Improved yields of full-length functional human FGF1 can be achieved using the methylotrophic yeast Pichia pastoris

Recombinant bovine FGF1 promotes muscle satellite cells mitochondrial fission and proliferation in serum-free conditions

Cell cultured meat is a novel and promising technology, but developing specific culture medium for muscle cells remains one of the main technical obstacles. FGF1 signaling is reported to promote proliferation and maintain proliferative capacity of satellite cells. However, the effect of FGF1 as a supplement to serum-free medium on satellite cells in vitro culture is still unclear. In this study, an efficient method for the production of soluble and biologically active recombinant bovine FGF1 (rbFGF1) protein in Escherichia coli was established. The soluble expression level of TrxA-rbFGF1 fusion protein was 562 mg/L in shake flasks, resulting in 5.5 mg of pure rbFGF1 from 0.1 L of starting culture. In serum-free culture conditions, rbFGF1 effectively promoted the proliferation and regulated the mitochondrial morphology and function of C2C12 myoblasts.rbFGF1 activated extracellular signal-regulated kinases1/2 (ERK1/2) signaling in C2C12 myoblasts, which further stimulated dynamin related protein 1 (DRP1) Ser616 phosphorylation. These findings highlighted the potential application of rbFGF1 in developing effective serum-free medium for cultured meat production.

Optimization of the extraction conditions and dermal toxicity of oil body fused with acidic fibroblast growth factor (OLAF)

INTRODUCTION

Oil body (OB), a subcellular organelle that stores oil in plant seeds, is considered a new transdermal drug delivery system. With the increasing understanding of the OB and its main protein (oleosin), numerous studies have been conducted on OB as "carrier" for the expression of exogenous proteins. In our previous study, oil body fused with aFGF (OLAF) was obtained using a plant oil body expression system that had been preliminarily proven to be effective in accelerating the healing of skin wounds. However, no dermal toxicological information on OLAF is available.

OBJECTIVE

To ensure the dermal safety of OLAF, a series of tests (the acute dermal toxicity test, 21-day repeat dermal toxicity test, dermal irritation test and skin sensitisation test) were conducted after optimising the extraction protocol of OLAF.

MATERIALS AND METHODS

To improve the extraction rate of OLAF, response surface methodology (RSM) was first employed to optimise the extraction conditions. Then, Wistar rats were exposed to OLAF (400 mg·kg^-1 body weight) in two different ways (6 hours/time for 24 hours and 1 time/day for 21 days) to evaluate the acute dermal toxicity and 21-day repeated dermal toxicity of OLAF. In the acute dermal toxicity test, clinical observations were conducted to evaluate the toxicity, behaviour, and health of the animals for 14 consecutive days. Similarly, the clinical signs, body weight, haematological and biochemical parameters, histopathological changes and other indicators were also detected during the 21 days administration. For the dermal irritation test, single and multiple doses of OLAF (125 mg·kg^-1 body weight) were administered to albino rabbits for 14 days (1 time/day). The irritation reaction on the skin of each albino rabbit was recorded and scored. Meanwhile, skin sensitisation to OLAF was conducted using guinea pigs for a period of 28 days.

RESULTS

Suitable extraction conditions for OLAF (PBS concentration 0.01, pH of PBS 8.6, solid-liquid ratio 1:385 g·mL^-1) were obtained using RSM. Under these conditions, the extraction rate and particle size of OLAF were 7.29% and 1290 nm, respectively. In the tests of acute dermal toxicity and 21-day repeated dermal toxicity, no mortality or significant differences were observed in terms of clinical signs, body weight, haematological parameters, biochemical parameters and anatomopathological analysis. With respect to the dermal irritation test and skin sensitisation test, no differences in erythema, oedema or other abnormalities were observed between treatment and control groups on gross and histopathological examinations.

CONCLUSIONS

The results of this study suggest that OLAF does not cause obvious toxicity, skin sensitisation or irritation in animals.

