17β-Hydroxysteroid dehydrogenase type 7 (Hsd17b7) reverts cholesterol auxotrophy in NS0 cells

Identification of Candidate Genes and Regulatory Competitive Endogenous RNA (ceRNA) Networks Underlying Intramuscular Fat Content in Yorkshire Pigs with Extreme Fat Deposition Phenotypes

Intramuscular fat (IMF) content is vital for pork quality, serving an important role in economic performance in pig industry. Non-coding RNAs, with mRNAs, are involved in IMF deposition; however, their functions and regulatory mechanisms in porcine IMF remain elusive. This study assessed the whole transcriptome expression profiles of the Longissimus dorsi muscle of pigs with high (H) and low (L) IMF content to identify genes implicated in porcine IMF adipogenesis and their regulatory functions. Hundreds of differentially expressed RNAs were found to be involved in fatty acid metabolic processes, lipid metabolism, and fat cell differentiation. Furthermore, combing co-differential expression analyses, we constructed competing endogenous RNAs (ceRNA) regulatory networks, showing crosstalk among 30 lncRNAs and 61 mRNAs through 20 miRNAs, five circRNAs and 11 mRNAs through four miRNAs, and potential IMF deposition-related ceRNA subnetworks. Functional lncRNAs and circRNAs (such as MSTRG.12440.1, ENSSSCT00000066779, novel_circ_011355, novel_circ_011355) were found to act as ceRNAs of important lipid metabolism-related mRNAs (LEP, IP6K1, FFAR4, CEBPA, etc.) by sponging functional miRNAs (such as ssc-miR-196a, ssc-miR-200b, ssc-miR10391, miR486-y). These findings provide potential regulators and molecular regulatory networks that can be utilized for research on IMF traits in pigs, which would aid in marker-assisted selection to improve pork quality.

Transcriptional Insights into Key Genes and Pathways Underlying Muscovy Duck Subcutaneous Fat Deposition at Different Developmental Stages

Simple Summary

Subcutaneous fat is an important factor affecting the meat quality and feed conversion rate of waterfowl. The current study compared the transcriptome data of Muscovy duck subcutaneous fat among three developmental stages, aiming at exploring the key regulatory genes for subcutaneous fat deposition. The results generated abundant candidate genes and pathways involving in subcutaneous fat deposition in Muscovy duck. This study provides an important reference for revealing the developmental mechanisms of subcutaneous fat in duck.

Abstract

Subcutaneous fat is a crucial trait for waterfowl, largely associated with meat quality and feed conversion rate. In this study, RNA-seq was used to identify differentially expressed genes of subcutaneous adipose tissue among three developmental stages (12, 35, and 66 weeks) in Muscovy duck. A total of 138 and 129 differentially expressed genes (DEGs) were identified between 35 and 12 weeks (wk), and 66 and 35 wk, respectively. Compared with 12 wk, subcutaneous fat tissue at 35 wk upregulated several genes related to cholesterol biosynthesis and fatty acid biosynthesis, including HSD17B7 and MSMO1, while it downregulated fatty acid beta-oxidation related genes, including ACOX1 and ACSL1. Notably, most of the DEGs (92.2%) were downregulated in 66 wk compared with 35 wk, consistent with the slower metabolism of aging duck. Protein network interaction and function analyses revealed GC, AHSG, FGG, and FGA were the key genes for duck subcutaneous fat from adult to old age. Additionally, the PPAR signaling pathway, commonly enriched between the two comparisons, might be the key pathway contributing to subcutaneous fat metabolism among differential developmental stages in Muscovy duck. These results provide several candidate genes and pathways potentially involved in duck subcutaneous fat deposition, expanding our understanding of the molecular mechanisms underlying subcutaneous fat deposition during development.

