Daniel Hägg

3D Bioprinting Human Chondrocytes with Nanocellulose–Alginate Bioink for Cartilage Tissue Engineering Applications

The introduction of 3D bioprinting is expected to revolutionize the field of tissue engineering and regenerative medicine. The 3D bioprinter is able to dispense materials while moving in X, Y, and Z directions, which enables the engineering of complex structures from the bottom up. In this study, a bioink that combines the outstanding shear thinning properties of nanofibrillated cellulose (NFC) with the fast cross-linking ability of alginate was formulated for the 3D bioprinting of living soft tissue with cells. Printability was evaluated with concern to printer parameters and shape fidelity. The shear thinning behavior of the tested bioinks enabled printing of both 2D gridlike structures as well as 3D constructs. Furthermore, anatomically shaped cartilage structures, such as a human ear and sheep meniscus, were 3D printed using MRI and CT images as blueprints. Human chondrocytes bioprinted in the noncytotoxic, nanocellulose-based bioink exhibited a cell viability of 73% and 86% after 1 and 7 days of 3D culture, respectively. On the basis of these results, we can conclude that the nanocellulose-based bioink is a suitable hydrogel for 3D bioprinting with living cells. This study demonstrates the potential use of nanocellulose for 3D bioprinting of living tissues and organs.

The VLDL receptor promotes lipotoxicity and increases mortality in mice following an acute myocardial infarction

Impaired cardiac function is associated with myocardial triglyceride accumulation, but it is not clear how the lipids accumulate or whether this accumulation is detrimental. Here we show that hypoxia/ischemia-induced accumulation of lipids in HL-1 cardiomyocytes and mouse hearts is dependent on expression of the VLDL receptor (VLDLR). Hypoxia-induced VLDLR expression in HL-1 cells was dependent on HIF-1α through its interaction with a hypoxia-responsive element in the Vldlr promoter, and VLDLR promoted the endocytosis of lipoproteins. Furthermore, VLDLR expression was higher in ischemic compared with nonischemic left ventricles from human hearts and was correlated with the total lipid droplet area in the cardiomyocytes. Importantly, Vldlr-/- mice showed improved survival and decreased infarct area following an induced myocardial infarction. ER stress, which leads to apoptosis, is known to be involved in ischemic heart disease. We found that ischemia-induced ER stress and apoptosis in mouse hearts were reduced in Vldlr-/- mice and in mice treated with antibodies specific for VLDLR. These findings suggest that VLDLR-induced lipid accumulation in the ischemic heart worsens survival by increasing ER stress and apoptosis.

Cartilage Tissue Engineering by the 3D Bioprinting of iPS Cells in a Nanocellulose/Alginate Bioink

Cartilage lesions can progress into secondary osteoarthritis and cause severe clinical problems in numerous patients. As a prospective treatment of such lesions, human-derived induced pluripotent stem cells (iPSCs) were shown to be 3D bioprinted into cartilage mimics using a nanofibrillated cellulose (NFC) composite bioink when co-printed with irradiated human chondrocytes. Two bioinks were investigated: NFC with alginate (NFC/A) or hyaluronic acid (NFC/HA). Low proliferation and phenotypic changes away from pluripotency were seen in the case of NFC/HA. However, in the case of the 3D-bioprinted NFC/A (60/40, dry weight % ratio) constructs, pluripotency was initially maintained, and after five weeks, hyaline-like cartilaginous tissue with collagen type II expression and lacking tumorigenic Oct4 expression was observed in 3D -bioprinted NFC/A (60/40, dry weight % relation) constructs. Moreover, a marked increase in cell number within the cartilaginous tissue was detected by 2-photon fluorescence microscopy, indicating the importance of high cell densities in the pursuit of achieving good survival after printing. We conclude that NFC/A bioink is suitable for bioprinting iPSCs to support cartilage production in co-cultures with irradiated chondrocytes.

Expression of chemokine (C–C motif) ligand 18 in human macrophages and atherosclerotic plaques

OBJECTIVE Using gene expression profiling, we aimed to identify genes that are predominantly expressed in human carotid atherosclerotic plaques. Such genes may be important in atherogenesis and pathophysiology of the plaque, and genes that encode for secreted proteins may be potential biomarkers for atherosclerosis and cardiovascular disease. METHODS DNA microarray generated expression profiles of human carotid atherosclerotic plaques were compared to expression profiles of 80 different human tissues and cell types, to identify plaque-specific genes. RESULTS We identified the chemokine (C-C motif) ligand 18 (CCL18) as predominantly expressed in human carotid plaque. Immunohistochemistry showed that CCL18 protein was localized to a subset of macrophages in carotid plaques. Monocyte-derived macrophages from subjects with atherosclerosis had threefold higher expression of CCL18 than macrophages from control subjects (p=0.012). Subjects with A/G genotype of the rs2015086 SNP in the promoter region of the CCL18 gene had threefold higher macrophage expression of CCL18 than subjects with A/A genotype (p=0.049), but we found no association of this SNP with an increased risk of coronary heart disease. We also compared serum levels of CCL18 from subjects with symptomatic carotid artery disease with control subjects. There were no differences in serum levels of CCL18 between the two groups, however CCL18 correlated with measurements of adiposity. CONCLUSION CCL18 is predominantly expressed in human atherosclerotic plaques and may participate in the atherosclerotic plaque formation.