Large-Scale Preparation of Highly Stable Recombinant Human Acidic Fibroblast Growth Factor in Escherichia coli BL21(DE3) plysS Strain

In this study, the optimum human aFGF gene encoding haFGF₁₃₅ was cloned in pET3c and transferred to Escherichia coli BL21(DE3) plysS. To enhance the yield of fermentation and the expression level of the target protein, the fermentation parameters, including temperature, pH, dissolved oxygen, glucose concentration, ammonium chloride concentration, induction time, and inducer (IPTG) concentration, were optimized. The optimized fermentation parameters were used in large-scale fermentation (30 L). Ion-exchange and heparin-affinity column chromatography techniques were used for separation and purification of rhaFGF₁₃₅ protein. HPLC, isoelectric focusing electrophoresis, and mass spectrometry were used to detect the purity, isoelectric point, and molecular weight and peptide map of rhaFGF₁₃₅ protein, respectively. Mitogenic activity of rhaFGF₁₃₅ protein was detected in NIH-3T3 cells and a full-thickness injury wound diabetic rat model. The production and expression level of rhaFGF₁₃₅ in the 30-L scale fermentation reached 80.4 ± 2.7 g/L culture and 37.8% ± 1.8%, respectively. The RP-HPLC and SDS-PAGE purity of the final rhaFGF₁₃₅ product almost reached 100%, and the final pure protein yield was 158.6 ± 6.8 mg/L culture. Finally, the cell and animal experiments showed that rhaFGF₁₃₅ retained a potent mitogenic activity. The large-scale process of rhaFGF₁₃₅ production reported herein is relatively stable and time-saving, and thus, it can be used as an efficient and economic strategy for the synthesis of rhaFGF₁₃₅ at the industrial level.

Efficient Soluble Expression and Purification of Recombinant Human Acidic Fibroblast Growth Factor from Escherichia coli via Fusion with a Novel Collagen-like Protein Scl2

Human acidic fibroblast growth factor (haFGF) is a multifunctional protein involved in regulating a wide range of cellular processes. As a potent therapeutic agent, it is highly desirable to produce recombinant haFGF (r-haFGF) at low cost. However, the complex structure and formation of aggregation confines its high-level soluble expression and functional form. Herein, to produce r-haFGF efficiently in E. coli, we devised a novel soluble expression and cost-effective purification approach based on fusion with Scl2-M (a novel modified collagen-like protein) for the first time. By using this strategy, more than 95% of the Scl2-M-haFGF fusion protein was highly expressed in soluble form and the expression level of targeted fusion protein in shake flasks and 5-L fermenter was 0.42 g/L and 2.28 g/L, respectively. Subsequently, the recombinant Scl2-M-haFGF was readily purified through a facile process of acid precipitation and subjected to enterokinase (EK) cleavage. After Scl2-M cleavage, tag-free r-haFGF was further purified using ion-exchange chromatography. The recovery rate of the whole purification process attained 34.2%. Furthermore, the resulting high-purity (96.0%) r-haFGF was prepared by freeze-drying as a final product, and its bioactivity was confirmed to potentiate the proliferation of L929 and BALB-3T3 fibroblasts. Overall, our developed method has the potential for the massive production of the r-haFGF in the future.

Identification of sugar response complex in the metallothionein OsMT2b gene promoter for enhancement of foreign protein production in transgenic rice

A 146-bp sugar response complex MTSRC is identified in the promoter of rice metallothionein OsMT2b gene conferring high-level expression of luciferase reporter gene and bioactive recombinant haFGF in transgenic rice. A rice subfamily type 2 plant metallothionein (pMT) gene, OsMT2b, encoding a reactive oxygen species (ROS) scavenger protein, has been previously shown to exhibit the most abundant gene expression in young rice seedling. Expression of OsMT2b was found to be regulated negatively by ethylene and hydrogen peroxide in rice stem node under flooding stress, but little is known about its response to sugar depletion. In this study, transient expression assay and transgenic approach were employed to characterize the regulation of the OsMT2b gene expression in rice. We found that the expression of OsMT2b gene is induced by sugar starvation in both rice suspension cells and germinated embryos. Deletion analysis and functional assay of the OsMT2b promoter revealed that the 5'-flanking region of the OsMT2b between nucleotides - 351 and - 121, which contains the sugar response complex (- 266 to - 121, designated MTSRC) is responsible for high-level promoter activity under sugar starvation. It was also found that MTSRC significantly enhances the Act1 promoter activity in transgenic rice cells and seedlings. The modified Act1 promoter, Act1-MTSRC, was used to produce the recombinant human acidic fibroblast growth factor (haFGF) in rice cells. Our result shows that the bioactive recombinant haFGF is stably produced in transformed rice cell culture and yields are up to 2% of total medium proteins. Our studies reveal that MTSRC serves as a strong transcriptional activator and the Act1-MTSRC promoter can be applicable in establishing an efficient expression system for the high-level production of foreign proteins in transgenic rice cells and seedlings.

