Colipase: structure and interaction with pancreatic lipase

Methodologies for Assessing Pancreatic Lipase Catalytic Activity: A Review

Obesity is a disease of epidemic proportions with a concerning increasing trend. Regarded as one of the main sources of energy, lipids can also represent a big part of an unnecessary intake of calories and be, therefore, directly related to the problem of obesity. Pancreatic lipase is an enzyme that is essential in the absorption and digestion of dietary fats and has been explored as an alternative for the reduction of fat absorption and consequent weigh loss.Literature describes a great variability of methodologies and experimental conditions used in research to evaluate the in vitro inhibitory activity of compounds against pancreatic lipase. However, in an attempt to choose the best approach, it is necessary to know all the reaction conditions and understand how these can affect the enzymatic assay.The objective of this review is to understand and summarize the methodologies and respective experimental conditions that are mainly used to evaluate pancreatic lipase catalytic activity.156 studies were included in this work and a detailed description of the most commonly used UV/Vis spectrophotometric and fluorimetric instrumental techniques are presented, including a discussion regarding the differences found in the parameters used in both techniques, namely enzyme, substrate, buffer solutions, kinetics conditions, temperature and pH.This works shows that both UV/Vis spectrophotometry and fluorimetry are useful instrumental techniques for the evaluation of pancreatic lipase catalytic activity, presenting several advantages and limitations, which make the choice of parameters and experimental conditions a crucial decision to obtain the most reliable results.

Comparative Transcriptomics and Methylomics Reveal Adaptive Responses of Digestive and Metabolic Genes to Dietary Shift in Giant and Red Pandas

Both the giant panda (Ailuropoda melanoleuca) and red panda (Ailurus fulgens) belong to the order Carnivora, but have changed their dietary habits to eating bamboo exclusively. The convergent evolution characteristics of their morphology, genome and gut flora have been found in the two pandas. However, the research on the convergent adaptation of their digestion and metabolism to the bamboo diet, mediated by the dietary shift of the two pandas at the gene-expression and epigenetic regulation levels, is still lacking. We therefore used RNA sequencing among five species (two pandas and three non-herbivore mammals) and bisulfite sequencing among three species (two pandas and a carnivore ferret) to sequence key digestion and metabolism tissues (stomach and small intestine). Our results provide evidence that the convergent differentially expressed genes (related to carbohydrate utilization, bile secretion, Lys and Arg metabolism, vitamin B12 utilization and cyanide detoxification) of the two pandas are adaptive responses to the bamboo diet containing low lipids, low Lys and Arg, low vitamin B12 and high cyanide. We also profiled the genome-wide methylome maps of giant panda, red panda and ferret, and the results indicated that the promoter methylation of the two pandas may regulate digestive and metabolic genes to adapt to sudden environmental changes, and then, transmit genetic information to future generations to evolve into bamboo eaters. Taken together, our study provides new insights into the molecular mechanisms of the dietary shift and the adaptation to a strict bamboo diet in both pandas using comparative transcriptomics and methylomics.

Identification of cell-type-specific spatially variable genes accounting for excess zeros

MOTIVATION

Spatial transcriptomic techniques can profile gene expressions while retaining the spatial information, thus offering unprecedented opportunities to explore the relationship between gene expression and spatial locations. The spatial relationship may vary across cell types, but there is a lack of statistical methods to identify cell-type-specific spatially variable (SV) genes by simultaneously modeling excess zeros and cell-type proportions.

RESULTS

We develop a statistical approach CTSV to detect cell-type-specific SV genes. CTSV directly models spatial raw count data and considers zero-inflation as well as overdispersion using a zero-inflated negative binomial distribution. It then incorporates cell-type proportions and spatial effect functions in the zero-inflated negative binomial regression framework. The R package pscl is employed to fit the model. For robustness, a Cauchy combination rule is applied to integrate P-values from multiple choices of spatial effect functions. Simulation studies show that CTSV not only outperforms competing methods at the aggregated level but also achieves more power at the cell-type level. By analyzing pancreatic ductal adenocarcinoma spatial transcriptomic data, SV genes identified by CTSV reveal biological insights at the cell-type level.

AVAILABILITY AND IMPLEMENTATION

The R package of CTSV is available at https://bioconductor.org/packages/devel/bioc/html/CTSV.html.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Repurposing of the approved small molecule drugs in order to inhibit SARS-CoV-2 S protein and human ACE2 interaction through virtual screening approaches

Most recently, the new coronavirus (SARS-CoV-2) has been recognized as a pandemic by the World Health Organization (WHO) while this virus shares substantial similarity with SARS-CoV. So far, no definitive vaccine or drug has been developed to cure Covid-19 disease, since many important aspects about Covid-19 such as pathogenesis and proliferation pathways are still unclear. It was proven that human ACE2 is the main receptor for the entry of Covid-19 into lower respiratory tract epithelial cells through interaction with SARS-CoV-2 S protein. Based on this observation, it is expected that the virus infection can be inhibited if protein-protein interaction is prevented. In this study, using structure-based virtual screening of FDA databases, several lead drugs were discovered based on the ACE2-binding pocket of SARS-CoV-2 S protein. Then, binding affinity, binding modes, critical interactions, and pharmaceutical properties of the lead drugs were evaluated. Among the previously approved drugs, Diammonium Glycyrrhizinate, Digitoxin, Ivermectin, Rapamycin, Rifaximin, and Amphotericin B represented the most desirable features, and can be possible candidates for Covid-19 therapies. Furthermore, molecular dynamics (MD) simulation was accomplished for three S protein/drug complexes with the highest binding affinity and best conformation and binding free energies were also computed with the Molecular Mechanics/Poisson-Boltzmann Surface Area (MM/PBSA) method. Results demonstrated the stable binding of these compounds to the S protein; however, in order to confirm the curative effect of these drugs, clinical trials must be done.