Transcriptome analysis to assess the cholestatic hepatotoxicity induced by Polygoni Multiflori Radix: Up-regulation of key enzymes of cholesterol and bile acid biosynthesis

Polygoni Multiflori Radix (PMR) has been commonly used as a tonic in China for centuries. However, PMR-associated hepatotoxicity is becoming a safety issue. Cholestasis often occurs in PMR-induced hepatotoxicity in clinical medicine, but the exact mechanism is not completely understood. An RNA-Seq method was employed, in the present study, to explore the molecular mechanism of cholestatic liver injury induced by PMR, characterized by the hepatic transcriptional response in rats exposed to 1 and 20 g/kg PMR for 90 days. Pathological changes seen in rat livers exposed to PMR included increased bile ducts in portal areas and biliary epithelial cell hyperplasia, which were accompanied by the elevation of serum biochemistries. Dose-dependent increases in the expression of 14 transcripts encoding enzymes involved in the cholesterol biosynthetic pathway were identified. Furthermore, cholesterol 7-alpha hydroxylase (Cyp7a1), a rate-limiting enzyme in the synthesis of bile acids (BAs) from cholesterol, was found to be upregulated by PMR treatment. Protein analysis by western blot suggested that expression of 3-hydroxy-3-methylglutaryl CoA reductase (Hmgcr) and Cyp7a1 were increased in a dose-dependent manner. Collectively, the present study demonstrates that PMR upregulates key enzymes for biosynthesis of cholesterol and BA, which poses the risk of cholestatic liver injury.

SIGNIFICANCE

To the best of our knowledge, this is the first transcriptome analysis to highlight the main molecular changes occurring in rats chronic exposed to PMR. We have identified 39 specific differentially expressed genes (DEGs) that were present in various comparisons. A total of 14 of these altered gene transcripts were associated with cholesterol biosynthesis. Another factor of great importance in our opinion seemed to be the enhancement of bile acid (BA) biosynthesis, which were closely linked to cholesterol biosynthesis or metabolism. Our findings suggested that the disturbance on balance of BA formation and elimination might lead to a BA overload in hepatocytes, thereby resulting in liver injury.

miR-92a enhances recombinant protein productivity in CHO cells by increasing intracellular cholesterol levels

MicroRNAs (miRNAs) have emerged as promising targets for engineering of CHO cell factories to enhance recombinant protein productivity. Manipulation of miRNA levels in CHO cells have been shown to improve product yield by increasing proliferation and specific productivity (qP), resisting apoptosis and enhancing oxidative metabolism. The authors previously demonstrated that over-expressing miR-92a results in increases in qP and titer of CHO-IgG cells. However, the mechanisms by which miR-92a enhances qP in CHO cells are still uninvestigated. Here, the authors report the identification of insig1, a regulator of cholesterol biosynthesis, as a target of miR-92a using computational prediction. Both transient and stable over-expression of miR-92a decreased the expression levels of insig1. Insig1 was further validated as a target of miR-92a using 3' UTR reporter assay. Intracellular cholesterol concentration of two high-producing miR-92a clones were significantly increased by ≈30% compared to the blank-transfected pool. Relative Golgi surface area was also found to be 18-26% higher in these clones. Our findings suggest that miR-92a may affect cholesterol metabolism by repressing insig1, resulting in raised intracellular cholesterol levels and Golgi volume and hence enhanced protein secretion.

Unveiling gene trait relationship by cross-platform meta-analysis on Chinese hamster ovary cell transcriptome

In the past few years, transcriptome analysis has been increasingly employed to better understand the physiology of Chinese hamster ovary (CHO) cells at a global level. As more transcriptome data accumulated, meta-analysis on data sets collected from various sources can potentially provide better insights on common properties of those cells. Here, we performed meta-analysis on transcriptome data of different CHO cell lines obtained using NimbleGen or Affymetrix microarray platforms. Hierarchical clustering, non-negative matrix factorization (NMF) analysis, and principal component analysis (PCA) accordantly showed the samples were clustered into two groups: one consists of adherent cells in serum-containing medium, and the other suspension cells in serum-free medium. Genes that were differentially expressed between the two clusters were enriched in a few functional classes by Database for Annotation, Visualization, and Integrated Discovery (DAVID) of which many were common with the enriched gene sets identified by Gene Set Enrichment Analysis (GSEA), including extracellular matrix (ECM) receptor interaction, cell adhesion molecules (CAMs), and lipid related metabolism pathways. Despite the heterogeneous sources of the cell samples, the adherent and suspension growth characteristics and serum-supplementation appear to be a dominant feature in the transcriptome. The results demonstrated that meta-analysis of transcriptome could uncover features in combined data sets that individual data set might not reveal. As transcriptome data sets accumulate over time, meta-analysis will become even more revealing. Biotechnol. Bioeng. 2017;114: 1583-1592. © 2017 Wiley Periodicals, Inc.

