Critical Impact of Human Amniotic Membrane Tension on Mitochondrial Function and Cell Viability In Vitro.

Amniotic cells show exciting stem cell features, which has led to the idea of using living cells of human amniotic membranes (hAMs) in toto for clinical applications. However, under common cell culture conditions, viability of amniotic cells decreases rapidly, whereby reasons for this decrease are unknown so far. Recently, it has been suggested that loss of tissue tension in vivo leads to apoptosis. Therefore, the aim of this study was to investigate the effect of tissue distention on the viability of amniotic cells in vitro. Thereby, particular focus was put on vital mitochondria-linked parameters, such as respiration and ATP synthesis. Biopsies of hAMs were incubated for 7-21 days either non-distended or distended. We observed increased B-cell lymphoma 2-associated X protein (BAX)/B-cell lymphoma (BCL)-2 ratios in non-distended hAMs at day seven, followed by increased caspase 3 expression at day 14, and, consequently, loss of viability at day 21. In contrast, under distention, caspase 3 expression increased only slightly, and mitochondrial function and cellular viability were largely maintained. Our data suggest that a mechano-sensing pathway may control viability of hAM cells by triggering mitochondria-mediated apoptosis upon loss of tension in vitro. Further studies are required to elucidate the underlying molecular mechanisms between tissue distention and viability of hAM cells.

Oxygen Tension Strongly Influences Metabolic Parameters and the Release of Interleukin-6 of Human Amniotic Mesenchymal Stromal Cells In Vitro.

The human amniotic membrane (hAM) has been used for tissue regeneration for over a century. In vivo (in utero), cells of the hAM are exposed to low oxygen tension (1-4% oxygen), while the hAM is usually cultured in atmospheric, meaning high, oxygen tension (20% oxygen). We tested the influence of oxygen tensions on mitochondrial and inflammatory parameters of human amniotic mesenchymal stromal cells (hAMSCs). Freshly isolated hAMSCs were incubated for 4 days at 5% and 20% oxygen. We found 20% oxygen to strongly increase mitochondrial oxidative phosphorylation, especially in placental amniotic cells. Oxygen tension did not impact levels of reactive oxygen species (ROS); however, placental amniotic cells showed lower levels of ROS, independent of oxygen tension. In contrast, the release of nitric oxide was independent of the amniotic region but dependent on oxygen tension. Furthermore, IL-6 was significantly increased at 20% oxygen. To conclude, short-time cultivation at 20% oxygen of freshly isolated hAMSCs induced significant changes in mitochondrial function and release of IL-6. Depending on the therapeutic purpose, cultivation conditions of the cells should be chosen carefully for providing the best possible quality of cell therapy.

Cellular and Site-Specific Mitochondrial Characterization of Vital Human Amniotic Membrane.

Over a century ago, clinicians started to use the human amniotic membrane for coverage of wounds and burn injuries. To date, literally thousands of different clinical applications exist for this biomaterial almost exclusively in a decellularized or denuded form. Recent reconsiderations for the use of vital human amniotic membrane for clinical applications would take advantage of the versatile cells of embryonic origin including the entirety of their cell organelles. Recently, more and more evidence was found, showing mitochondria to be involved in most fundamental cellular processes, such as differentiation and cell death. In this study, we focused on specific properties of mitochondria of vital human amniotic membrane and characterized bioenergetical parameters of 2 subregions of the human amniotic membrane, the placental and reflected amnion. We found significantly different levels of adenosine triphosphate (ATP) and extracellular reactive oxygen species, concentrations of succinate dehydrogenase, and lactate upon inhibition of ATP synthase in placental and reflected amnion. We also found significantly different rates of mitochondrial respiration in isolated human amniotic epithelial cells and human amniotic mesenchymal stromal cells, according to the subregions. Differences in metabolic activities were inversely related to mitochondrial DNA copy numbers in isolated cells of placental and reflected amnion. Based on significant differences of several key parameters of energy metabolism in 2 subregions of vital amnion, we propose that these metabolic differences of vital placental and reflected amnion could have critical impact on therapeutic applications. Inclusion of region-specific metabolic properties could optimize and fine-tune the clinical application of the human amniotic membrane and improve the outcome significantly.

