Reductionist in vitro model systems which mimic specific extracellular matrix functions in a highly controlled manner, termed artificial extracellular matrices (aECM), have increasingly been used to elucidate the role of cell-ECM interactions in regulating cell fate. To better understand the interplay of biophysical and biochemical effectors in controlling three-dimensional cell migration, a poly(ethylene glycol)-based aECM platform was used in this study to explore the influence of matrix cross-linking density, represented here by stiffness, on cell migration in vitro and in vivo. In vitro, the migration behavior of single preosteoblastic cells within hydrogels of varying stiffness and susceptibilities to degradation by matrix metalloproteases was assessed by time-lapse microscopy. Migration behavior was seen to be strongly dependent on matrix stiffness, with two regimes identified: a nonproteolytic migration mode dominating at relatively low matrix stiffness and proteolytic migration at higher stiffness. Subsequent in vivo experiments revealed a similar stiffness dependence of matrix remodeling, albeit less sensitive to the matrix metalloprotease sensitivity. Therefore, our aECM model system is well suited to unveil the role of biophysical and biochemical determinants of physiologically relevant cell migration phenomena.
Previous studies have shown that singlestranded RNA (ssRNA) mixed with protamine forms particles and activates immune cells through Toll-like receptors (TLRs). We have found that the size of protamine-RNA particles generated depends on the electrolyte content when mixing the 2 components. Moreover, we have evidenced that (1) nanometric particles induce production of interferon-␣, whereas (2) micrometric particles mainly induce production of tumor necrosis factor-␣ (TNF-␣) in human immune cells. We found that the mechanisms underlying these observations are (1) nanoparticles but not microparticles are selectively phagocytosed by plasmacytoid dendritic cells (pDCs), which produce interferon-␣ and (2) monocytes that produce TNF-␣ have a higher activation threshold than that of pDCs. Thus, at the same time as sensing pathogen-associated molecular patterns such as ssRNA, the immune system distinguishes the size of the associated structure in such a way as to trigger the adapted antivirus (
Polycationic molecules form condensates with DNA and are used for gene therapy as an alternative to viral vectors. As clinical efficacy corresponds to cellular uptake, intracellular stability of the condensates, and bioavailability of the DNA, it is crucial to analyze uptake mechanisms and trafficking pathways. Here, a detailed study of uptake, stability, and localization of PLL-g-PEG-DNA nanoparticles within COS-7 cells is presented, using FACS analysis to assess the involvement of different uptake mechanisms, colocalization studies with markers indicative for different endocytotic pathways, and immunofluorescence staining to analyze colocalization with intracellular compartments. PLL-g-PEG-DNA nanoparticles were internalized in an energy-dependent manner after 2 h and accumulated in the perinuclear region after >6 h. The nanoparticles were found to be stable within the cytoplasm for at least 24 h and did not colocalize with the endosomal pathway. Nanoparticle uptake was approximately 50% inhibited by genistein, an inhibitor of the caveolae-mediated pathway. However, genistein did not inhibit gene expression, and PLL-g-PEG-DNA nanoparticles were not colocalized with caveolin-1 indicating that caveolae-mediated endocytosis is not decisive for DNA delivery. Clathrin-mediated endocytosis and macropinocytosis pathways were reduced by 17 and 24%, respectively, in the presence of the respective inhibitors. When cells were transfected in the presence of double and triple inhibitors, transfection efficiencies were increasingly reduced by 40 and 70%, respectively; however, no differences were found between the different uptake mechanisms. These findings suggest that PLL-g-PEG-DNA nanoparticles enter by several pathways and might therefore be an efficient and versatile tool to deliver therapeutic DNA.
The function of the liver is well-preserved during the aging process, although some evidence suggests that liver regeneration might be impaired with advanced age. We observed a decreased ability of the liver to restore normal volume after partial hepatectomy in elderly mice, and we identified a pathway that rescued regeneration and was triggered by serotonin. 2,5-dimethoxy-4-iodoamphetamine (DOI), a serotonin receptor agonist, reversed the age-related pseudocapillarization of old liver and improved hepatosinusoidal blood flow. After hepatectomy, the open fenestrae were associated with a restored attachment of platelets to endothelium and the initiation of a normal regenerative response, including the up-regulation of essential growth mediators and serotonin receptors. In turn, hepatocyte proliferation recovered along with regain of liver volume and animal survival. DOI operates through the release of VEGF, and its effects could be blocked with anti-VEGF antibodies both in vitro and in vivo. These results suggest that pseudocapillarization in the aged acts as a barrier to liver regeneration. DOI breaks this restraint through an endothelium-dependent mechanism driven by VEGF. This pathway highlights a target for reversing the age-associated decline in the capacity of the liver to regenerate.aging liver | fenestrations | sinusoidal microperfusion T he most significant limiting factor for survival after liver surgery and transplantation of a partial graft is the ability of the remnant liver to regenerate (1-3), as documented in human (4, 5) and several animal models (6-8). Although in young patients, small remnant livers (up to 25% of the normal size) can regenerate fully within a few weeks, this process is impaired in the diseased (9, 10) and possibly, older (11) livers.Conventional histological examination of the liver hardly differs between young and old individuals, although a few features have been identified. For example, the size of the liver and the sinusoidal flow decrease with age, akin to the energy stores (glycogen and ATP in hepatocytes) (12-16). It is well-known that there is an age-associated decline in the clearance of a number of drugs (17-19). We have recently shown that protective strategies during liver surgery, such as ischemic preconditioning, are lost in patients older than 65 y of age (14,20,21).Impaired hepatocyte proliferation was also documented in old mice after major hepatectomy, but the impact on animal survival and underlying mechanisms was not evaluated (22). Finally, a study from Japan in recipients of partial grafts showed a lower liver volume 1 wk after transplantation in patients receiving a graft from donors older than 50 y of age (23). Advanced age is also associated with ultrastructural changes in the hepatic sinusoid, called pseudocapillarization, which includes the defenestration (reduction of porosity) and thickening of the sinusoidal endothelium (24-26). Similar findings for the defenestration and capillarization of the hepatic sinusoidal endothelium have been observed in t...
Polyelectrolyte multilayer coatings have emerged as substrates to control cellular behavior, but interactions with human multipotent mesenchymal stromal cells (MSCs) have not been studied. We looked at layer-by-layer coatings of cationic poly-L-lysine (PLL) and anionic hyaluronic acid (HA) as substrates for MSCs of placenta and adipose tissue. This system allows for modulation of thickness (number of deposition cycles), stiffness (chemical cross-linking of bulk layer), and adhesiveness (fibronectin (FN) interface). Native, as-built PLL/HA multilayer coatings were poorly adhesive for MSCs despite spectroscopy-confirmed high surface density of pre-adsorbed FN. Stratification of cross-linked PLL/HA multilayers of different stiffnesses revealed that multilayers modified with a high cross-linking regimen became efficient substrates for MSC adhesion and proliferation. MSCs on cross-linked multilayers grew to confluence. Using comparative confocal microscopy analysis of PLL/HA multilayers with physically adsorbed versus chemically coupled FN, we demonstrated that cross-linking strongly influenced FN surface distribution, leading to denser presentation of adhesion sites for cells. The covalent affixation of FN promoted focal adhesion formation and was critical to maintaining densely grown MSC cultures over weeks for their differentiation. Multilayer-bound MSCs were capable of differentiating into osteocytes and chondrocytes upon culture with induction factors. Together, cross-linked, FN-terminated PLL/HA multilayers provide a versatile platform for studies of human MSCs for biotechnological or therapeutic applications.
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