Alterations of a Cellular Cholesterol Metabolism Network Are a Molecular Feature of Obesity-Related Type 2 Diabetes and Cardiovascular Disease

Obesity is linked to type 2 diabetes (T2D) and cardiovascular diseases; however, the underlying molecular mechanisms remain unclear. We aimed to identify obesity-associated molecular features that may contribute to obesity-related diseases. Using circulating monocytes from 1,264 Multi-Ethnic Study of Atherosclerosis (MESA) participants, we quantified the transcriptome and epigenome. We discovered that alterations in a network of coexpressed cholesterol metabolism genes are a signature feature of obesity and inflammatory stress. This network included 11 BMI-associated genes related to sterol uptake (↑LDLR, ↓MYLIP), synthesis (↑SCD, FADS1, HMGCS1, FDFT1, SQLE, CYP51A1, SC4MOL), and efflux (↓ABCA1, ABCG1), producing a molecular profile expected to increase intracellular cholesterol. Importantly, these alterations were associated with T2D and coronary artery calcium (CAC), independent from cardiometabolic factors, including serum lipid profiles. This network mediated the associations between obesity and T2D/CAC. Several genes in the network harbored C-phosphorus-G dinucleotides (e.g., ABCG1/cg06500161), which overlapped Encyclopedia of DNA Elements (ENCODE)-annotated regulatory regions and had methylation profiles that mediated the associations between BMI/inflammation and expression of their cognate genes. Taken together with several lines of previous experimental evidence, these data suggest that alterations of the cholesterol metabolism gene network represent a molecular link between obesity/inflammation and T2D/CAC.

Cell line development for biomanufacturing processes: recent advances and an outlook

At the core of a biomanufacturing process for recombinant proteins is the production cell line. It influences the productivity and product quality. Its characteristics also dictate process development, as the process is optimized to complement the producing cell to achieve the target productivity and quality. Advances in the past decade, from vector design to cell line screening, have greatly expanded our capability to attain producing cell lines with certain desired traits. Increasing availability of genomic and transcriptomic resources for industrially important cell lines coupled with advances in genome editing technology have opened new avenues for cell line development. These developments are poised to help biosimilar manufacturing, which requires targeting pre-defined product quality attributes, e.g., glycoform, to match the innovator's range. This review summarizes recent advances and discusses future possibilities in this area.

Updated survey of the steroid-converting enzymes in human adipose tissues

Over the past decade, adipose tissues have been increasingly known for their endocrine properties, that is, their ability to secrete a number of adipocytokines that may exert local and/or systemic effects. In addition, adipose tissues have long been recognized as significant sites for steroid hormone transformation and action. We hereby provide an updated survey of the many steroid-converting enzymes that may be detected in human adipose tissues, their activities and potential roles. In addition to the now well-established role of aromatase and 11β-hydroxysteroid dehydrogenase (HSD) type 1, many enzymes have been reported in adipocyte cell lines, isolated mature cells and/or preadipocytes. These include 11β-HSD type 2, 17β-HSDs, 3β-HSD, 5α-reductases, sulfatases and glucuronosyltransferases. Some of these enzymes are postulated to bear relevance for adipose tissue physiology and perhaps for the pathophysiology of obesity. This elaborate set of steroid-converting enzymes in the cell types of adipose tissue deserves further scientific attention. Our work on 20α-HSD (AKR1C1), 3α-HSD type 3 (AKR1C2) and 17β-HSD type 5 (AKR1C3) allowed us to clarify the relevance of these enzymes for some aspects of adipose tissue function. For example, down-regulation of AKR1C2 expression in preadipocytes seems to potentiate the inhibitory action of dihydrotestosterone on adipogenesis in this model. Many additional studies are warranted to assess the impact of intra-adipose steroid hormone conversions on adipose tissue functions and chronic conditions such as obesity, diabetes and cancer.