Evaluation of CXCL9 and CXCL10 as circulating biomarkers of human cardiac allograft rejection

BackgroundCardiac allograft rejection remains a significant clinical problem in the early phase after heart transplantation and requires frequent surveillance with endomyocardial biopsy. However, this is an invasive procedure, which is unpleasant for the patient and carries a certain risk. Therefore, a sensitive non-invasive biomarker of acute rejection would be desirable.MethodsEndomyocardial tissue samples and serum were obtained in connection with clinical biopsies from twenty consecutive heart transplant patients followed for six months. A rejection episode was observed in 14 patients (11 men and 3 women) and biopsies obtained before, during and after the episode were identified. Endomyocardial RNA, from three patients, matching these three points in time were analysed with DNA microarray. Genes showing up-regulation during rejection followed by normalization after the rejection episode were evaluated further with real-time RT-PCR. Finally, ELISA was performed to investigate whether change in gene-regulation during graft rejection was reflected in altered concentrations of the encoded protein in serum.ResultsThree potential cardiac allograft rejection biomarker genes, chemokine (C-X-C motif) ligand 9 (CXCL9), chemokine (C-X-C motif) ligand 10 (CXCL10) and Natriuretic peptide precursor A (NPPA), from the DNA microarray analysis were selected for further evaluation. CXCL9 was significantly upregulated during rejection (p < 0.05) and CXCL10 displayed a similar pattern without reaching statistical significance. Serum levels of CXCL9 and CXCL10 were measured by ELISA in samples from 10 patients before, during and after cardiac rejection. There were no changes in CXCL9 and CXCL10 serum concentrations during cardiac rejection. Both chemokines displayed large individual variations in the selected samples, but the serum levels between the two chemokines correlated (p < 0.001).ConclusionWe conclude, that despite a distinct up-regulation of CXCL9 mRNA in human hearts during cardiac allograft rejection, this was not reflected in the serum levels of the encoded protein. Thus, in contrast to previous suggestions, serum CXCL9 does not appear to be a promising serum biomarker for cardiac allograft rejection.

Adipogenic differentiation of stem cells in three-dimensional porous bacterial nanocellulose scaffolds.

There is an increased interest in developing adipose tissue for in vitro and in vivo applications. Current two-dimensional (2D) cell-culture systems of adipocytes are limited, and new methods to culture adipocytes in three-dimensional (3D) are warranted as a more life-like model to study metabolic diseases such as obesity and diabetes. In this study, we have evaluated different porous bacterial nanocellulose scaffolds for 3D adipose tissue. In an initial pilot study, we compared adipogenic differentiation of mice mesenchymal stem cells from a cell line on 2D and 3D scaffolds of bacterial nanocellulose. The 3D scaffolds were engineered by crosslinking homogenized cellulose fibrils using alginate and freeze drying the mixture to obtain a porous structure. Quenching the scaffolds in liquid nitrogen resulted in smaller pores compared to slower freezing using isopropanol. We found that on 2D surfaces, the cells were scarcely distributed and showed limited formation of lipid droplets, whereas cells grown in macroporous 3D scaffolds contained more cells growing in clusters, containing large lipid droplets. All four types of scaffolds contained a lot of adipocytes, but scaffolds with smaller pores contained larger cell clusters than scaffolds with bigger pores, with viable adipocytes present even 4 weeks after differentiation. Scaffolds with lower alginate fractions retained their pore integrity better. We conclude that 3D culturing of adipocytes in bacterial nanocellulose macroporous scaffolds is a promising method for fabrication of adipose tissue as an in vitro model for adipose biology and metabolic disease.

In situ forming spruce xylan-based hydrogel for cell immobilization.

An in situ forming spruce xylan-based hydrogel was synthesized in two steps with the intended use of cell encapsulation and in vivo delivery. First, bioconjugate was obtained through the reaction of glucuronic acid groups from xylan backbone with tyramine (TA). After that, the gelation process was enabled by enzymatic crosslinking of the phenol-containing TA-xylan conjugate. Exhibiting an exponential increase in the storage modulus, a 3D gel network was formed in about 20s. The designed gel showed extensive swelling and retained its mechanical integrity for more than two months. Mesenchymal stem cells were encapsulated in the hydrogel and cultured for one week. The cells retained their adipogenic differentiation capacity inside the gel, as verified by lipid accumulation. From these facts, we conclude that spruce xylan is a promising precursor for in situ forming hydrogels and should be evaluated further for tissue engineering purposes.

