The effects of inhibition and siRNA knockdown of collagen-binding integrins on human umbilical vein endothelial cell migration and tube formation

Blood vessels in the body are lined with endothelial cells which have vital roles in numerous physiological and pathological processes. Collagens are major constituents of the extracellular matrix, and many adherent cells express several collagen-binding adhesion receptors. Here, we study the endothelium-collagen interactions mediated by the collagen-binding integrins, α1β1, α2β1, α10β1 and α11β1 expressed in human umbilical vein endothelial cells (HUVECs). Using qPCR, we found expression of the α10 transcript of the chondrocyte integrin, α10β1, along with the more abundant α2, and low-level expression of α1. The α11 transcript was not detected. Inhibition or siRNA knockdown of the α2-subunit resulted in impaired HUVEC adhesion, spreading and migration on collagen-coated surfaces, whereas inhibition or siRNA knockdown of α1 had no effect on these processes. In tube formation assays, inhibition of either α1 or α2 subunits impaired the network complexity, whereas siRNA knockdown of these integrins had no such effect. Knockdown of α10 had no effect on cell spreading, migration or tube formation in these conditions. Overall, our results indicate that the collagen-binding integrins, α1β1 and α2β1 play a central role in endothelial cell motility and self-organisation.

Selectivity of the collagen-binding integrin inhibitors, TC-I-15 and obtustatin

Integrins are a family of 24 adhesion receptors which are both widely-expressed and important in many pathophysiological cellular processes, from embryonic development to cancer metastasis. Hence, integrin inhibitors are valuable research tools which may have promising therapeutic uses. Here, we focus on the four collagen-binding integrins α1β1, α2β1, α10β1 and α11β1. TC-I-15 is a small molecule inhibitor of α2β1 that inhibits platelet adhesion to collagen and thrombus deposition, and obtustatin is an α1β1-specific disintegrin that inhibits angiogenesis. Both inhibitors were applied in cellular adhesion studies, using synthetic collagen peptide coatings with selective affinity for the different collagen-binding integrins and testing the adhesion of C2C12 cells transfected with each. Obtustatin was found to be specific for α1β1, as described, whereas TC-I-15 is shown to be non-specific, since it inhibits both α1β1 and α11β1 as well as α2β1. TC-I-15 was 100-fold more potent against α2β1 binding to a lower-affinity collagen peptide, suggestive of a competitive mechanism. These results caution against the use of integrin inhibitors in a therapeutic or research setting without testing for cross-reactivity.

Collagen scaffolds functionalized with triple-helical peptides support 3D HUVEC culture

Porous biomaterials which provide a structural and biological support for cells have immense potential in tissue engineering and cell-based therapies for tissue repair. Collagen biomaterials that can host endothelial cells represent promising tools for the vascularization of engineered tissues. Three-dimensional collagen scaffolds possessing controlled architecture and mechanical stiffness are obtained through freeze–drying of collagen suspensions, followed by chemical cross-linking which maintains their stability. However, cross-linking scaffolds renders their biological activity suboptimal for many cell types, including human umbilical vein endothelial cells (HUVECs), by inhibiting cell–collagen interactions. Here, we have improved crucial HUVEC interactions with such cross-linked collagen biomaterials by covalently coupling combinations of triple-helical peptides (THPs). These are ligands for collagen-binding cell-surface receptors (integrins or discoidin domain receptors) or secreted proteins (SPARC and von Willebrand factor). THPs enhanced HUVEC adhesion, spreading and proliferation on 2D collagen films. THPs grafted to 3D-cross-linked collagen scaffolds promoted cell survival over seven days. This study demonstrates that THP-functionalized collagen scaffolds are promising candidates for hosting endothelial cells with potential for the production of vascularized engineered tissues in regenerative medicine applications.