Characterization of a mutation that results in independence of oxidosqualene cyclase (Erg7) activity from the downstream 3-ketoreductase (Erg27) in the yeast ergosterol biosynthetic pathway

In yeast, deletion of ERG27, which encodes the sterol biosynthetic enzyme, 3-keto-reductase, results in a concomitant loss of the upstream enzyme, Erg7p, an oxidosqualene cyclase (OSC). However, this phenomenon occurs only in fungi, as mammalian Erg27p orthologues are unable to rescue yeast Erg7p activity. In this study, an erg27 mutant containing the mouse ERG27 orthologue was isolated that was capable of growing without sterol supplementation (FGerg27). GC/MS analysis of this strain showed an accumulation of squalene epoxides, 3-ketosterones, and ergosterol. This strain which was crossed to a wildtype and daughter segregants showed an accumulation of squalene epoxides as well as ergosterol indicating that the mutation entailed a leaky block at ERG7. Upon sequencing the yeast ERG7 gene an A598S alteration was found in a conserved alpha helical region. We theorize that this mutation stabilizes Erg7p in a conformation that mimics Erg27p binding. This mutation, while decreasing OSC activity still retains sufficient residual OSC activity such that the strain in the presence of the mammalian 3-keto reductase enzyme functions and no longer requires the yeast Erg27p. Because sterol biosynthesis occurs in the ER, a fusion protein was synthesized combining Erg7p and Erg28p, a resident ER protein and scaffold of the C-4 demethyation complex. Both FGerg27 and erg27 strains containing this fusion plasmid and the mouse ERG27 orthologue showed restoration of ergosterol biosynthesis with minimal accumulation of squalene epoxides. These results indicate retention of Erg7p in the ER increases its activity and suggest a novel method of regulation of ergosterol biosynthesis.

Gene expression profile in the liver tissue of geese after overfeeding

Geese form a fatty liver after feeding on a carbohydrate-rich diet, possibly as an evolutionary adaptation to accumulate reserves for migration. To gain insight into the gene-regulation processes of hepatic steatosis in geese, we examined the profile of transcriptional expression in goose fatty liver and control liver by suppression subtractive hybridization and measured the levels of serum biochemical variables. We found 107 genes whose expression was different between the treatment and control groups. The main functions of these genes are metabolic processes, including the metabolism of carbohydrates, amino acids, and lipids. Twenty-four genes were classified using the Kyoto Encyclopaedia of Genes and Genomes pathways. Twelve genes that related to metabolic and cellular processes were confirmed by quantitative RT-PCR. A specific positive effect of feeding was observed on the expression of genes involved mainly in unsaturated fatty acids and triglyceride synthesis, and a negative effect was observed on genes involved in β-oxidation, cholesterol metabolism, and glycolysis. The results could serve as an important reference for the development of goose breeding for fatty liver production and human liver disease research.

Divergent interactions involving the oxidosqualene cyclase and the steroid-3-ketoreductase in the sterol biosynthetic pathway of mammals and yeasts

In mammals and yeasts, oxidosqualene cyclase (OSC) catalyzes the formation of lanosterol, the first cyclic intermediate in sterol biosynthesis. We used a murine myeloma cell line (NS0), deficient in the 17β-hydroxysteroid dehydrogenase type 7 (HSD17B7), as a model to study the potential interaction of the HSD17B7 with the OSC in mammals. HSD17B7 is the orthologue of the yeast steroid-3-ketoreductase (ERG27), an enzyme of ergosterol biosynthesis that plays a protective role towards OSC. Tracer experiments with NS0 cells showed that OSC is fully active in these mammalian cells, suggesting that in mammals the ketosteroid reductase is not required for OSC activity. Mouse and human HSD17B7 were overexpressed in ERG27-deletant yeast cells, and recombinant strains were tested for (i) the ability to grow on different media, (ii) steroid-3-ketoreductase activity, and (iii) OSC activity. Recombinant strains grew more slowly than the control yeast ERG27-overexpressing strain on sterol-deficient media, whereas the growth rate was normal on media supplemented with a 3-ketoreductase substrate. The full enzymatic functionality of mammalian steroid-3-ketoreductase expressed in yeast along with the lack of (yeast) OSC activity point to an inability of the mammalian reductase to assist yeast OSC. Results demonstrate that in mammals, unlike in yeast, OSC and steroid-3-ketoreductase are non-interacting proteins.