Effects of amniotic epithelial cell transplantation in endothelial injury.

PURPOSE: Human amniotic epithelial cells (hAECs) are promising tools for endothelial repair in vascular regenerative medicine. We hypothesized that these epithelial cells are capable of repairing the damaged endothelial layer following balloon injury of the carotid artery in adult male rats. RESULTS: Two days after injury, the transplanted hAECs were observed at the luminal side of the arterial wall. Then, 4 weeks after the injury, significant intimal thickening was observed in both untreated and cell implanted vessels. Constriction was decreased in both implanted and control animals. Immunohistochemical analysis showed a few surviving cells in the intact arterial wall, but no cells were observed at the site of injury. Interestingly, acetylcholine-induced dilation was preserved in the intact side and the sham-transplanted injured arteries, but it was a trend toward decreased vasodilation in the hAECs' transplanted vessels. CONCLUSION: We conclude that hAECs were able to incorporate into the arterial wall without immunosuppression, but failed to improve vascular function, highlighting that morphological implantation does not necessarily result in functional benefits and underscoring the need to understand other mechanisms of endothelial regeneration.

Different metabolic activity in placental and reflected regions of the human amniotic membrane.

Cells of the human amniotic membrane (hAM) have stem cell characteristics with low immunogenicity and anti-inflammatory properties. While hAM is an excellent source for tissue engineering, so far, its sub-regions have not been taken into account. We show that placental and reflected hAM differ distinctly in morphology and functional activity, as the placental region has significantly higher mitochondrial activity, however significantly less reactive oxygen species. Since mitochondria may participate in processes such as cell rescue, we speculate that amniotic sub-regions may have different potential for tissue regeneration, which may be crucial for clinical applications.

Intact human amniotic membrane differentiated towards the chondrogenic lineage.

Human amniotic membrane (hAM) represents a tissue that is well established as biomaterial in the clinics with potential for new applications in regenerative medicine. For tissue engineering (TE) strategies, cells are usually combined with inductive factors and a carrier substrate. We have previously recognized that hAM represents a natural, preformed sheet including highly potent stem cells. In the present approach for cartilage regeneration we have induced chondrogenesis in hAM in vitro. For this, hAM biopsies were cultured for up to 56 days under chondrogenic conditions. The induced hAM was characterized for remaining viability, glycosaminoglycan (GAG) accumulation using histochemical analysis, and a quantitative assay. Collagen I, II and X was immunohistochemically determined and cartilage-specific mRNA expression of (sex determining region Y-) box 9, cartilage oligomeric matrix protein (COMP), aggrecan (AGC1), versican (CSPG2), COL1A1, COL9A2, melanoma inhibitory activity (MIA), and cartilage-linking protein 1 (CRTL1) analyzed by quantitative real-time polymerase chain reaction. Human AM was successfully induced to accumulate GAG, as demonstrated by Alcianblue staining and a significant (p < 0.001) increase of GAG/viability under chondrogenic conditions peaking in a 29.9 ± 0.9-fold induction on day 56. Further, upon chondrogenic induction collagen II positive areas were identified within histological sections and cartilage-specific markers including COMP, AGC1, CSPG2, COL1A1, COL9A2, MIA, and CRTL1 were found upregulated at mRNA level. This is the first study, demonstrating that upon in vitro induction viable human amnion expresses cartilage-specific markers and accumulates GAGs within the biomatrix. This is a promising first step towards a potential use of living hAM for cartilage TE.

Anti-fibrotic effects of fresh and cryopreserved human amniotic membrane in a rat liver fibrosis model.