Coupling of a specific photoreactive triple-helical peptide to crosslinked collagen films restores binding and activation of DDR2 and VWF

Collagen-based scaffolds may require chemical crosslinking to achieve mechanical properties suitable for tissue engineering. Carbodiimide treatment, often used for this purpose, consumes amino acid side chains required for receptor recognition, thus reducing cell-collagen interaction. Here, we restore recognition and function of both von Willebrand Factor (VWF) and Discoidin Domain Receptor 2 (DDR2) to crosslinked collagen films by derivatisation with a specific triple-helical peptide (THP), an approach previously applied to integrin-mediated cellular adhesion. The THP contained the collagen III-derived active sequence, GPRGQOGVNleGFO, conjugated to a photoreactive moiety, diazirine, allowing UV-dependent covalent coupling to collagen films. Crosslinking of collagen films attenuated the binding of recombinant VWF A3 domain and of DDR2 (as the GST and Fc fusions, respectively), and coupling of the specific THP restored their attachment. These derivatised films supported activation of DDR2 expressed in either COS-7 or HEK293 cells, reflected by phosphorylation of tyrosine 740, and VWF-mediated platelet deposition from flowing blood was restored. Further, such films were able to increase low-density lipoprotein uptake in vascular endothelial cells, a marker for endothelial phenotype. Thus, covalent linkage of specific THPs to crosslinked collagen films i) restores their cognate protein binding, ii) triggers the corresponding cellular responses, and iii) demonstrates the broad applicability of the approach to a range of receptors for applications in regenerative medicine.

Unique charge-dependent constraint on collagen recognition by integrin α10β1

The collagen-binding integrins recognise collagen through their inserted (I) domain, where co-ordination of a Mg^2 + ion in the metal ion-dependent site is reorganised by ligation by a collagen glutamate residue found in specific collagen hexapeptide motifs. Here we show that GROGER, found in the N-terminal domain of collagens I and III, is only weakly recognised by α10β1, an important collagen receptor on chondrocytes, contrasting with the other collagen-binding integrins. Alignment of I domain sequence and molecular modelling revealed a clash between a unique arginine residue (R215) in α10β1 and the positively-charged GROGER. Replacement of R215 with glutamine restored binding. Substituting arginine at the equivalent locus (Q214) in integrins α1 and α2 I domains impaired their binding to GROGER. Collagen II, abundant in cartilage, lacks GROGER. GRSGET is uniquely expressed in the C-terminus of collagen II, but this motif is similarly not recognised by α10β1. These data suggest an evolutionary imperative to maintain accessibility of the terminal domains of collagen II in tissues such as cartilage, perhaps during endochondral ossification, where α10β1 is the main collagen-binding integrin.

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Integrin α10β1 binding to collagen is mapped onto Collagen Toolkits.

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Charged residue in α10 I domain clashes with some binding sites that are unique to collagen II.

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Mutant constructs of other integrin I domains mimic this charge effect.

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Implications for evolution of collagens and cartilage with reference to bone formation

The relationship between tail biting in pigs, docking procedure and other management practices

The tail length (docked, tipped or undocked) and tail status (bitten or unbitten) of 27,870 pigs from 450 units was recorded at six UK abattoirs. A farm survey of the final finishing stage was used to investigate the relationship between management practice and tail biting. This showed that docking was the most important factor influencing the probability of being not bitten, with 2.4% of docked and 8.5% of long-tailed pigs being tail-bitten. The following factors reduced the probability of long-tailed pigs being tail-bitten; light straw provision, use of natural ventilation or artificially controlled natural ventilation (ACNV), mixed sex grouping, meal or liquid feeding, and use of double or multi-space feeders. Docked and long-tailed pigs provided with light straw and natural ventilation/ACNV had levels of tail biting of 1.2% and 4.3% respectively; 3.9% of docked pigs with artificial ventilation and no straw were tail-bitten. Long-tailed pigs fed via double or multi-space feeders also had 3.9% of tails bitten.

Gastric ulcers in finishing pigs: their prevalence and failure to influence growth rate

In an abattoir survey the stomachs of 1242 pigs from 15 farms were examined. Ulceration of the pars oesophagea was present in 22.95 per cent with a range from 4.7 to 57.4 per cent. The ulcers were graded mild in 9.5 per cent and severe in 13.4 per cent of the stomachs. Bile staining and hyperkeratinisation of the pars were significantly more common in stomachs with ulcers than in those without (P < 0.001), although the difference between the hyperkeratinisation in cases with severe ulcers and cases without ulcers was not significant. The daily liveweight gains of 208 males and 150 females from two units with a high prevalence of ulcers were calculated from their weaning weights at about five weeks of age and their slaughter weights at around 90 kg. At the abattoir their stomachs were examined for the presence of ulcers of the pars. The daily liveweight gain of the males was significantly greater than that of the females (P < 0.001), but the presence of mild or severe ulcers had no influence on the rate of gain of the pigs from either unit. The prevalence of ulcers in the males and females was 57.2 and 49.3 per cent, respectively, but the difference was not significant.