Analysis of 17beta-hydroxysteroid dehydrogenase types 5, 7, and 12 genetic sequence variants in breast cancer cases from French Canadian Families with high risk of breast and ovarian cancer

A family history and estrogen exposure are well-known risk factors for breast cancer. Members of the 17beta-hydroxysteroid dehydrogenase family are responsible for important steps in the metabolism of androgens and estrogens in peripheral tissues, including the mammary gland. The crucial biological function of 17beta-HSDs renders these genes good candidates for being involved in breast cancer etiology. This study screened for mutations in HSD17B7 and HSD17B12 genes, which encode enzymes involved in estradiol biosynthesis and in AKR1C3, which codes for 17beta-HSD type 5 enzyme involved in androgen and progesterone metabolism, to assess whether high penetrance allelic variants in these genes could be involved in breast cancer susceptibility. Mutation screening of 50 breast cancer cases from non-BRCA1/2 high-risk French Canadian families failed to identify germline likely high-risk mutations in HSD17B7, HSD17B12 and AKR1C3 genes. However, 107 sequence variants were identified, including seven missense variants. Assessment of the impact of missense variants on enzymatic activity of the corresponding enzymes revealed no difference in catalytic properties between variants of 17beta-HSD types 7 and 12 and wild-type enzymes, while variants p.Glu77Gly and p.Lys183Arg in 17beta-HSD type 5 showed a slightly decreased activity. Finally, a haplotype-based approach was used to determine tagging SNPs providing valuable information for studies investigating associations of common variants in these genes with breast cancer risk.

Proliferation of NS0 cells in protein-free medium: the role of cell-derived proteins, known growth factors and cellular receptors

NS0 cells proliferate without external supply of growth factors in protein-free media. We hypothesize that the cells produce their own factors to support proliferation. Understanding the mechanisms behind this autocrine regulation of proliferation may open for the novel approaches to improve animal cell processes. The following proteins were identified in NS0 conditioned medium (CM): cyclophilin A, cyclophilin B (CypB), cystatin C, D-dopachrome tautomerase, IL-25, isopentenyl-diphosphate delta-isomerase, macrophage migration inhibitory factor (MIF), beta(2)-microglobulin, Niemann pick type C2, secretory leukocyte protease inhibitor, thioredoxin-1, TNF-alpha, tumour protein translationally controlled 1 and ubiquitin. Further, cDNA microarray analysis indicated that the genes for IL-11, TNF receptor 6, TGF-beta receptor 1 and the IFN-gamma receptor were transcribed. CypB, IFN-alpha/beta/gamma, IL-11, IL-25, MIF, TGF-beta and TNF-alpha as well as the known growth factors EGF, IGF-I/II, IL-6, leukaemia inhibitory factor and oncostatin M (OSM) were excluded as involved in autocrine regulation of NS0 cell proliferation. The receptors for TGF-beta, IGF and OSM are however present in NS0 cell membranes since TGF-beta(1) caused cell death, and IGF-I/II and OSM improved cell growth. Even though no ligand was found, the receptor subunit gp130, active in signal transduction of the IL-6 like proteins, was shown to be essential for NS0 cells as demonstrated by siRNA gene silencing.

Zebrafish 17beta-hydroxysteroid dehydrogenases: an evolutionary perspective

The term 17beta-hydroxysteroid dehydrogenase (17beta-HSD) describes an enzyme that stereospecifically reduces or oxidizes a keto- or hydroxy group at C17 of the steroid scaffold, respectively. Fourteen mammalian 17beta-HSDs have been identified so far and nine sequence homologs are found in zebrafish. 17beta-HSDs additionally active in fatty acid metabolism display high sequence conservation and widespread tissue expression. Homologs of these multifunctional 17beta-HSDs have been identified in flies, worms and yeast, and steroid-converting activity was demonstrated in some cases. The "classical" 17beta-HSDs, types 1, 2 and 3, are steroid-specific enzymes expressed in few tissues. They may have arisen at the beginning of vertebrate evolution allowing new, differently controlled modes of steroid hormone action. These findings reflect on two aspects: (1) the evolutionary origin of steroid-specific enzymes and (2) a possible conservation of steroid hormone function in invertebrates through currently unknown mechanisms.