SHuffle™ T7 strain is capable of producing high amount of recombinant human fibroblast growth factor-1 (rhFGF-1) with proper physicochemical and biological properties

BACKGROUND

Human fibroblast growth factor-1 (FGF-1) has powerful mitogenic activities in a variety of cell types and plays significant roles in many physiological processes e.g. angiogenesis and wound healing. There is increasing demand for large scale production of recombinant human FGF-1 (rhFGF-1), in order to investigate the potential medical use. In the present study, we explored SHuffle™ T7 strain for production of rhFGF-1.

METHODS

A synthetic gene encoding Met-140 amino acid form of human FGF-1 was utilized for expression of the protein in three different E. coli hosts (BL21 (DE3), Rosetta-gami™ 2(DE3), SHuffle™ T7). Total expressions and soluble/insoluble expression ratios of rhFGF-1 in different hosts were analyzed and compared. Soluble rhFGF-1 produced in SHuffle™ T7 cells was purified using one-step heparin-Sepharose affinity chromatography and characterized by a variety of methods for physicochemical and biological properties.

RESULTS

The highest level of rhFGF-1 expression and maximum soluble/insoluble ratio were achieved in SHuffle™ T7 strain. Using a single-step heparin-Sepharose chromatography, about 1500mg of purified rhFGF-1 was obtained from one liter of the culture, representing purification yield of ∼70%. The purified protein was reactive toward anti-FGF-1 ployclonal antibody in immunoblotting. Mass spectrometry confirmed the protein had expected amino acid sequence and molecular weight. In reverse-phase high-performance liquid chromatography (RP-HPLC), the protein displayed the same retention time with the human FGF-1 standard, and purity of 94%. Less than 0.3% of the purified protein was comprised of oligomers and/or aggregates as judged by high-performance size-exclusion chromatography (HP-SEC). Secondary and tertiary structures of the protein, investigated by circular dichroism and intrinsic fluorescence spectroscopy methods, respectively, represented native folding of the protein. The purified rhFGF-1 was bioactive and stimulated proliferation of NIH 3T3 cells with EC50 of 0.84ng/mL.

CONCLUSION

Although SHuffle™ T7 has been introduced for production of disulfide-bonded proteins in cytoplasm, we herein successfully recruited it for high yield production of soluble and bioactive rhFGF-1, a protein with 3 free cysteine and no disulfide bond. To our knowledge, this is the highest-level of rhFGF-1 expression in E. coli reported so far. Extensive physicochemical and biological analysis showed the protein had similar characteristic to authentic FGF-1.

Large-scale production of bioactive recombinant human acidic fibroblast growth factor in transgenic silkworm cocoons

With an increasing clinical demand for functional therapeutic proteins every year, there is an increasing requirement for the massive production of bioactive recombinant human acidic fibroblast growth factor (r-haFGF). In this present study, we delicately explore a strategy for the mass production of r-haFGF protein with biological activity in the transgenic silkworm cocoons. The sequence-optimized haFGF was inserted into an enhanced sericin-1 expression system to generate the original transgenic silkworm strain, which was then further crossed with a PIG jumpstarter strain to achieve the remobilization of the expression cassette to a “safe harbor” locus in the genome for the efficient expression of r-haFGF. In consequence, the expression of r-haFGF protein in the mutant line achieved a 5.6-fold increase compared to the original strain. The high content of r-haFGF facilitated its purification and large-scald yields. Furthermore, the r-haFGF protein bioactively promoted the growth, proliferation and migration of NIH/3T3 cells, suggesting the r-haFGF protein possessed native mitogenic activity and the potential for wound healing. These results show that the silk gland of silkworm could be an efficient bioreactor strategy for recombinant production of bioactive haFGF in silkworm cocoons.

Ectopic expression of human acidic fibroblast growth factor 1 in the medicinal plant, Salvia miltiorrhiza, accelerates the healing of burn wounds

Background

Healing of burns is a complex process and very few effective treatments exist to facilitate the burn recovery process. Human acidic fibroblast growth factor 1 (FGF-1) plays an important role in a variety of biological processes, including angiogenesis, and tissue repair. Salvia miltiorrhiza is widely used in traditional Chinese medicine as an herb for the treatment of various diseases, including cardiovascular and cerebrovascular diseases, and traumatic injuries. We present that expression of FGF-1 in S. miltiorrhiza significantly accelerates the healing of burn wounds.