Abattoir observations of the weights of stomachs and their contents in pigs slaughtered at known times after their last feed

From 15 farms, 1242 pigs (range per farm 12-169) were sent for slaughter at known times after their last feed. The time of feeding, quantity and type of last feed, time of loading, time in transit, distance travelled, time in lairage and time of slaughter, were recorded. The mean +/- SD stomach weight and wet stomach contents weight were 0.68 +/- 0.12 and 0.55 +/- 0.45 kg, respectively. There were 148 stomachs (11.9%) with wet contents weights > 1 kg, nine > 2 kg but < 3 kg, and one weighed 3.04 kg. The means and ranges for times from last feed to loading interval, time in transport, and time in lairage were 13.6 (0-40), 3.1 (0.75-6.0) and 4.1 (2.1-12.5) h, respectively. The mean and range for distance travelled was 193.1 (43-320) km. Ten stomachs were collected at random from a further load of pigs from one farm. They had been fed 0.64 kg dry pellets and were slaughtered 18.5 h later. The mean and range for wet stomach contents weight was 0.87 kg (0.24-1.33). Samples were dehydrated and the mean calculated stomach dry matter content for the 10 pigs was 127.4 +/- 69.1 g.

Pig welfare and carcase quality: a comparison of the influence of slaughter handling systems at two abattoirs

Pigs from four farms (two producing 'easy' and two 'difficult to handle' pigs) were slaughtered at two abattoirs, each with two slaughter handling systems, so that 25 pigs of each behavioural type were slaughtered by all four handling systems on each day; there were 16 replicates (3200 pigs) in total. The pigs at abattoir X were electrically stunned, either in a floor pen holding five pigs or in a race-restrainer. At abattoir Y the pigs were stunned either in a floor pen holding five pigs or in a dip-lift carbon dioxide stunner. The following measurements were made: hot carcase weight and backfat thickness at P2, degree of rigor mortis 35 minutes post mortem, skin blemish, pH and muscle reflectance in the m longissimus dorsi at 60 minutes and 18 hours post mortem, and pH and muscle reflectance in the m adductor at 18 hours post mortem. At abattoir X, the pigs slaughtered in the race-restrainer had heavier carcases (74.0 kg vs 73.0 kg, P < 0.05), developed rigor mortis more rapidly (8.1 mm vs 7.3 mm, P < 0.01), had more skin blemish (2.8 vs 2.7, P < 0.01), paler m longissimus dorsi muscles after one hour (15.7 vs 13.9, P < 0.01) and 18 hours (27.8 vs 26.6, P < 0.05), and paler m adductor muscles (24.5 vs 22.7, P < 0.001) after 18 hours. At abattoir Y, the pigs handled through the floor pen system had more skin blemish (2.7 vs 2.6, P < 0.05) and a tendency to develop rigor mortis more quickly (6.11 vs 5.32, P = 0.089).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of abattoir and slaughter handling systems on stress indicators in pig blood

Pigs from four farms were slaughtered at two abattoirs, each with two slaughter handling systems. Pigs at abattoir X were electrically stunned, either in a floor pen holding five pigs or in a race-restrainer. At abattoir Y pigs were stunned either in a floor pen holding five pigs or in a dip-lift carbon dioxide stunner. At exsanguination, 96 blood samples (24/farm) were collected from pigs slaughtered through each slaughter handling system (384 samples in total). Serum samples were analysed for cortisol, creatine phosphokinase (CPK) lactate dehydrogenase (LDH) and LDH-isoenzymes. There were no significant differences between the systems at abattoir X. At abattoir Y, pigs slaughtered through the floor pen system had higher levels of LDH-5 (39.84 +/- 1.39 per cent of total LDH vs 34.76 +/- 1.21 per cent, P < 0.05) indicating greater skeletal muscle damage in the floor pen. Pigs at abattoir Y had higher mean serum levels of CPK than pigs at abattoir X (3.63 log10 U/litre vs 3.41 log10 U/litre, 0.03 sed, P < 0.001), higher total LDH activities (1269.5 U/litre vs 922.8 U/litre, P < 0.001) and higher cortisol concentrations (1.70 log10 ng/ml vs 1.51 log10 ng/ml, P < 0.001). These differences suggested that the levels of physical and psychological stress were higher at abattoir Y.