Prokineticin-Receptor Network: Mechanisms of Regulation

Prokineticins are a new class of chemokine-like peptides that bind their G protein-coupled receptors, PKR1 and PKR2, and promote chemotaxis and the production of pro-inflammatory cytokines following tissue injury or infection. This review summarizes the major cellular and biochemical mechanisms of prokineticins pathway regulation that, like other chemokines, include: genetic polymorphisms; mRNA splice modulation; expression regulation at transcriptional and post-transcriptional levels; prokineticins interactions with cell-surface glycosaminoglycans; PKRs degradation, localization, post-translational modifications and oligomerization; alternative signaling responses; binding to pharmacological inhibitors. Understanding these mechanisms, which together exert substantial biochemical control and greatly enhance the complexity of the prokineticin-receptor network, leads to novel opportunities for therapeutic intervention. In this way, besides targeting prokineticins or their receptors directly, it could be possible to indirectly influence their activity by modulating their expression and localization or blocking the downstream signaling pathways.

Dietary fatty acids in gut health: Absorption, metabolism and function

In biological responses, fatty acids (FA) are absorbed and metabolized in the form of substrates for energy production. The molecular structures (number of double bonds and chain length) and composition of dietary FA impact digestion, absorption and metabolism, and the biological roles of FA. Recently, increasing evidence indicates that FA are essentially utilized as an energy source and are signaling molecules that exert physiological activity of gut microbiota and immune responses. In addition, FA could serve as natural ligands for orphan G protein-coupled receptors (GPCR), also called free fatty acid receptors (FFAR), which intertwine metabolic and immune systems via multiple mechanisms. The present review explores the recent findings on FA absorption and its impact on gut health, particularly addressing the mechanism by which dietary FA potentially influences intestinal microbiota and epithelial functions. Also, this work attempts to uncover research ideas for devising future strategies for manipulating the composition of dietary FA to regulate gut health and support a normal immune system for metabolic and immune disorders.

Enzymes to unravel bioproducts architecture

Enzymes are essential and ubiquitous biocatalysts involved in various metabolic pathways and used in many industrial processes. Here, we reframe enzymes not just as biocatalysts transforming bioproducts but also as sensitive probes for exploring the structure and composition of complex bioproducts, like meat tissue, dairy products and plant materials, in both food and non-food bioprocesses. This review details the global strategy and presents the most recent investigations to prepare and use enzymes as relevant probes, with a focus on glycoside-hydrolases involved in plant deconstruction and proteases and lipases involved in food digestion. First, to expand the enzyme repertoire to fit bioproduct complexity, novel enzymes are mined from biodiversity and can be artificially engineered. Enzymes are further characterized by exploring sequence/structure/dynamics/function relationships together with the environmental factors influencing enzyme interactions with their substrates. Then, the most advanced experimental and theoretical approaches developed for exploring bioproducts at various scales (from nanometer to millimeter) using active and inactive enzymes as probes are illustrated. Overall, combining multimodal and multiscale approaches brings a better understanding of native-form or transformed bioproduct architecture and composition, and paves the way to mainstream the use of enzymes as probes.

Colloidal aspects of digestion of Pickering emulsions: Experiments and theoretical models of lipid digestion kinetics

Lipid digestion is a bio-interfacial process that is largely governed by the binding of the lipase-colipase-biosurfactant (bile salts) complex onto the surface of emulsified lipid droplets. Therefore, engineering oil-water interfaces that prevent competitive displacement by bile salts and/or delay the transportation of lipase to the lipidoidal substrate can be an effective strategy to modulate lipolysis in human physiology. In this review, we present the mechanistic role of Pickering emulsions i.e. emulsions stabilised by micron-to-nano sized particles in modulating the important fundamental biological process of lipid digestion by virtue of their distinctive stability against coalescence and resilience to desorption by intestinal biosurfactants. We provide a systematic summary of recent experimental investigations and mathematical models that have blossomed in the last decade in this domain. A strategic examination of the behavior and mechanism of lipid digestion of droplets stabilised by particles in simulated biophysical environments (oral, gastric, intestinal regimes) was conducted. Various particle-laden interfaces were considered, where the particles were derived from synthetic or biological sources. This allowed us to categorize these particles into two classes based on their mechanistic role in modifying lipid digestion. These are 'human enzyme-unresponsive particles' (e.g. silica, cellulose, chitin, flavonoids) i.e. the ones that cannot to be digested by human enzymes, such as amylase, protease and 'human enzyme-responsive particles' (e.g. protein microgels, starch granules), which can be readily digested by humans. We focused on the role of particle shape (spherical, anisotropic) on modifying both interfacial and bulk phases during lipolysis. Also, the techniques currently used to alter the kinetics of lipid digestion using intelligent physical or chemical treatments to control interfacial particle spacing were critically reviewed. A comparison of how various mathematical models reported in literature predict free fatty acid release kinetics during lipid digestion highlighted the importance of the clear statement of the underlying assumptions. We provide details of the initial first order kinetic models to the more recent models, which account for the rate of adsorption of lipase at the droplet surface and include the crucial aspect of interfacial dynamics. We provide a unique decision tree on model selection, which is appropriate to minimize the difference between experimental data of free fatty acid generation and model predictions based on precise assumptions of droplet shrinkage, lipase-binding rate, and nature of lipase transport process to the particle-laden interface. Greater insights into the mechanisms of controlling lipolysis using particle-laden interfaces with appropriate mathematical model fitting permit better understanding of the key lipid digestion processes. Future outlook on interfacial design parameters, such as particle shape, size, polydispersity, charge, fusion, material chemistry, loading and development of new mathematical models that provide closed-loop equations from early to later stages of kinetics are proposed. Such future experiments and models hold promise for the tailoring of particle-laden interfaces for delaying lipid digestion and/or site-dependent controlled release of lipidic active molecules in composite soft matter systems, such as food, personal care, pharmaceutical, healthcare and biotechnological applications.