Results

The human fgf-1 gene was fused with a barley α-amylase signal peptide DNA sequence and driven by a 35S promoter for constitutive expression in transgenic S. miltiorrhiza plants. The highest yield of recombinant FGF-1 obtained from leaves of transgenic S. miltiorrhiza lines was 272 ng/fresh weight. Aqueous extracts from transgenic S. miltiorrhiza exhibited FGF-1 activity approximately 19.2-fold greater than that of the standard FGF-1. Compared to the standard FGF-1 or the extracts obtained from non-transgenic plants, it stimulated proliferation of Balb/c 3 T3 mouse fibroblast cells assessed with the standard MTT assay and promoted angiogenesis in the chicken embryo chorioallantoic membrane (CAM) assay. Topical application of the extract significantly accelerated the burn wound healing process.

Conclusions

The product appears to retain the biological activity of both FGF-1 as well as the medicinal properties of the plant. The extracts from transgenic S. miltiorrhiza combines the therapeutic functions of FGF-1 and the medicinal plant, S. miltiorrhiza. Topical application of the product can reduce the costs associated with extraction, purification, and recovery.

Preparation of Pichia pastoris expression plasmids

When planning any heterologous expression experiment, the very first critical step is related to the design of the overall strategy, hence to the selection of the most adapted expression vector. The very flexible Pichia pastoris system offers a broad range of possibilities for the production of secreted, endogenous or membrane proteins thanks to a combination of various plasmid backbones, selection markers, promoters and fusion sequences introduced into dedicated host strains. The present chapter provides some guidelines on the choice of expression vectors and expression strategies. It also brings the reader a complete toolbox from which plasmids and fusion sequences can be picked and assembled to set up appropriate expression vectors. Finally, it provides standard starting protocols for the preparation of the selected plasmids and their use for host strain transformation.

Insight into factors directing high production of eukaryotic membrane proteins; production of 13 human AQPs in Pichia pastoris

Membrane proteins are key players in all living cells. To achieve a better understanding of membrane protein function, significant amounts of purified protein are required for functional and structural analyses. Overproduction of eukaryotic membrane proteins, in particular, is thus an essential yet non-trivial task. Hence, improved understanding of factors which direct a high production of eukaryotic membrane proteins is desirable. In this study we have compared the overproduction of all human aquaporins in the eukaryotic host Pichia pastoris. We report quantitated production levels of each homologue and the extent of their membrane localization. Our results show that the protein production levels vary substantially, even between highly homologous aquaporins. A correlation between the extents of membrane insertion with protein function also emerged, with a higher extent of membrane insertion for pure water transporters compared to aquaporin family members with other substrate specificity. Nevertheless, the nucleic acid sequence of the second codon appears to play an important role in overproduction. Constructs containing guanine at the first position of this codon (being part of the mammalian Kozak sequence) are generally produced at a higher level, which is confirmed for hAQP8. In addition, mimicking the yeast consensus sequence (ATGTCT) apparently has a negative influence on the production level, as shown for hAQP1. Moreover, by mutational analysis we show that the yield of hAQP4 can be heavily improved by directing the protein folding pathway as well as stabilizing the aquaporin tetramer.

Exceptional overproduction of a functional human membrane protein

Eukaryotic--especially human--membrane protein overproduction remains a major challenge in biochemistry. Heterologously overproduced and purified proteins provide a starting point for further biochemical, biophysical and structural studies, and the lack of sufficient quantities of functional membrane proteins is frequently a bottleneck hindering this. Here, we report exceptionally high production levels of a correctly folded and crystallisable recombinant human integral membrane protein in its active form; human aquaporin 1 (hAQP1) has been heterologously produced in the membranes of the methylotrophic yeast Pichia pastoris. After solubilisation and a two step purification procedure, at least 90 mg hAQP1 per liter of culture is obtained. Water channel activity of this purified hAQP1 was verified by reconstitution into proteoliposomes and performing stopped-flow vesicle shrinkage measurements. Mass spectrometry confirmed the identity of hAQP1 in crude membrane preparations, and also from purified protein reconstituted into proteoliposomes. Furthermore, crystallisation screens yielded diffraction quality crystals of untagged recombinant hAQP1. This study illustrates the power of the yeast P. pastoris as a host to produce exceptionally high yields of a functionally active, human integral membrane protein for subsequent functional and structural characterization.