The human amniotic membrane (hAM), thanks to its favorable properties, including anti-inflammatory, anti-fibrotic and pro-regenerative effects, is a well-known surgical material for many clinical applications, when used both freshly after isolation and after preservation. We have shown previously that hAM patching is a potential approach to counteract liver fibrosis. Indeed, when fresh hAM was used to cover the liver surface of rats with liver fibrosis induced by the bile duct ligation (BDL) procedure, the progression and severity of fibrosis were significantly reduced. Since cryopreservation enables safety and long-term storage of hAM but may influence its functional properties, here we compared the anti-fibrotic effects of fresh and cryopreserved hAM in rats with BDL-induced liver fibrosis. After BDL, the rat liver was covered with a piece of fresh or cryopreserved hAM, or left untreated. Six weeks later, the degree of liver fibrosis was assessed histologically using the Knodell and the METAVIR scoring systems. Digital image analysis was used to quantify the percentage of the areas of each liver section displaying ductular reaction, extracellular matrix (ECM) deposition, activated myofibroblasts and hepatic stellate cells (HSCs). Liver collagen content was also determined by spectrophotometric technique. The degree of liver fibrosis, ductular reaction, ECM deposition, and the number of activated myofibroblasts and HSCs were all significantly reduced in hAM-treated rats compared to control animals. Fresh and cryopreserved hAM produced the same anti-fibrotic effects. These findings indicate that cryopreservation maintains the anti-fibrotic properties of hAM when used as a patch to reduce the severity of liver fibrosis.

Human-derived alternatives to fetal bovine serum in cell culture.

OBJECTIVE: The need for an alternative to fetal bovine serum (FBS) is known to scientists and users involved in cell therapy or advanced therapy medicinal products. Human serum (huS) and platelet lysate (hPL) can be used as alternatives resulting in similar or even superior results concerning cell expansion. METHODS: We developed protocols for the production of huS and two types of hPL and tested them in the expansion of human fibroblasts and adipose tissue-derived stem cells (ASC). Quality control included cell counts (platelets, red and white blood cells), sterility testing, pH levels, total protein concentrations and growth factor levels. ASC and fibroblasts were expanded for three passages in media supplemented with FBS, huS or hPL and evaluated microscopically. Proliferation in terms of population doubling times (PDT) was determined. In case of ASC, differentiation was performed as well. RESULTS: All three alternatives demonstrated shorter PDT for fibroblasts and ASC compared to FBS. Furthermore, ASC maintained their differentiation potential. CONCLUSION: We conclude that hPL and huS can be used as alternatives to FBS for the cultivation and expansion of cells intended for human use.

Mesenchymal stem or stromal cells from amnion and umbilical cord tissue and their potential for clinical applications.

Mesenchymal stem or stromal cells (MSC) have proven to offer great promise for cell-based therapies and tissue engineering applications, as these cells are capable of extensive self-renewal and display a multilineage differentiation potential. Furthermore, MSC were shown to exhibit immunomodulatory properties and display supportive functions through parakrine effects. Besides bone marrow (BM), still today the most common source of MSC, these cells were found to be present in a variety of postnatal and extraembryonic tissues and organs as well as in a large variety of fetal tissues. Over the last decade, the human umbilical cord and human amnion have been found to be a rich and valuable source of MSC that is bio-equivalent to BM-MSC. Since these tissues are discarded after birth, the cells are easily accessible without ethical concerns.

Osteogenic differentiation of intact human amniotic membrane.

Tissue engineering strategies usually require cell isolation and combination with a suitable biomaterial. Human amniotic membrane (AM) represents a natural two-layered sheet comprising cells with proven stem cell characteristics. In our approach, we evaluated the differentiation potential of AM in toto with its sessile stem cells as alternative to conventional approaches requiring cell isolation and combination with biomaterials. For this, AM-biopsies were differentiated in vitro using two osteogenic media compared with control medium (CM) for 28 days. Mineralization and osteocalcin expression was demonstrated by (immuno)histochemistry. Alkaline phosphatase (AP) activity, calcium contents and mRNA expression of RUNX2, AP, osteopontin, osteocalcin, BMP-2 (bone morphogenetic protein), and BMP-4 were quantified and AM viability was evaluated. Under osteogenic conditions, AM-biopsies mineralized successfully and by day 28 the majority of cells expressed osteocalcin. This was confirmed by a significant rise in calcium contents (up to 27.4 ± 6.8 mg/dl d28), increased AP activity, and induction of RUNX2, AP, BMP-2 and BMP-4 mRNA expression. Relatively high levels of viability were retained, especially in osteogenic media (up to 78.3 ± 19.0% d14; 62.9 ± 22.3% d28) compared to CM (42.2 ± 15.2% d14; 35.1 ± 8.6% d28). By this strategy, stem cells within human AM can successfully be driven along the osteogenic pathways while residing within their natural environment.