Red drum Sciaenops ocellatus growth and expression of bile salt-dependent lipase in response to increasing dietary lipid supplementation

Sciaenops ocellatus has a long history in aquaculture and many difficulties associated with its commercial culture have been addressed and successfully resolved; nevertheless, further research in lipid nutrition could address more comprehensive questions on the way these nutrients are utilized. The purpose of this study was to evaluate S. ocellatus growth and lipase gene expression in response to increasing dietary lipid supplementation. Four experimental diets were formulated to provide 3, 10, 16, or 23% lipid using menhaden fish oil. Twenty juveniles (mean initial weight 2.3 ± 0.1 g) were stocked per aquaria in a recirculating system; each diet was assigned to three aquaria and fed to fish for 6 weeks. At the end of the study, fish fed 3% of dietary lipid were significantly (P < 0.0001) smaller and showed significantly lower feed efficiency, condition factor, hepatosomatic index, and intraperitoneal fat than fish fed the other diets, but no differences were observed among fish fed 10, 16, or 23% lipid. A straight broken-line regression model for thermal growth coefficient provided an estimated value of 9.4% of dietary lipid as the optimal inclusion level. The bile salt-dependent lipase (BSDL) of red drum was 80.3 kDa. Relative gene expression of BSDL was significantly higher (P = 0.0007) in fish fed 10% lipid, with no differences among the other dietary treatments. Results provided could help monitor the metabolic status of farmed fish and contribute to optimize diet formulations based on maximum gene expression of BSDL for supplementation of dietary lipid.

Polyphenolic Compounds and Digestive Enzymes: In Vitro Non-Covalent Interactions

The digestive enzymes–polyphenolic compounds (PCs) interactions behind the inhibition of these enzymes have not been completely studied. The existing studies have mainly analyzed polyphenolic extracts and reported inhibition percentages of catalytic activities determined by UV-Vis spectroscopy techniques. Recently, pure PCs and new methods such as isothermal titration calorimetry and circular dichroism have been applied to describe these interactions. The present review focuses on PCs structural characteristics behind the inhibition of digestive enzymes, and progress of the used methods. Some characteristics such as molecular weight, number and position of substitution, and glycosylation of flavonoids seem to be related to the inhibitory effect of PCs; also, this effect seems to be different for carbohydrate-hydrolyzing enzymes and proteases. The digestive enzyme–PCs molecular interactions have shown that non-covalent binding, mostly by van der Waals forces, hydrogen binding, hydrophobic binding, and other electrostatic forces regulate them. These interactions were mainly associated to non-competitive type inhibitions of the enzymatic activities. The present review emphasizes on the digestive enzymes such as α-glycosidase (AG), α-amylase (PA), lipase (PL), pepsin (PE), trypsin (TP), and chymotrypsin (CT). Existing studies conducted in vitro allow one to elucidate the characteristics of the structure–function relationships, where differences between the structures of PCs might be the reason for different in vivo effects.

The β5-Loop and Lid Domain Contribute to the Substrate Specificity of Pancreatic Lipase-related Protein 2 (PNLIPRP2)

Pancreatic triglyceride lipase (PNLIP) is essential for dietary fat digestion in children and adults, whereas a homolog, pancreatic lipase-related protein 2 (PNLIPRP2), is critical in newborns. The two lipases are structurally similar, yet they have different substrate specificities. PNLIP only cleaves neutral fats. PNLIPRP2 cleaves neutral and polar fats. To test the hypothesis that the differences in activity between PNLIP and PNLIPRP2 are governed by surface loops around the active site, we created multiple chimeras of both lipases by exchanging the surface loops singly or in combination. The chimeras were expressed, purified, and tested for activity against various substrates. The structural determinants of PNLIPRP2 galactolipase activity were contained in the N-terminal domain. Of the surface loops tested, the lid domain and the β5-loop influenced activity against triglycerides and galactolipids. Any chimera on PNLIP with the PNLIPRP2 lid domain or β5-loop had decreased triglyceride lipase activity similar to that of PNLIPRP2. The corresponding chimeras of PNLIPRP2 did not increase activity against neutral lipids. Galactolipase activity was abolished by the PNLIP β5-loop and decreased by the PNLIP lid domain. The source of the β9-loop had minimal effect on activity. We conclude that the lid domain and β5-loop contribute to substrate specificity but do not completely account for the differing activities of PNLIP and PNLIPRP2. Other regions in the N-terminal domain must contribute to the galactolipase activity of PNLIPRP2 through direct interactions with the substrate or by altering the conformation of the residues surrounding the hydrophilic cavity in PNLIPRP2.

Role of the gut in modulating lipoprotein metabolism

The intestinal production of lipoproteins is one of the key processes by which the body prepares dietary lipid for dissemination to locations throughout the body where they are required. Paramount to this is the relationship between dietary lipid and the enterocytes that line the gut, along with the processes which prepare this lipid for efficient uptake by these cells. These include those which occur in the mouth and stomach along with those which occur within the intestinal lumen itself. Additionally, the interplay between digested lipid, dual avenues for lipid uptake by enterocytes (passive and lipid transporter proteins), a system of intercellular lipid resynthesis and transport, and a complex system of lipoprotein synthesis yield a system open to significant modulation. In this review, we will attempt to outline the processes of lipid digestion, lipoprotein synthesis and the exogenous and endogenous factors which exert their influence.

An Isozyme of Earthworm Serine Proteases Acts on Hydrolysis of Triacylglycerol

An enzyme catalyzing the hydrolysis of triacylglycerol was purified from an earthworm. The N-terminal amino acid sequence and the catalytic function of the purified enzyme were identical to those of Isozyme C, an isozyme of the earthworm-serine proteases. No other lipase proteins were found in the earthworm cells. The isozyme might act on the hydrolysis of triacylglycerol as well as the protein decomposition.