Prolactin receptor-associated protein/17beta-hydroxysteroid dehydrogenase type 7 gene (Hsd17b7) plays a crucial role in embryonic development and fetal survival

Our laboratory has previously cloned and purified a protein named PRAP (prolactin receptor-associated protein) that was shown to be a novel 17beta-hydroxysteroid dehydrogenase (HSD) enzyme with dual activity. This enzyme, renamed HSD17B7 or PRAP/17beta-HSD7, converts estrone to estradiol and is also involved in cholesterol biosynthesis. The major site of its expression is the corpus luteum of a great number of species including rodents and humans. To examine the functional significance of HSD17B7 in pregnancy, we generated a knockout mouse model with targeted deletions of exons 1-4 of this gene. We anticipated a mouse with a severe fertility defect due to its inability to regulate estrogen levels during pregnancy. The heterozygous mutant mice are normal in their development and gross anatomy. The females cycle normally, and both male and female are fertile with normal litter size. To our surprise, the breeding of heterozygous mice yielded no viable HSD17B7 null mice. However, we found HSD17B7 null embryo alive in utero on d 8.5 and d 9.5. By d 10.5, the fetuses grow and suffer from severe brain malformation and heart defect. Because the brain depends on in situ cholesterol biosynthesis for its development beginning at d 10, the major cause of fetal death appears to be due to the cholesterol synthetic activity of this enzyme. By ablating HSD17B7 function, we have uncovered, in vivo, an important requirement for this enzyme during fetal development.

Defined protein and animal component-free NS0 fed-batch culture

A chemically defined protein and animal component-free fed-batch process for an NS0 cell line producing a human IgG(1) antibody has been developed. The fed-batch feed profile was optimised in a step-wise manner. Depletion of measurable compounds was determined by direct analysis. The cellular need for non-measurable compounds was tested by continued culturing of cell suspension, removed from the bioreactor, in shake-flasks supplemented with critical substances. In the final fed-batch culture, 8.4 x 10(6) viable cells mL(-1) and 625 mg antibody L(-1) was obtained as compared to 2.3 x 10(6) cells mL(-1) and 70 mg antibody L(-1) in batch. The increase in cell density, in combination with a prolonged declining phase where antibody formation continued, resulted in a 6.2-fold increase in total cell yield, a 10.5-fold increase in viable cell hours and an 11.4-fold increase in product yield. These improvements were obtained by using a feed with glucose, glutamine, amino acids, lipids, sodium selenite, ethanolamine and vitamins. Specifically, supplementation with lipids (cholesterol) had a drastic effect on the maximum viable cell density. Calcium, magnesium and potassium were not depleted and a feed also containing iron, lithium, manganese, phosphorous and zinc did not significantly enhance the cell yield. The growth and death profiles in the final fed-batch indicated that nutrient deprivation was not the main cause of cell death. The ammonium concentration and the osmolality increased to potentially inhibitory levels, but an imbalance in the supply of growth/survival factors may also contribute to termination of the culture.

Derivation and characterization of cholesterol-independent non-GS NS0 cell lines for production of recombinant antibodies

Presented is an antibody production platform based on the fed-batch culture of recombinant NS0-derived cell lines. NS0 host cells, obtained from the European Collection of Cell Cultures (ECACC, Salisbury, UK, Part No. 85110503), were first adapted to grow in a protein-free, cholesterol-free medium. The resulting host cell line was designated NS0-PFCF (protein-free, cholesterol-free). The five production cell lines presented here were generated using a common protocol consisting of transfection by electroporation and subcloning. The NS0-PFCF host cell line was transfected using a single expression vector containing the Escherichia coli xanthine-guanine phosphoribosyl transferase gene (gpt), and the antibody heavy and light chain genes driven by the CMV promoter. The five cell lines were chosen after one to three rounds of iterative subcloning, which resulted in a 19-64% increase in antibody productivity when four mother-daughter cell pairs were cultured in a fed-batch bioreactor process. The production cell lines were genetically characterized to determine antibody gene integrity, nucleotide sequences, copy number, and the number of insertion sites in the NS0 cell genome. Genetic characterization data indicate that each of the five production cell lines has a single stably integrated copy of the antibody expression vector, and that the antibody genes are correctly expressed. Stability of antibody production was evaluated for three of the five cell lines by comparing the early stage seed bank with the Working Cell Bank (WCB). Antibody productivity was shown to be stable in two of three cell lines evaluated, while one of the cell lines exhibited a 20% drop in productivity after passaging for approximately 4 weeks. These five NS0-derived production cell lines were successfully cultured to produce antibodies with acceptable product quality attributes in a standardized fed-batch bioreactor process, consistently achieving an average specific productivity of 20-60 pg/cell-day, and a volumetric productivity exceeding 120 mg/L-day (Burky et al., 2006). In contrast to the commonly available NS0 host cell line, which requires serum and cholesterol for growth, and the commonly used expression vector system, which uses a proprietary glutamine synthetase selection marker (GS-NS0), these NS0 cells are cholesterol-independent, grow well in a protein-free medium, use a non-proprietary selection marker, and do not require gene amplification for productivity improvement. These characteristics are advantageous for use of this NS0 cell line platform for manufacturing therapeutic antibodies.

