Detection of endoplasmic reticulum stress markers and production enhancement treatments in transgenic goats expressing recombinant human butyrylcholinesterase

Design and production strategies for developing a recombinant butyrylcholinesterase medical countermeasure for Organophosphorus poisoning

Organophosphorus nerve agents represent a serious chemical threat due to their ease of production and scale of impact. The recent use of the nerve agent Novichok has re-emphasised the need for broad-spectrum medical countermeasures (MCMs) to these agents. However, current MCMs are limited. Plasma derived human butyrylcholinesterase (huBChE) is a promising novel bioscavenger MCM strategy, but is prohibitively expensive to isolate from human plasma at scale. Efforts to produce recombinant huBChE (rBChE) in various protein expression platforms have failed to achieve key critical attributes of huBChE such as circulatory half-life. These proteins often lack critical features such as tetrameric structure and requisite post-translational modifications. This review evaluates previous attempts to generate rBChE and assesses recent advances in mammalian cell expression and protein engineering strategies that could be deployed to achieve the required half-life and yield for a viable rBChE MCM. This includes the addition of a proline-rich attachment domain, fusion proteins, post translational modifications, expression system selection and optimised downstream processes. Whilst challenges remain, a combinatorial approach of these strategies demonstrates potential as a technically feasible approach to achieving a bioactive and cost effective bioscavenger MCM.

Structure and therapeutic uses of butyrylcholinesterase: Application in detoxification, Alzheimer's disease, and fat metabolism

Structural information of butyrylcholinesterase (BChE) and its variants associated with several diseases are discussed here. Pure human BChE has been proved safe and effective in treating organophosphorus (OPs) poisoning and has completed Phase 1 and 2 pharmacokinetic (PK) and safety studies. The introduction of specific mutations into native BChE to endow it a self-reactivating property has gained much progress in producing effective OPs hydrolases. The hydrolysis ability of native BChE on cocaine has been confirmed but was blocked to clinical application due to poor PK properties. Several BChE mutants with elevated cocaine hydrolysis activity were published, some of which have shown safety and efficiency in treating cocaine addiction of human. The increased level of BChE in progressed Alzheimer's disease patients made it a promising target to elevate acetylcholine level and attenuate cognitive status. A variety of selective BChE inhibitors with high inhibitory activity published in recent years are reviewed here. BChE could influence the weight and insulin secretion and resistance of BChE knockout (KO) mice through hydrolyzing ghrelin. The BChE-ghrelin pathway could also regulate aggressive behaviors of BChE-KO mice.

Symposium review: Determinants of milk production: Understanding population dynamics in the bovine mammary epithelium

The mammary gland undergoes distinct periods of growth, development, and secretory activity. During bovine lactation, a gradual decrease in the number of mammary epithelial cells largely accounts for the decline in milk production with advancing lactation. The net decline in cell number (approx. 50%) is due to cell death but is simultaneously accompanied by cell renewal. Although the rate of cell proliferation is slow, by the end of lactation most cells in the gland were formed after calving. Typically milking is terminated when cows are in the final 2 mo of pregnancy. This causes regenerative involution, wherein extensive cell replacement and mammary growth occurs. We hypothesized that replacement of senescent secretory cells and progenitor cells during the dry period increases milk yield in the next lactation. Analysis of global gene expression revealed networks and canonical pathways during regenerative involution that support cell turnover and mammary growth, and reflect oxidative stress, mitochondrial dysfunction, and endoplasmic reticulum (ER) stress. Immune responses consistent with influx of neutrophils, macrophages, and lymphocytes, and processes that support mammary differentiation and lactogenesis were also evident. Data also suggest that replication of stem and progenitor cells occurs during the dry period. Relying on long-term retention of bromodeoxyuridine-labeled DNA, we identified putative bovine mammary stem cells. These label-retaining epithelial cells (LREC) are in low abundance within mammary epithelium (<1%), predominantly estrogen receptor-negative, and localized in a basal or suprabasal layer of the epithelium. Analyses of gene expression in laser-microdissected LREC are consistent with the concept that LREC represent stem cells and progenitor cells, which differ in properties and location within the epithelial layer. We identified potential markers for these cells and have increased their number by infusing xanthosine through the teat canal of prepubertal heifers. Altering population dynamics of mammary stem and progenitor cells during the mammary cycle may be a means to increase efficiency of milk production.