Hepatic lipase is expressed by osteoblasts and modulates bone remodeling in obesity

A number of unexpected molecules were recently identified as products of osteoblasts, linking bone homeostasis to systemic energy metabolism. Here we identify the lipolytic enzyme hepatic lipase (HL, encoded by Lipc) as a novel cell-autonomous regulator of osteoblast function. In an unbiased genome-wide expression analysis, we find Lipc to be highly induced upon osteoblast differentiation, verified by quantitative Taqman analyses of primary osteoblasts in vitro and of bone samples in vivo. Functionally, loss of HL in vitro leads to increased expression and secretion of osteoprotegerin (OPG), while expression of some osteoblast differentiation makers is impaired. When challenging energy metabolism in a diet-induced obesity (DIO) study, lack of HL leads to a significant increase in bone formation markers and a decrease in bone resorption markers. Accordingly, in the DIO setting, we observe in Lipc(-/-) animals but not in wild-type controls a significant increase in lumbar vertebral trabecular bone mass and formation rate as well as in femoral trabecular bone mass and cortical thickness. Taken together, we demonstrate that HL expressed by osteoblasts has an impact on osteoblast OPG expression and that lack of HL leads to increased bone mass in DIO. These data provide a novel and completely unexpected molecular link in the complex interplay of osteoblasts and systemic energy metabolism.

High expression of the secreted protein dickkopf homolog 4: roles in invasion and metastasis of renal cell carcinoma and its association with Von Hippel-Lindau gene

The aim of this study was to investigate the effects of the dickkopf homolog 4 (DKK4)/Wnt/β-catenin signaling pathway on tumorigenesis and metastasis in clear cell renal cell carcinoma (ccRCC), as well as to elucidate the underlying mechanisms. We examined the expression of DKK4 in 30 cases of ccRCC and matched adjacent normal tissues, and investigated its correlation with clinicopathological characteristics. Stable DKK4-transfected cells were established, and DKK4 functional analyses were performed, including a T-cell factor/lymphoid enhancer factor (TCF/LEF) reporter assay, and experiments on cell viability, apoptosis, invasive capability and tumor growth in vivo. Finally, western blot analysis was performed to detect Von Hippel-Lindau (VHL) expression in 50 clinical specimens. The expression levels of the DKK4, β-catenin and β-catenin downstream target genes, cyclin D1 and c-myc, were determined in the these specimens, as well as in RCC4(-), T3-14(+) cell lines by qRT-PCR and western blot analysis. The same tests were also performed in human embryonic kidney (HEK)293 cells which were transfected with the pCDH-DKK4 plasmid. After 6 weeks the tumor weight significantly increased in the mice transfected with the tumor cells. DKK4 mRNA and protein expression levels were significantly upregulated (p<0.001). DKK4 was distinctly overexpressed (68.0%) in all patient tissues. VHL(-) samples accounted for 60.0% of all samples, while DKK4 expression was significantly upregulated in 50% of these samples, indicating a correlation with VHL(-) expression (r=0.403, p<0.05). We also observed reduced expression levels of cyclin D1, c-myc and β-catenin (to a greater extent) in the VHL(-), RCC4(-) and T3-14(+) cells, as well as in the stably transfected HEK293 cells. DKK4 may be an oncogene, and its upregulated expression may be involved in the pathogenesis of ccRCC as a downstream gene of VHL. By activating other pathways apart from the Wnt/β-catenin pathway, DKK4 may play an important role in ccRCC tumorigenesis and metastasis.

Identification of a novel mutation in the PNLIP gene in two brothers with congenital pancreatic lipase deficiency

Congenital pancreatic lipase (PNLIP) deficiency is a rare monoenzymatic form of exocrine pancreatic failure characterized by decreased absorption of dietary fat and greasy voluminous stools, but apparent normal development and an overall good state of health. While considered to be an autosomal recessive state affecting a few dozens of individuals world-wide and involving the PNLIP gene, no causative mutations for this phenotype were so far reported. Here, we report the identification of the homozygote missense mutation, Thr221Met [c.662C>T], in two brothers from a consanguineous family of Arab ancestry. The observed genotypes among the family members were concordant with an autosomal recessive mode of inheritance but moreover a clear segregation between the genotype state and the serum PNLIP activity was evident. Based on biophysical computational tools, we suggest the mutation disrupts the protein's stability and impairs its normal function. Although the role of PNLIP is well established, our observations provide genetic evidence that PNLIP mutations are causative for this phenotype.

Integration of metabolomics and transcriptomics revealed a fatty acid network exerting growth inhibitory effects in human pancreatic cancer

PURPOSE

To identify metabolic pathways that are perturbed in pancreatic ductal adenocarcinoma (PDAC), we investigated gene-metabolite networks with integration of metabolomics and transcriptomics.

EXPERIMENTAL DESIGN

We conducted global metabolite profiling analysis on two independent cohorts of resected PDAC cases to identify critical metabolites alteration that may contribute to the progression of pancreatic cancer. We then searched for gene surrogates that were significantly correlated with the key metabolites, by integrating metabolite and gene expression profiles.

RESULTS

Fifty-five metabolites were consistently altered in tumors as compared with adjacent nontumor tissues in a test cohort (N = 33) and an independent validation cohort (N = 31). Weighted network analysis revealed a unique set of free fatty acids (FFA) that were highly coregulated and decreased in PDAC. Pathway analysis of 157 differentially expressed gene surrogates revealed a significantly altered lipid metabolism network, including key lipolytic enzymes PNLIP, CLPS, PNLIPRP1, and PNLIPRP2. Gene expressions of these lipases were significantly decreased in pancreatic tumors as compared with nontumor tissues, leading to reduced FFAs. More importantly, a lower gene expression of PNLIP in tumors was associated with poorer survival in two independent cohorts. We further showed that two saturated FFAs, palmitate and stearate, significantly induced TRAIL expression, triggered apoptosis, and inhibited proliferation in pancreatic cancer cells.

CONCLUSIONS

Our results suggest that impairment in a lipolytic pathway involving lipases, and a unique set of FFAs, may play an important role in the development and progression of pancreatic cancer and provide potential targets for therapeutic intervention.

