured cells, and the results reported here demonstrate that this strategy can be used to determine the origin of the genetic defect in patients with electron transport chain abnormalities.

Methylmalonyl-CoA mutase induction by cerebral ischemia and neurotoxicity of the mitochondrial toxin methylmalonic acid

Differential screening of gerbil brain hippocampal cDNA libraries was used to search for genes expressed in ischemic, but not normal, brain. The methylmalonyl-CoA mutase (MCM) cDNA was highly expressed after ischemia and showed a 95% similarity to mouse and 91% similarity to the human MCM cDNAs. Transient global ischemia induced a fourfold increase in MCM mRNA on Northern blots from both hippocampus and whole forebrain. MCM protein exhibited a similar induction on Western blots of gerbil cerebral cortex 8 and 24 hr after ischemia. Treatment of primary brain astrocytes with either the branched-chain amino acid (BCAA) isoleucine or the BCAA metabolite, propionate, induced MCM mRNA fourfold. Increased concentrations of BCAAs and odd-chain fatty acids, both of which are metabolized to propionate, may contribute to inducing the MCM gene during ischemia. Methylmalonic acid, which is formed from the MCM substrate methylmalonyl-CoA and which inhibits succinate dehydrogenase (SDH), produced dose-related cell death when injected into the basal ganglia of adult rat brain. This neurotoxicity is similar to that of structurally related mitochondrial SDH inhibitors, malonate and 3-nitropropionic acid. Methylmalonic acid may contribute to neuronal injury in human conditions in which it accumulates, including MCM mutations and B12 deficiency. This study shows that methylmalonyl-CoA mutase is induced by several stresses, including ischemia, and would serve to decrease the accumulation of an endogenous cellular mitochondrial inhibitor and neurotoxin, methylmalonic acid.