Cholesterol delivery to NS0 cells: Challenges and solutions in disposable linear low-density polyethylene-based bioreactors

We report the successful cultivation of cholesterol dependent NS0 cells in linear low-density polyethylene (LLDPE) Wave Bioreactors when employing a low ratio of cyclodextrin to cholesterol additive mixture. While cultivation of NS0 cells in Wave Bioreactors was successful when using a culture medium supplemented with fetal bovine serum (FBS), cultivation with the same culture medium supplemented with cholesterol-lipid concentrate (CLC), which contains lipids and synthetic cholesterol coupled with the carrier methyl-beta-cyclodextrin (mbetaCD), proved to be problematic. However, it was possible to cultivate NS0 cells in the medium supplemented with CLC when using conventional cultivation vessels such as disposable polycarbonate shake-flasks and glass bioreactors. A series of experiments investigating the effect of the physical conditions in Wave Bioreactors (e.g., rocking rate/angle, gas delivery mode) ruled out their likely influence, while the exposure of the cells to small squares of Wave Bioreactor film resulted in a lack of growth as in the Wave Bioreactor, suggesting an interaction between the cells, the CLC, and the LLDPE contact surface. Further experiments with both cholesterol-independent and cholesterol-dependent NS0 cells established that the concurrent presence of mbetaCD in the culture medium and the LLDPE film was sufficient to inhibit growth for both cell types. By reducing the excess mbetaCD added to the culture medium, it was possible to successfully cultivate cholesterol-dependent NS0 cells in Wave Bioreactors using a cholesterol-mbetaCD complex as the sole source of exogenous cholesterol. We propose that the mechanism of growth inhibition involves the extraction of cholesterol from cell membranes by the excess mbetaCD in the medium, followed with the irreversible adsorption or entrapment of the cholesterol-mbetaCD complexes to the LLDPE surface of the Wave Bioreactor. Controlling and mitigating these negative interactions enabled the routine utilization of disposable bioreactors for the cultivation of cholesterol-dependent NS0 cell lines in conjunction with an animal component-free cultivation medium.

Multifunctionality of human 17beta-hydroxysteroid dehydrogenases

17Beta-hydroxysteroid dehydrogenases (17beta-HSDs) belong to the family of short chain dehydrogenases/reductases (SDRs) and aldoketo-reductases (AKRs). Some of the enzymes were discovered and named due to their enzymatic activity on steroid substrates or according to their sequence homology to other 17beta-HSDs. During characterisation of these enzymes it turned out that their substrate specificity is broader than first expected and key functions of some 17beta-HSDs in vivo are probably not in steroid metabolism but in basic metabolic pathways. The issue of such multifunctionality is the topic of this review.

Engineering cells for cell culture bioprocessing--physiological fundamentals

In the past decade, we have witnessed a tremendous increase in the number of mammalian cell-derived therapeutic proteins with clinical applications. The success of making these life-saving biologics available to the public is partly due to engineering efforts to enhance process efficiency. To further improve productivity, much effort has been devoted to developing metabolically engineered producing cells, which possess characteristics favorable for large-scale bioprocessing. In this article we discuss the fundamental physiological basis for cell engineering. Different facets of cellular mechanisms, including metabolism, protein processing, and the balancing pathways of cell growth and apoptosis, contribute to the complex traits of favorable growth and production characteristics. We present our assessment of the current state of the art by surveying efforts that have already been undertaken in engineering cells for a more robust process. The concept of physiological homeostasis as a key determinant and its implications on cell engineering is emphasized. Integrating the physiological perspective with cell culture engineering will facilitate attainment of dream cells with superlative characteristics.