The Arg92Cys colipase polymorphism impairs function and secretion by increasing protein misfolding

Colipase is essential for efficient fat digestion. An arginine-to-cysteine polymorphism at position 92 of colipase (Arg92Cys) associates with an increased risk for developing type-2 diabetes through an undefined mechanism. To test our hypothesis that the extra cysteine increases colipase misfolding, thereby altering its intracellular trafficking and function, we expressed Cys92 colipase in HEK293T cells. Less Cys92 colipase is secreted and more is retained intracellularly in an insoluble form compared with Arg92 colipase. Nonreducing gel electrophoresis suggests the folding of secreted Cys92 colipase differs from Arg92 colipase. Cys92 colipase misfolding does not trigger the unfolded protein response (UPR) or endoplasmic reticulum (ER) stress. The ability of secreted Cys92 colipase to stimulate pancreatic triglyceride lipase (PTL) is reduced with all substrates tested, particularly long-chain triglycerides. The reaction of Cys92 colipase with triolein and Intralipid has a much longer lag time, reflecting decreased ability to anchor PTL on those substrates. Our data predicts that humans with the Arg92Cys substitution will secrete less functional colipase into the duodenum and have less efficient fat digestion. Whether inefficient fat digestion or another property of colipase contributes to the risk for developing diabetes remains to be clarified.

Dickkopfs and Wnt/β-catenin signalling in liver cancer

Liver cancer is the fifth and seventh most common cause of cancer in men and women, respectively. Wnt/β-catenin signalling has emerged as a critical player in both the development of normal liver as well as an oncogenic driver in hepatocellular carcinoma (HCC). Based on the current understanding, this article summarizes the possible mechanisms for the aberrant activation of this pathway with specific focus on HCC. Furthermore, we will discuss the role of dickkopfs (DKKs) in regulating Wnt/β-catenin signalling, which is poorly understood and understudied. DKKs are a family of secreted proteins that comprise at least four members, namely DKK1-DKK4, which act as inhibitors of Wnt/β-catenin signalling. Nevertheless, not all members antagonize Wnt/β-catenin signalling. Their functional significance in hepatocarcinogenesis remains to be further characterized for which these studies should provide new insights into the regulatory role of DKKs in Wnt/β-catenin signalling in hepatic carcinogenesis. Because of the important oncogenic roles, there are an increasing number of therapeutic molecules targeting β-catenin and the Wnt/β-catenin pathway for potential therapy of HCC.

Pancreatic lipase-related protein-2 (PLRP2) can contribute to dietary fat digestion in human newborns

In newborn mice, PLRP2 is essential for fat digestion. In human infants, the role of PLRP2 in fat digestion is unclear, as it has poor activity against long-chain triglycerides in vitro. Also, many infants carry a genetic polymorphism resulting in a truncated protein, PLRP2 W340X, which may impact function significantly. We re-examined the properties of recombinant human PLRP2 and studied the impact of W340X mutation on its function. In the presence of bile salt micelles and colipase, human PLRP2 hydrolyzed long-chain tri-, di-, and monoglycerides. It hydrolyzed triolein at a level much lower than that of pancreatic triglyceride lipase, but close to that of carboxyl ester lipase, after a long lag phase, which could be eliminated by the addition of oleic acids. Human PLRP2 W340X was poorly secreted and largely retained inside the cell. The retention of the mutant protein triggered endoplasmic reticulum stress and unfolded protein responses. Our results show that earlier studies underestimated human PLRP2 activity against triolein by employing suboptimal assay conditions. In vivo, dietary fat emulsions contain fatty acids as a result of the action of gastric lipase. Consequently, PLRP2 can contribute to fat digestion during early infancy. Furthermore, infants with homozygous W340X alleles will not secrete functional PLRP2 and may have inefficient dietary fat digestion, particularly when breastfeeding is unavailable. Additionally, the aberrant folding of W340X mutant may cause chronic cellular stress and increase susceptibility of pancreatic exocrine cells to other metabolic stressors.

Injectable hydrogel scaffold from decellularized human lipoaspirate

Soft tissue fillers are rapidly gaining popularity for aesthetic improvements or repair of adipose tissue deficits. Several injectable biopolymers have been investigated for this purpose, but often show rapid resorption or limited adipogenesis and do not mimic the native adipose extracellular matrix (ECM). We have generated an injectable adipose matrix scaffold by efficiently removing both the cellular and lipid contents of human lipoaspirate. The decellularized material retained the complex composition of peptides and glycosaminoglycans found in native adipose ECM. This matrix can be further processed by solubilizing the extracted ECM to generate a thermally responsive hydrogel that self-assembles upon subcutaneous injection. This hydrogel also supports the growth and survival of patient matched adipose-derived stem cells in vitro. The development of an injectable hydrogel from human lipoaspirate represents a minimally invasive option for adipose tissue engineering in terms of both the collection of source material and delivery of the scaffold.

Generation and selection of novel fully human monoclonal antibodies that neutralize Dickkopf-1 (DKK1) inhibitory function in vitro and increase bone mass in vivo

Wnt/LRP5 signaling is a central regulatory component of bone formative and resorptive activities, and the pathway inhibitor DKK1 is a suppressor of bone formation and bone mass accrual in mice. In addition, augmented DKK1 levels are associated with high bone turnover in diverse low bone mass states in rodent models and disease etiologies in human. However, examination of the precise role of DKK1 in the normal skeleton and in higher species requires the development of refined DKK1-specific pharmacological tools. Here, we report the strategy resulting in isolation of a panel of fully human anti-DKK1 antibodies applicable to studies interrogating the roles of mouse, rhesus, and human DKK1. Selected anti-DKK1 antibodies bind primate and human DKK-1 with picomolar affinities yet do not appreciably bind to DKK2 or DKK4. Epitopes mapped within the DKK1 C-terminal domain necessary for interaction with LRP5/6 and consequently effectively neutralized DKK1 function in vitro. When introduced into naïve normal growing female mice, IgGs significantly improved trabecular bone volume and structure and increased both trabecular and cortical bone mineral densities in a dose-related fashion. Furthermore, fully human DKK1-IgG displayed favorable pharmacokinetic parameters in non-human primates. In summary, we demonstrate here a rate-limiting function of physiologic DKK1 levels in the regulation of bone mass in intact female mice, amendable to specific pharmacologic neutralization by newly identified DKK1-IgGs. Importantly the fully human IgGs display a profile of attributes that recommends their testing in higher species and their use in evaluating DKK1 function in relevant disease models.

