Apoptosis- and necrosis-induced changes in light attenuation measured by optical coherence tomography

Optical coherence tomography (OCT) was used to determine optical properties of pelleted human fibroblasts in which necrosis or apoptosis had been induced. We analysed the OCT data, including both the scattering properties of the medium and the axial point spread function of the OCT system. The optical attenuation coefficient in necrotic cells decreased from 2.2 ± 0.3 mm−1 to 1.3 ± 0.6 mm−1, whereas, in the apoptotic cells, an increase to 6.4 ± 1.7 mm−1 was observed. The results from cultured cells, as presented in this study, indicate the ability of OCT to detect and differentiate between viable, apoptotic, and necrotic cells, based on their attenuation coefficient. This functional supplement to high-resolution OCT imaging can be of great clinical benefit, enabling on-line monitoring of tissues, e.g. for feedback in cancer treatment

HtrA2/Omi Terminates Cytomegalovirus Infection and Is Controlled by the Viral Mitochondrial Inhibitor of Apoptosis (vMIA)

Viruses encode suppressors of cell death to block intrinsic and extrinsic host-initiated death pathways that reduce viral yield as well as control the termination of infection. Cytomegalovirus (CMV) infection terminates by a caspase-independent cell fragmentation process after an extended period of continuous virus production. The viral mitochondria-localized inhibitor of apoptosis (vMIA; a product of the UL37x1 gene) controls this fragmentation process. UL37x1 mutant virus-infected cells fragment three to four days earlier than cells infected with wt virus. Here, we demonstrate that infected cell death is dependent on serine proteases. We identify mitochondrial serine protease HtrA2/Omi as the initiator of this caspase-independent death pathway. Infected fibroblasts develop susceptibility to death as levels of mitochondria-resident HtrA2/Omi protease increase. Cell death is suppressed by the serine protease inhibitor TLCK as well as by the HtrA2-specific inhibitor UCF-101. Experimental overexpression of HtrA2/Omi, but not a catalytic site mutant of the enzyme, sensitizes infected cells to death that can be blocked by vMIA or protease inhibitors. Uninfected cells are completely resistant to HtrA2/Omi induced death. Thus, in addition to suppression of apoptosis and autophagy, vMIA naturally controls a novel serine protease-dependent CMV-infected cell-specific programmed cell death (cmvPCD) pathway that terminates the CMV replication cycle

Tailoring Stimuli Responsiveness using Dynamic Covalent Cross-Linking of Poly(vinyl alcohol)-Heparin Hydrogels for Controlled Cell and Growth Factor Delivery

Heparin-based hydrogels are attractive for cell encapsulation and drug delivery because of the ability of heparin to bind native proteins. However, heparin-based hydrogels have received little attention for their potential as stimuli-sensitive materials. Biosynthetic, poly(vinyl alcohol) (PVA)-heparin hydrogels were formed using dynamic, covalent cross-linking. Hydrogel stimuli-sensitivity was tailored by tuning the concentration of heparin to PVA. Relatively thermally and pH stable hydrogels were produced when formed from only the synthetic, nonionic PVA polymer cross-linked via hydrazone bonds. Cross-linking in the ionic biopolymer heparin, to form PVA-heparin gels, has a profound impact on thermal stability, with degradation ranging from over 6 months to only 4 days across 25-50°C. PVA-heparin hydrogels degrade within 18 days at basic pH (10), while not fully degrading over 6 months at lower pH (4, 7.4). This finding is attributed to the anionic repulsion of carboxyls and sulfates in heparin. PVA-heparin macromers were cytocompatible and enabled mild cell encapsulation, in addition to providing pH-controlled growth factor release. Overall, it is demonstrated that the biopolymer heparin can be used to create pH and temperature-responsive hydrogel biomaterials for cell and drug delivery

The role of algal organic matter in the separation of algae and cyanobacteria using the novel “Posi” - Dissolved air flotation process

Algae and cyanobacteria frequently require separation from liquid media in both water treatment and algae culturing for biotechnology applications. The effectiveness of cell separation using a novel dissolved air flotation process that incorporates positively charged bubbles (PosiDAF) has recently been of interest but has been shown to be dependent on the algae or cyanobacteria species tested. Previously, it was hypothesised that algal organic matter (AOM) could be impacting the separation efficiency. Hence, this study investigates the influence of AOM on cell separation using PosiDAF, in which bubbles are modified using a commercially available cationic polyelectrolyte poly(N, N-diallyl-N,N-dimethylammonium chloride) (PDADMAC). The separation of Chlorella vulgaris CS-42/7, Mychonastes homosphaera CS-556/01 and two strains of Microcystis aeruginosa (CS-564/01 and CS-555/1), all of which have similar cell morphology but different AOM character, was investigated. By testing the cell separation in the presence and absence of AOM, it was determined that AOM enhanced cell separation for all the strains but to different extents depending on the quantity and composition of carbohydrates and proteins in the AOM. By extracting AOM from the strain for which optimal separation was observed and adding it to the others, cell separation improved from 90%. This was attributed to elevated levels of acidic carbohydrates as well as glycoprotein-carbohydrate conjugations, which in turn were related to the nature and quantity of proteins and carbohydrates present in the AOM. Therefore, it was concluded that process optimisation requires an in-depth understanding of the AOM and its components. If culturing algae for biotechnology applications, this indicates that strain selection is not only important with respect to high value product content, but also for cell separation