Evaluation of xanthosine treatment on gene expression of mammary glands in early lactating goats

This study examined the hypothesis that xanthosine (XS) treatment would promote mammary-specific gene expression and stem cell transcripts and have a positive influence on milk yield of dairy goats. Seven primiparous Beetal goats were assigned to the study. Five days after kidding, one gland (either left or right) was infused with XS (TRT) twice daily for 3 d and the other gland with no XS infusion served as a control (CON). Mammary biopsies were collected at 10 d and RNA was isolated. Gene expression analysis of milk synthesis genes, mammary stem/progenitor cell markers, cell proliferation and differentiation markers were performed using real time quantitative PCR (RT-qPCR). Results showed that the transcripts of milk synthesis genes (BLG4, CSN2, LALBA, FABP3, CD36) and mammary stem/progenitor cell markers (ALDH1 and NR5A2) were increased in as a result of XS treatment. Average milk yield in TRT glands was increased marginally (approximately ~2% P = 0·05, paired t-test) per gland relative to CON gland until 7 wk. After 7 wk, milk yield of TRT and CON glands did not differ. Analysis of milk composition revealed that protein, lactose, fat and solids-not-fat percentages remained the same in TRT and CON glands. These results suggest that XS increases expression of milk synthesis genes, mammary stem/progenitor cells and has a small effect on milk yield.

In vivo response of xanthosine on mammary gene expression of lactating Beetal goat

Xanthosine is hypothesized to increase stem cell number by promoting symmetrical cell division. Stem cells, in particular mammary stem/progenitor cells are important for gland growth and tissue repair. Molecular mechanism of xanthosine effects on mammary tissue is very limited therefore, a detailed study is warranted. The objective of this study was to evaluate transcriptomic changes in mammary gland infused/not infused with xanthosine of lactating goat. Seven primiparous Beetal goats on day 5 after kidding, were selected for the study. One gland of each goat was infused with xanthosine (TRT gland) twice daily for 3 days while the other gland did not receive any xanthosine and served as control (CON gland). Biopsy of mammary tissues was taken from TRT and CON glands, 2 days after the last day of treatment that is on day 10 after kidding. Illumina RNA-sequencing (RNA-seq) was performed for global gene expression analysis of contralateral glands. Of 382 differentially expressed genes (DEGs), 372 genes were annotated to the goat genome. Gene ontology analyses revealed majority of the DEGs to be associated with metabolic pathways (glycan and lipid metabolism), biosynthesis of antibiotics and peroxisome proliferator-activated receptor signalling pathways. These molecular pathways are either directly or indirectly involved with lipid metabolism in mammary tissue and host adaptive immune response. Expression of stem cell marker namely aldehyde dehydrogenase enzymes (ALDH1A1, ALDH3B1) were upregulated in the treatment gland. Real-time quantitative PCR (RT-qPCR) analyses of selected DEGs showed their expression profiles to be in agreement with results of RNA-seq. To our knowledge, this is the first study that describes effects of xanthosine on transcriptomic changes of mammary tissue. This information can be used further to dissect the molecular mechanisms underlying effects of xanthosine to improve production potential and udder health.

Examination of the xanthosine response on gene expression of mammary epithelial cells using RNA-seq technology

BACKGROUND

Xanthosine treatment has been previously reported to increase mammary stem cell population and milk production in cattle and goats. However, the underlying molecular mechanisms associated with the increase in stem cell population and milk production remain unclear.

METHODS

Primiparous Beetal goats were assigned to the study. Five days post-partum, one mammary gland of each goat was infused with xanthosine (TRT) twice daily (2×) for 3 days consecutively, and the other gland served as a control (CON). Milk samples from the TRT and CON glands were collected on the 10th day after the last xanthosine infusion and the total RNA was isolated from milk fat globules (MEGs). Total RNA in MFGs was mainly derived from the milk epithelial cells (MECs) as evidenced by expression of milk synthesis genes. Significant differentially expressed genes (DEGs) were subjected to Gene Ontology (GO) terms using PANTHER and gene networks were generated using STRING db.