Regulation of the activity of 5-lipoxygenase, a key enzyme in leukotriene biosynthesis

5-Lipoxygenase (5LO) catalyzes two steps in the biosynthesis of leukotrienes (LTs), lipid mediators of inflammation derived from arachidonic acid. LTs function in normal host defense, and have pathophysiological roles in chronic inflammatory diseases as asthma and atherosclerosis. Also, possible effects of 5LO products in relation to tumorigenesis have been described. Thus, insight regarding the biochemistry of 5LO is relevant for better understanding of normal physiology, and for development of therapy.

Physiological parameters governing the action of pancreatic lipase

The most widely used pharmacological therapies for obesity and weight management are based on inhibition of gastrointestinal lipases, resulting in a reduced energy yield of ingested foods by reducing dietary lipid absorption. Colipase-dependent pancreatic lipase is believed to be the major gastrointestinal enzyme involved in catalysis of lipid ester bonds. There is scant literature on the action of pancreatic lipase under the range of physiological conditions that occur within the human small intestine, and the literature that does exist is often contradictory. Due to the importance of pancreatic lipase activity to nutrition and weight management, the present review aims to assess the current body of knowledge with regards to the physiology behind the action of this unique gastrointestinal enzyme system. Existing data would suggest that pancreatic lipase activity is affected by intestinal pH, the presence of colipase and bile salts, but not by the physiological range of Ca ion concentration (as is commonly assumed). The control of secretion of pancreatic lipase and its associated factors appears to be driven by gastrointestinal luminal content, particularly the presence of acid or digested proteins and fats in the duodenal lumen. Secretion of colipase, bile acids and pancreatic lipase is driven by cholecystokinin and secretin release.

Comparative and functional genomics of lipases in holometabolous insects

Lipases have key roles in insect lipid acquisition, storage and mobilisation and are also fundamental to many physiological processes underpinning insect reproduction, development, defence from pathogens and oxidative stress, and pheromone signalling. We have screened the recently sequenced genomes of five species from four orders of holometabolous insects, the dipterans Drosophila melanogaster and Anopheles gambiae, the hymenopteran Apis mellifera, the moth Bombyx mori and the beetle Tribolium castaneum, for the six major lipase families that are also found in other organisms. The two most numerous families in the insects, the neutral and acid lipases, are also the main families in mammals, albeit not in Caenorhabditis elegans, plants or microbes. Total numbers of the lipases vary two-fold across the five insect species, from numbers similar to those in mammals up to numbers comparable to those seen in C. elegans. Whilst there is a high degree of orthology with mammalian lipases in the other four families, the great majority of the insect neutral and acid lipases have arisen since the insect orders themselves diverged. Intriguingly, about 10% of the insect neutral and acid lipases have lost motifs critical for catalytic function. Examination of the length of lid and loop regions of the neutral lipase sequences suggest that most of the insect lipases lack triacylglycerol (TAG) hydrolysis activity, although the acid lipases all have intact cap domains required for TAG hydrolysis. We have also reviewed the sequence databases and scientific literature for insights into the expression profiles and functions of the insect neutral and acid lipases and the orthologues of the mammalian adipose triglyceride lipase which has a pivotal role in lipid mobilisation. These data suggest that some of the acid and neutral lipase diversity may be due to a requirement for rapid accumulation of dietary lipids. The different roles required of lipases at the four discrete life stages of holometabolous insects may also contribute to the diversity of lipases required by insects. In addition, insects use lipases to perform roles for which there are no correlates in mammals, including as yolk and male accessory gland proteins.

Procolipase gene: no association with early-onset obesity or fat intake

BACKGROUND

Several lines of evidence in volvement of procolipase (CLPS) or its derivative enterostatin in dietary fat absorption, regulation of fat intake, and body weight in rodents. We explored the relationship between genetic variation in CLPS, early-onset obesity and fat intake in humans.

METHODS

We screened the CLPS in 93 extremely obese children and adolescents and 96 underweight young adults for sequence variations and genotyped single nucleotide polymorphisms (SNPs) in extremely obese children and adolescents, healthy normal-and underweight young adults and obesity trios. Case-control and family-based association analyses were performed.

RESULTS

Five sequence variations were identified: two non-synonymous SNPs: rs2766597 (Leu8Pro), rs41270082 (Arg109Cys); one SNP in the 5'UTR: rs3748050; one intronic SNP: rs3748051; and one infrequent novel non-synonymous variant: Arg55His. For rs2766597, rs3748050, and rs3748051 we obtained no evidence for an association with obesity in the case-control comparison. For rs41270082 there was a trend for association which could not be substantiated in the family-based association analysis. Additionally, we found no association in subgroup analyses pertaining to the extremely obese children and adolescents in the lowest and highest quartile of the percentage of energy consumed as fat.

CONCLUSIONS

We found no evidence for an association of CLPS SNPs rs2766597, rs41270082, rs3748050, and rs3748051 with obesity or percentage of dietary fat intake.