Fatty acids induce apoptosis in human smooth muscle cells depending on chain length, saturation, and duration of exposure.

OBJECTIVE: Plasma free fatty acid (FFA) concentrations are increased in states of insulin resistance. Therefore, this study evaluated apoptosis and underlying mechanisms induced by selected nutritional FFAs, a defined FFA-mix, and human plasma containing high FFA concentrations in human smooth muscle cells (HSMCs). RESEARCH DESIGN AND METHODS: HSMCs were incubated (24-72 h) with selected FFAs (100-300 micromol/l), an FFA-mix (palmitic-/stearic-/oleic-/linoleic-/alpha-linolenic acid=2.6/1/3.6/9/1; 300-900 micromol/l), or with high FFA-plasma (600 micromol/l) versus respective control cultures. Apoptosis, caspase activation, and protein expression were determined by DNA-fragmentation assays, flow cytometry, and Western blots, respectively. RESULTS: Exposure (24h) of HSMCs to 300 micromol/l stearic-, oleic-, linoleic-, alpha-linolenic-, and arachidonic acid induced apoptosis, correlating (p<0.01) with the FFAs' chain length (r=0.602) and number of FFA double bonds (r=0.956). After 48 h, 100 micromol/l of all tested FFAs - including palmitic acid - were already sufficient to trigger HSMCs' cell death. FFA-exposure resulted in activation of caspases and apoptosis was completely abolished by co-incubation with caspase inhibitors and negatively correlated (p<0.01) with the base-excision repair protein XRCC1 (r=-0.765) and with c-myc's antagonist mad (r=-0.916), whereas positive correlations (p<0.01) were found for protein expression of the proto-oncogene c-myc (r=0.972) and the transcription factor E2F-1 (r=0.971). Exposure of HSMCs to the defined FFA-mix and to plasma samples from individuals with elevated plasma FFAs supported the results obtained by defined FFA stimulation. CONCLUSIONS: Since smooth muscle cells surround the macrophage/foam cell/lipid-laden artheromatous core of atherosclerotic lesions with a protective fibrous cap, their FFA-induced HSMC apoptosis could contribute to progression of atherosclerosis by thinning of the fibrous cap and subsequent plaque destabilization.

Different mechanisms of saturated versus polyunsaturated FFA-induced apoptosis in human endothelial cells.

Apoptosis and underlying mechanisms were evaluated in human umbilical vein endothelial cells (HUVECs), in target tissues of late diabetic vascular complications [human aortic endothelial cells (HAECs) and human retinal endothelial cells (HRECs)], and in endothelial progenitor cells (EPCs) exposed to FFAs, which are elevated in obesity and diabetes. Saturated stearic acid concentration dependently induced apoptosis that could be mediated via reduced membrane fluidity, because both apoptosis and membrane rigidity are counteracted by eicosapentaenoic acid. PUFAs triggered apoptosis at a concentration of 300 micromol/l in HUVECs, HAECs, and EPCs, but not HRECs, and, in contrast to stearic acid, involved caspase-8 activation. PUFA-induced apoptosis, but not stearic acid-induced apoptosis, strictly correlated (P < 0.01) with protein expression of E2F-1 (r = 0.878) and c-myc (r = 0.966). Lack of c-myc expression and activity owing to quiescence or transfection with dominant negative In373-Myc, respectively, renders HUVECs resistant to PUFA-induced apoptosis. Because c-myc is abundant in growing cells only, apoptosis triggered by PUFAs, but not by saturated stearic acid, obviously depends on the growth/proliferation status of the cells. Finally, this study shows that FFA-induced apoptosis depends on the vascular origin and growth/proliferation status of endothelial cells, and that saturated stearic acid-induced apoptosis and PUFA-induced apoptosis are mediated via different mechanisms.