RESULTS

Preliminary analysis indicated that each individual goat responded to xanthosine treatment differently, with this trend being correlated with specific DEGs within the same animal's mammary gland. Several pathways are impacted by these DEGs, including cell communication, cell proliferation and anti-microbials.

CONCLUSIONS

This study provides valuable insights into transcriptomic changes in milk producing epithelial cells in response to xanthosine treatment. Further characterization of DEGs identified in this study is likely to delineate the molecular mechanisms of increased milk production and stem or progenitor cell population by the xanthosine treatment.

Alpha-ketoglutarate enhances milk protein synthesis by porcine mammary epithelial cells

Alpha-ketoglutarate (AKG), a key intermediate in the Krebs cycle, has been reported to promote protein synthesis through activating mechanistic targeting of rapamycin (mTOR) in enterocytes. The study tested the hypothesis that AKG may enhance growth and milk protein synthesis in porcine mammary epithelial cells (PMECs). PMECs were cultured for 96 h in Dulbecco's modified Eagle's-F12 Ham medium (DMEM-F12) containing prolactin (2 µg/ml) and AKG (0 or 1.5 mM). At the end of 96-h culture, the abundance of apoptosis-related proteins (caspase-3, caspase-9), milk-specific proteins (α-lactalbumin and β-casein), mTOR signaling proteins (mTOR, p-mTOR, PERK, p-PERK, eIF2a, P70S6K and p-P70S6K), and endoplasmic reticulum stress (ERS)-associated proteins (BiP and CHOP) in PMEC were determined. Addition of AKG dose-dependently enhanced cell viability in the absence or presence of prolactin, with optimal concentrations of AKG being at 1.0 and 1.5 mM, respectively. In the presence of prolactin, addition of 1.5 mM AKG: (1) decreased (P < 0.05) the abundance of caspase-3 and caspase-9 by 21 and 39 %; (2) enhanced (P < 0.05) the phosphorylation of p-mTOR and p-P70S6K by 39 and 89 %, respectively; (3) increased (P < 0.05) the production of β-casein and α-lactalbumin by 16 and 20 %, respectively; (4) attenuated (P < 0.05) the expression of CHOP by 34 % but promoted (P < 0.05) the expression of BiP by 46 %; (5) increased (P < 0.05) the secretion of lactose by 15 %, when compared to the 0 mM AKG group. Rapamycin (50 nM; an inhibitor of mTOR) attenuated (P < 0.05) the stimulatory effect of AKG on mTOR signaling and syntheses of milk protein and lactose, while relieving (P < 0.05) an inhibitory effect of AKG on expression of proteins related to ERS. Collectively, our results indicate that AKG enhances milk protein production by modulating mTOR and ERS signaling pathways in PMECs.

Mammary stem cells: expansion and animal productivity

Identification and characterization of mammary stem cells and progenitor cells from dairy animals is important in the understanding of mammogenesis, tissue turnover, lactation persistency and regenerative therapy. It has been realized by many investigators that altered lactation, long dry periods (non-milking period between two consecutive lactation cycles), abrupt cessation of lactation (common in water buffaloes) and disease conditions like mastitis, greatly reduce milk yield thus render huge financial losses within the dairy sector. Cellular manipulation of specialized cell types within the mammary gland, called mammary stem cells (MaSCs)/progenitor cells, might provide potential solutions to these problems and may improve milk production. In addition, MaSCs/progenitor cells could be used in regenerative therapy against tissue damage caused by mastitis. This review discusses methods of MaSC/progenitor cell manipulation and their mechanisms in bovine and caprine animals. Author believes that intervention of MaSCs/progenitor cells could lessen the huge financial losses to the dairy industry globally.