Computational study of colipase interaction with lipid droplets and bile salt micelles

Colipase is a key element in the lipase-catalyzed hydrolysis of dietary lipids. Although devoid of enzymatic activity, colipase promotes the pancreatic lipase activity in physiological intestinal conditions by anchoring the enzyme at the surface of lipid droplets. Analysis of structures of NMR colipase models and simulations of their interactions with various lipid aggregates, lipid droplet, and bile salt micelle, were carried out to determine and to map the lipid binding sites on colipase. We show that the micelle and the oil droplet bind to the same side of colipase 3D structure, mainly the hydrophobic fingers. Moreover, it appears that, although colipase has a single direction of interaction with a lipid interface, it does not bind in a specific way but rather oscillates between different positions. Indeed, different NMR models of colipase insert different fragments of sequence in the interface, either simultaneously or independently. This supports the idea that colipase finger plasticity may be crucial to adapt the lipase activity to different lipid aggregates.

Structural insight into the mechanisms of Wnt signaling antagonism by Dkk

Dickkopf (Dkk) proteins are antagonists of the canonical Wnt signaling pathway and are crucial for embryonic cell fate and bone formation. Wnt antagonism of Dkk requires the binding of the C-terminal cysteine-rich domain of Dkk to the Wnt coreceptor, LRP5/6. However, the structural basis of the interaction between Dkk and low density lipoprotein receptor-related protein (LRP) 5/6 is unknown. In this study, we examined the structure of the Dkk functional domain and elucidated its interactions with LRP5/6. Using NMR spectroscopy, we determined the solution structure of the C-terminal cysteine-rich domain of mouse Dkk2 (Dkk2C). Then, guided by mutagenesis studies, we docked Dkk2C to the YWTD beta-propeller domains of LRP5/6 and showed that the ligand binding site of the third LRP5/6 beta-propeller domain matches Dkk2C best, suggesting that this domain binds to Dkk2C with higher affinity. Such differential binding affinity is likely to play an essential role in Dkk function in the canonical Wnt pathway.

Enhancing intestinal drug solubilisation using lipid-based delivery systems

Lipid-based delivery systems are finding increasing application in the oral delivery of poorly water-soluble, lipophilic drugs. Whilst lipidic dose forms may improve oral bioavailability via several mechanisms, enhancement of gastrointestinal solubilisation remains argueably the most important method of absorption enhancement. This review firstly describes the mechanistic rationale which underpins the use of lipid-based delivery systems to enhance drug solubilisation and briefly reviews the available literature describing increases in oral bioavailability after the administration of lipid solution, suspension and self-emulsifying formulations. The use of in vitro methods including dispersion tests and more complex models of in vitro lipolysis as indicators of potential in vivo performance are subsequently described, with particular focus on recent data which suggests that the digestion of surfactants present in lipid-based formulations may impact on formulation performance. Finally, a series of seven guiding principles for formulation design of lipid-based delivery systems are suggested based on an analysis of recent data generated in our laboratories and elsewhere.

A polymorphism in the gene encoding procolipase produces a colipase, Arg92Cys, with decreased function against long-chain triglycerides

Type 2 diabetes mellitus is a multifactorial and polygenic disorder with increasing prevalence. Recently, a polymorphism in the gene encoding procolipase, a cysteine for arginine substitution at position 92, was associated with type 2 diabetes in two human populations. Because procolipase plays a critical role in dietary fat metabolism, polymorphisms that affect the function of procolipase could influence the development of type 2 diabetes. We hypothesized that the Arg92Cys polymorphism has functional consequences. To test our hypothesis, we expressed recombinant cysteine 92 (Cys92) procolipase in a yeast expression system and compared the function and stability of purified Cys92 with that of the more common arginine 92 (Arg92) procolipase. Cys92 fully restored the activity of bile-salt inhibited lipase with short- and medium-chain triglycerides but only had 50% of Arg92 function with long-chain triglycerides. After storage at 4 degrees C, Cys92 lost the ability to restore pancreatic triglyceride lipase activity with medium- and long-chain triglycerides. The loss of function correlated with the inability of Cys92 to anchor lipase on an emulsion surface and oxidation of the cysteine. No detectable degradation or intramolecular disulfide formation occurred in Cys92 after storage. Our findings demonstrate that the Arg92Cys polymorphism decreases the function of Cys92 colipase. This change may contribute to the development of type 2 diabetes.

Molecular imaging of membrane interfaces reveals mode of beta-glucosidase activation by saposin C

Acid beta-glucosidase (GCase) is a soluble lysosomal enzyme responsible for the hydrolysis of glucose from glucosylceramide and requires activation by the small nonenzymatic protein saposin C (sapC) to gain access to the membrane-embedded glycosphingolipid substrate. We have used in situ atomic force microscopy (AFM) with simultaneous confocal and epifluorescence microscopies to investigate the interactions of GCase and sapC with lipid bilayers. GCase binds to sites on membranes transformed by sapC, and enzyme activity occurs at loci containing both GCase and sapC. Using FRET, we establish the presence of GCase/sapC and GCase/product contacts in the bilayer. These data support a mechanism in which sapC locally alters regions of bilayer for subsequent attack by the enzyme in stably bound protein complexes.

Dickkopf-1 regulates gastrulation movements by coordinated modulation of Wnt/beta catenin and Wnt/PCP activities, through interaction with the Dally-like homolog Knypek

Dickkopf-1 (Dkk1) is a secreted protein that negatively modulates the Wnt/beta catenin pathway. Lack of Dkk1 function affects head formation in frog and mice, supporting the idea that Dkk1 acts as a "head inducer" during gastrulation. We show here that lack of Dkk1 function accelerates internalization and rostral progression of the mesendoderm and that gain of function slows down both internalization and convergence extension, indicating a novel role for Dkk1 in modulating these movements. The motility phenotype found in the morphants is not observed in embryos in which the Wnt/beta catenin pathway is overactivated, and that dominant-negative Wnt proteins are not able to rescue the gastrulation movement defect induced by absence of Dkk1. These data strongly suggest that Dkk1 is acting in a beta catenin independent fashion when modulating gastrulation movements. We demonstrate that the glypican 4/6 homolog Knypek (Kny) binds to Dkk1 and that they are able to functionally interact in vivo. Moreover, Dkk1 regulation of gastrulation movements is kny dependent. Kny is a component of the Wnt/planar cell polarity (PCP) pathway. We found that indeed Dkk1 is able to activate this pathway in both Xenopus and zebrafish. Furthermore, concomitant alteration of the beta catenin and PCP activities is able to mimic the morphant accelerated cell motility phenotype. Our data therefore indicate that Dkk1 regulates gastrulation movement through interaction with LRP5/6 and Kny and coordinated modulations of Wnt/beta catenin and Wnt/PCP pathways.

