Recombinant expression of biologically active rat leptin in Escherichia coli

The 14th Ile residue is essential for Leptin function in regulating energy homeostasis in rat

LEPTIN (LEP) is a circulating hormone released primarily from white adipocytes and is crucial for regulating satiety and energy homeostasis in humans and animals. Using the CRISPR technology, we created a set of Lep mutant rats that carry either null mutations or a deletion of the 14(th) Ile (LEP(∆I14)) in the mature LEP protein. We examined the potential off-target sites (OTS) by whole-genome high-throughput sequencing and/or Sanger-sequencing analysis and found no OTS in mutant rats. Mature LEP(∆I14) is incessantly produced and released to blood at a much elevated level due to the feedback loop. Structure modeling of binding conformation between mutant LEP(∆I14) and LEPTIN receptor (LEPR) suggests that the conformation of LEP(∆I14) impairs its binding with LEPR, consistent with its inability to activate STAT3-binding element in the luciferase reporter assay. Phenotypic study demonstrated that Lep(∆I14) rats recapitulate phenotypes of Lep-null mutant rats including obesity, hyperinsulinemia, hepatic steatosis, nephropathy, and infertility. Compared to the existing ob/ob mouse models, this Lep(∆I14/∆I14) rat strain provides a robust tool for further dissecting the roles of LEP in the diabetes related kidney disease and reproduction problem, beyond its well established function in regulating energy homeostasis.

In vivo effects of leptin on lymphocyte subpopulations in mice

Leptin, a hormone-cytokine mainly produced by the adipose tissue, has pleitropic effects on many biological system including metabolic, endocrine, and immune system. Although it is well known that leptin controls food intake on hypothalamic regions of brain, the role of leptin in hematopoietic and immune processes has been mainly investigated with in vitro and transgenic mouse studies. The aim of this study was to investigate the effects of peripheral leptin on lymphocyte subpopulation. Initially forty male Swiss albino mice were divided into five groups. Mice in group I (Control) were given serum physiologic (SP) and group L100, group L250, group L500, and group L1000 were given 100, 250, 500 and 1000 μg/kg/day recombinant mouse leptin, respectively. Leptin or SP was injected subcutaneously for the next 6 days. Daily food/water intake was recorded for each group. At the end of the study, whole blood samples (500 μl) were obtained via intracardiac punction in anesthetized mice. Leptin levels and lymphocyte subpopulations in blood samples were analyzed. We show that no in vivo dose-dependent effect of leptin is existed on lymphocyte subpopulations count in mice. Treatment of mice with high-dose leptin led to increase only CD4+ cells (P<0.05). In addition, high-dose leptin slightly increased CD3+ cells but this was not statistically confirmed (P=0.08). Notably, it was found that leptin caused insignificant changes on body weight and food intake in normal body weight mice. The data support that high-dose leptin has proliferative effect on CD4+ cells in vivo. However, more in vivo study needs to be examined to clarify how leptin affect lymphocyte subpopulations.

Efficient Expression of Bioactive Human Leptin in Escherichia coli in Soluble Fusion Form

Leptin, a 16 kDa nonglycosylated hormone, is produced by mature adipocytes and functions primarily in the hypothalamus to reduce food intake and body weight. To explore a new approach for high-level expression of human Leptin in Escherichia coli, the human Leptin gene, synthesized according to the published sequence, was cloned into the vector pET32a to construct a fusion expression plasmid: Trx-Leptin/pET32a. Our data showed that more than 40% of the fusion protein Trx-Leptin was expressed in soluble form. After purified by Ni-IDA affinity chromatography, cleaved by enterokinase and applied Ni-IDA affinity chromatography again, purified Leptin with homogeneity over 96% was achieved. The bio-functional experiments of purified Leptin showed a significant reduction in food intake and body weight of female mice treated with Leptin by comparing with control mice, and it indicated that the purified Leptin has full biological activity. In addition, our expression system was a very low-cost and efficient prokaryotic expression system. So taken together, our results demonstrated that our expression system of bio-active Leptin provided a new method for producing Leptin in big scale and would be widely applied in commercial Leptin producing industries.

Structural and functional studies of leptins from hibernating and non-hibernating bats

Leptin, a 16-kDa hormone produced by mature adipocytes, has been shown to regulate the hibernation of mammals. In this study, the leptin gene sequences of both hibernating (Rhinolophus ferrumequinum) and non-hibernating (Rousettus leschenaultii) bats were determined, and the leptin proteins from these two different species of bats were expressed in Escherichia coli for the first time. Results showed that the amino acid sequence of the leptin protein from hibernating bats had a lower degree of identity than that from non-hibernating bats to those of several non-hibernating mammals. The leptin protein of hibernating bats had a stronger growth inhibitory effect on 3T3-L1 cells than that of non-hibernating bats. Structural modeling revealed that the structures of the receptor binding site III, which is critical for signal transduction, of the two bat leptins were very different. Similar to the human leptin, the leptin protein of non-hibernating bats was predicted to have a random loop, whereas that of hibernating bats had a helical structure in this region. This observation provided a clue as to the differential effects of the two different leptins on 3T3-L1 cells.