Progress in the development of enzyme-based nerve agent bioscavengers

Acetylcholinesterase is the physiological target for acute toxicity of nerve agents. Attempts to protect acetylcholinesterase from phosphylation by nerve agents, is currently achieved by reversible inhibitors that transiently mask the enzyme active site. This approach either protects only peripheral acetylcholinesterase or may cause side effects. Thus, an alternative strategy consists in scavenging nerve agents in the bloodstream before they can reach acetylcholinesterase. Pre- or post-exposure administration of bioscavengers, enzymes that neutralize and detoxify organophosphorus molecules, is one of the major developments of new medical counter-measures. These enzymes act either as stoichiometric or catalytic bioscavengers. Human butyrylcholinesterase is the leading stoichiometric bioscavenger. Current efforts are devoted to its mass production with care to pharmacokinetic properties of the final product for extended lifetime. Development of specific reactivators of phosphylated butyrylcholinesterase, or variants with spontaneous reactivation activity is also envisioned for rapid in situ regeneration of the scavenger. Human paraoxonase 1 is the leading catalytic bioscavenger under development. Research efforts focus on improving its catalytic efficiency toward the most toxic isomers of nerve agents, by means of directed evolution-based strategies. Human prolidase appears to be another promising human enzyme. Other non-human efficient enzymes like bacterial phosphotriesterases or squid diisopropylfluorophosphatase are also considered though their intrinsic immunogenic properties remain challenging for use in humans. Encapsulation, PEGylation and other modifications are possible solutions to address this problem as well as that of their limited lifetime. Finally, gene therapy for in situ generation and delivery of bioscavengers is for the far future, but its proof of concept has been established.

Comparative aspects of mammary gland development and homeostasis

Mammary glands are crucial to the reproductive strategy of mammals, and the milk of domesticated ruminants serves as an important source of nutrients for the human population. The majority of mammary gland development occurs postnatally, and the mammary gland undergoes cyclical periods of growth, differentiation, lactation, and regression that are coordinated to provide nutrients for offspring or are driven by strategies to manage reproduction and milk production of domesticated species. Growth and maintenance of the mammary epithelium depends on the function of mammary stem cells and progenitor cells. In this review, we provide an overview of postnatal mammary gland development, cyclical phases of mammary gland regression (regression during lactation and between successive lactations), and mammary stem cells and progenitor cells. Where possible, these processes are related to animal production and compared across species, particularly bovine, porcine, murine, and human.

In vitro expansion of the mammary stem/progenitor cell population by xanthosine treatment

BACKGROUND

Mammary stem cells are critical for growth and maintenance of the mammary gland and therefore are of considerable interest for improving productivity and efficiency of dairy animals. Xanthosine treatment has been demonstrated to promote expansion of putative mammary stem cells in vivo, and hepatic and hair follicle stem cells in vitro. In the latter, xanthosine promoted the symmetrical division of hepatic and hair follicle stem cells. The objective of this study was to determine if treating primary cultures of bovine mammary epithelial cells (MEC) with xanthosine increases the stem/progenitor cell population by promoting symmetrical division of mammary stem cells.

RESULTS

In vitro treatment with xanthosine increased the population of MEC during the exponential phase of cell growth, reducing the doubling time from 86 h in control cultures to 60 h in xanthosine-treated cultures. The bromodeoxyuridine (BrdU) labeling index and the proportion of MEC in S-phase both were increased by xanthosine treatment, indicating that increased cell accretion was due to increased cell proliferation. Analysis of daughter-pairs indicated that xanthosine promoted a shift from asymmetric to symmetric cell division. Moreover, the 30 % increase in symmetric cell division was concomitant with an increase in the proportion of MEC that were positive for a putative stem cell marker (FNDC3B) and a trend toward increased telomerase activity. These results suggest that xanthosine treatment in vitro can increase cell proliferation, promote symmetric cell division and enhance stem/progenitor cell activity.

CONCLUSIONS

Xanthosine treatment increased the proliferation rate of bovine MEC in vitro. This was likely to be mediated by an increase in the proportion of stem/progenitor cells in the MEC population due to promotion of symmetrical stem cell division by xanthosine.