Regulation and splicing of scavenger receptor class B type I in human macrophages and atherosclerotic plaques

BackgroundThe protective role of high-density lipoprotein (HDL) in the cardiovascular system is related to its role in the reverse transport of cholesterol from the arterial wall to the liver for subsequent excretion via the bile. Scavenger receptor class B type I (SR-BI) binds HDL and mediates selective uptake of cholesterol ester and cellular efflux of cholesterol to HDL. The role of SR-BI in atherosclerosis has been well established in murine models but it remains unclear whether SR-BI plays an equally important role in atherosclerosis in humans. The aim of this study was to investigate the expression of SR-BI and its isoforms in human macrophages and atherosclerotic plaques.MethodsThe effect of hypoxia and minimally modified low-density lipoprotein (mmLDL), two proatherogenic stimuli, on SR-BI expression was studied in human monocyte-derived macrophages from healthy subjects using real-time PCR. In addition, SR-BI expression was determined in macrophages obtained from subjects with atherosclerosis (n = 15) and healthy controls (n = 15). Expression of SR-BI isoforms was characterized in human atherosclerotic plaques and macrophages using RT-PCR and DNA sequencing.ResultsSR-BI expression was decreased in macrophages after hypoxia (p < 0.005). In contrast, SR-BI expression was increased by exposure to mmLDL (p < 0.05). There was no difference in SR-BI expression in macrophages from patients with atherosclerosis compared to controls. In both groups, SR-BI expression was increased by exposure to mmLDL (p < 0.05). Transcripts corresponding to SR-BI and SR-BII were detected in macrophages. In addition, a third isoform, referred to as SR-BIII, was discovered. All three isoforms were also expressed in human atherosclerotic plaque. Compared to the other isoforms, the novel SR-BIII isoform was predicted to have a unique intracellular C-terminal domain containing 53 amino acids.ConclusionWe conclude that SR-BI is regulated by proatherogenic stimuli in humans. However, we found no differences between subjects with atherosclerosis and healthy controls. This indicates that altered SR-BI expression is not a common cause of atherosclerosis. In addition, we identified SR-BIII as a novel isoform expressed in human macrophages and in human atherosclerotic plaques.

Universal method for protein bioconjugation with nanocellulose scaffolds for increased cell adhesion

Bacterial nanocellulose (BNC) is an emerging biomaterial since it is biocompatible, integrates well with host tissue and can be biosynthesized in desired architecture. However, being a hydrogel, it exhibits low affinity for cell attachment, which is crucial for the cellular fate process. To increase cell attachment, the surface of BNC scaffolds was modified with two proteins, fibronectin and collagen type I, using an effective bioconjugation method applying 1-cyano-4-dimethylaminopyridinium (CDAP) tetrafluoroborate as the intermediate catalytic agent. The effect of CDAP treatment on cell adhesion to the BNC surface is shown for human umbilical vein endothelial cells and the mouse mesenchymal stem cell line C3H10T1/2. In both cases, the surface modification increased the number of cells attached to the surfaces. In addition, the morphology of the cells indicated more healthy and viable cells. CDAP activation of bacterial nanocellulose is shown to be a convenient method to conjugate extracellular proteins to the scaffold surfaces. CDAP treatment can be performed in a short period of time in an aqueous environment under heterogeneous and mild conditions preserving the nanofibrillar network of cellulose.

Enhanced growth of neural networks on conductive cellulose-derived nanofibrous scaffolds

The problem of recovery from neurodegeneration needs new effective solutions. Tissue engineering is viewed as a prospective approach for solving this problem since it can help to develop healthy neural tissue using supportive scaffolds. This study presents effective and sustainable tissue engineering methods for creating biomaterials from cellulose that can be used either as scaffolds for the growth of neural tissue in vitro or as drug screening models. To reach this goal, nanofibrous electrospun cellulose mats were made conductive via two different procedures: carbonization and addition of multi-walled carbon nanotubes. The resulting scaffolds were much more conductive than untreated cellulose material and were used to support growth and differentiation of SH-SY5Y neuroblastoma cells. The cells were evaluated by scanning electron microscopy and confocal microscopy methods over a period of 15 days at different time points. The results showed that the cellulose-derived conductive scaffolds can provide support for good cell attachment, growth and differentiation. The formation of a neural network occurred within 10 days of differentiation, which is a promising length of time for SH-SY5Y neuroblastoma cells.