Gene structure, recombinant expression and functional characterization of grass carp leptin

Leptin is an important hormone for the regulation of food intake, energy expenditure and reproduction in mammals, but information regarding its role in teleosts remains scant. In the present study, the gene structures of grass carp (Ctenopharyngodon idellus) and silver carp (Hypophthalmichthys molitrix) leptins were characterized. Recombinant grass carp leptin (rgc-LEP) was expressed in Escherichia coli and purified, and identified by mass spectrometric analysis. A strong anorexic effect on food intake was observed in grass carp on the first day after intraperitoneal (IP) injection of rgc-LEP, but not during the following days. Body weight of the leptin group (LEP group) and the pair-fed group (PF group) showed no difference throughout the experimental period. The acute and chronic effects on the expression of key genes correlating to food intake, energy expenditure, lipid metabolism and digestion were further characterized by real-time PCR. Accordingly, the mRNA levels of neuropeptide Y (NPY), Stearoyl-CoA desaturase 1 (SCD1) and lipoprotein lipase (LPL) were significantly reduced whereas the mRNA levels of uncoupling protein 2 (UCP2), bile salt-activated lipase (BSAL) and fatty acid elongase (ELO) were significantly elevated on the first day after injection. No effect on the expression of these genes (except LPL) was observed on day 13. In contrast to the down-regulation by exogenous leptin in mammals, the mRNA level of grass carp leptin was elevated 5.76-fold on the first day after rgc-LEP treatment. Our results suggest that leptin has an acute effect on the regulation of food intake, energy expenditure and lipid metabolism in grass carp, but the effect can be rapidly counteracted through mechanisms that are currently unknown.

Purification and characterization of recombinant pufferfish (Takifugu rubripes) leptin

Synthetic cDNA encoding pufferfish (Takifugu rubripes) leptin (pfLEP) was prepared according to the published sequence. The pfLEP, transformed into Escherichia coli and expressed upon induction with nalidixic acid, was found almost entirely in the insoluble inclusion bodies (IBs). The proteins were solubilized, refolded and purified to homogeneity by anion-exchange chromatography and gel-filtration. The respective yield of dimers and monomers was 50-100mg from 5L of fermentation culture. Circular dichroism analyses revealed similarity of the purified pfLEP secondary structure to that of mammalian leptins. The purified monomers and dimers showed a single band of approximately 15 kDa following SDS-PAGE in the presence of reducing agent, whereas the dimer showed one band of approximately 30 kDa in the absence of reducing agent, indicating its formation by S-S bonds. The purified product also showed a single peak following gel-filtration under nondenaturating conditions and reverse-phase chromatography. Monomeric and dimeric pfLEPs were stable for at least 6 months in sterile solution frozen at -20 degrees C or as lyophilized powder. Both pfLEPs were biologically active in promoting proliferation of BAF/3 cells stably transfected with the long form of human leptin (hLEP) receptor, but their activity was four to five orders of magnitude lower than that of hLEP. The specificity of this activity was further evidenced by its complete inhibition by hLEP antagonist. In contrast to mammalian leptins, neither form of pfLEP bound to or formed 1:1 complex with chicken leptin-binding domain, likely due to low affinity. No specific binding of either ovine or pufferfish leptins to tilapia liver membranes was detected. This work is the first report on the purification of leptin from any fish species.

Leptin levels and body composition of mice selectively bred for high voluntary locomotor activity

Selective breeding produced four replicate lines of high-runner (HR) mice that run on wheels for approximately 2.7 times more revolutions per day than four unselected control lines. Previous studies found that HR mice of both sexes have lower body fat (isotope dilution at 15 wk of age) and that males (females not studied) have smaller retroperitoneal fat pads (17 wk). HR mice also exhibit elevated plasma corticosterone and insulin-stimulated glucose uptake by some hindlimb muscles but apparently do not differ in circulating insulin or glucose levels (males at 18 wk). Given their lower body fat and higher activity levels, we hypothesized that HR mice would have lower circulating leptin levels than controls. Female mice were given wheel access for 6 d at 7 wk of age, as part of the routine wheel testing for the selective breeding protocol, and then were killed after one additional week without wheels to reduce possible acute effects of activity on leptin. As hypothesized, serum leptin levels were significantly lower in HR mice. ANCOVA indicated that leptin was strongly positively correlated with both total body fat (measured by ether extraction) and body mass change from weaning, but HR mice still had significantly lower adjusted leptin levels (ANCOVA). Within HR lines but not within control lines, individual variation in leptin levels was negatively correlated with amount or speed of wheel running measured a week before being killed. Growth from weaning to euthanasia and body dry mass were lower in HR mice than in controls, but absolute dry masses of the ventricles, liver, gut, and uterus plus ovaries did not significantly differ, nor did percentage of the total dry mass as fat. HR mice offer a novel model for studying the causes and consequences of physiologically relevant variations in serum leptin.

Leptin receptor isoform expression in rat osteoblasts and their functional analysis

The genetic defect in producing the adipose hormone leptin results among others in a drastic increase of bone mass. The current understanding is that under normal circumstances, osteoblast activity is indirectly suppressed by a hypothalamic relay induced by leptin-signalling in the brain. To investigate whether leptin might also regulate osteoblast activity in a direct manner, expression of leptin receptors in rat osteoblasts was determined and their functionality was analyzed upon recombinant leptin treatment. Reverse transcription-PCR confirmed the expression of four among the six currently described receptor isoforms, which were also able to transduce cell signalling as shown by STAT3 phosphorylation after activation.