Dickkopf-3 is expressed in a subset of adult human pancreatic beta cells

The Dickkopf (Dkk) gene family of secretory modulators of canonical Wnt/beta catenin signals is involved in the control of stem cell proliferation, homeostasis and differentiation. Bioinformatic data on dkk-1/3 gene expression, indicating high expression levels in the human pancreas, led us to analyze these two proteins in adult human pancreatic tissue. Dkk-1/3 mRNA levels and protein distribution were analyzed in isolated human islets vs. the exocrine/ductal pancreatic cells and in paraffin sections of adult human pancreata. Using real time PCR only lowest amounts of dkk-1 mRNA were detectable in the endocrine fractions. Immunohistochemistry did not reveal any Dkk-1 protein in adult human pancreatic tissue. Interestingly, Dkk-3 mRNA and protein were clearly present in adult human pancreatic islets. Messenger RNA levels for Dkk-3 were significantly higher in isolated islets as compared to the exocrine/ductal fraction. Co-staining with an antibody against insulin identified the beta cells of the pancreas as the Dkk-3-positive cells. Notably, only a subset of beta cells contained Dkk-3. As shown by western blot analysis Dkk-3 seems to be proteolytically processed in beta cells. To our knowledge, this is the first study describing a molecule with which the pool of pancreatic beta cells can be further subdivided. Future studies will show whether this sub-classification of beta cells translates into functional differences.

Structure and function of extracellular phospholipase A1 belonging to the pancreatic lipase gene family

Phospholipase A1 (PLA1) is an enzyme that hydrolyzes phospholipids and produces 2-acyl-lysophospholipids and fatty acids and is conserved in a wide range of organisms. Mammals have several enzymes that exhibit PLA1 activity in vitro. The extracellular PLA1s include phosphatidylserine (PS)-specific PLA1 (PS-PLA1), membrane-associated phosphatidic acid (PA)-selective PLA1s (mPA-PLA1alpha and mPA-PLA1beta), hepatic lipase (HL), endothelial lipase (EL) and pancreatic lipase-related protein 2 (PLRP2), all of which belong to the pancreatic lipase gene family. The former three PLA1s differ from other members in their substrate specificities, structural features and gene organizations, and form a subfamily in the pancreatic lipase gene family. PS-PLA1, mPA-PLA1alpha and mPA-PLA1beta exhibit only PLA1 activity, while HL, EL and PLRP2 show triacylglycerol-hydrolyzing activity in addition to PLA1 activity. The tertiary structures of lipases have two surface loops, the lid and the beta9 loop. The lid and the beta9 loop cover the active site in its closed conformation. An alignment of amino acid sequences of the pancreatic lipase gene family members revealed two molecular characteristics of PLA1s in the two surface loops. First, lipase members exhibiting PLA1 activity (PS-PLA1, mPA-PLA1alpha and mPA-PLA1beta, EL, guinea pig PLRP2 and PLA1 from hornet venom (DolmI)) have short lids. Second, PS-PLA1, mPA-PLA1alpha, mPA-PLA1beta and DolmI, which exhibit only PLA(1) activity, have short beta9 loops. Thus, the two surface loops appear to be involved in the ligand recognition. PS-PLA1 and mPA-PLA1s specifically hydrolyze PS and PA, respectively, producing their corresponding lysophospholipids. Lysophosphatidylserine and lysophosphatidic acid have been defined as lipid mediators with multiple biological functions. Thus, these PLA1s have a role in the production of these lysophospholipid mediators.

Function and biological roles of the Dickkopf family of Wnt modulators

Dickkopf (Dkk) genes comprise an evolutionary conserved small gene family of four members (Dkk1-4) and a unique Dkk3-related gene, Dkkl1 (soggy). They encode secreted proteins that typically antagonize Wnt/beta-catenin signaling, by inhibiting the Wnt coreceptors Lrp5 and 6. Additionally, Dkks are high affinity ligands for the transmembrane proteins Kremen1 and 2, which also modulate Wnt signaling. Dkks play an important role in vertebrate development, where they locally inhibit Wnt regulated processes such as antero-posterior axial patterning, limb development, somitogenesis and eye formation. In the adult, Dkks are implicated in bone formation and bone disease, cancer and Alzheimer's disease.

Coactosin-like protein supports 5-lipoxygenase enzyme activity and up-regulates leukotriene A4 production

Regulation of 5-lipoxygenase (5LO) activity is a key determinant for the biosynthesis of proinflammatory leukotrienes. Coactosin-like protein (CLP) is an F-actin-binding protein that can also bind 5LO. Here, we report that CLP can up-regulate and modulate 5LO activity [formation of 5(S)-hydroperoxy-6-trans-8,11,14-cis-eicosatetraenoic acid (5-HPETE)], 5(S)-hydroxy-6-trans-8,11,14-cis-eicosatetraenoic acid (5-HETE), and 5(S)-trans-5,6-oxido-7,9-trans-11,14-cis-eicosatetraenoic acid (LTA(4)) in vitro. Three findings are presented. First, CLP up-regulates Ca(2+)-induced 5LO activity, in the absence of phosphatidylcholine (membrane). Apparently, CLP can function as a scaffold for 5LO, similar to membranes. Second, CLP gives a considerable (3-fold) increase in the amount of LTA(4) formed by 5LO, when present together with phosphatidylcholine. Third, CLP increases the ratio of 5-HETE/5-HPETE. These effects require protein interaction by Trp residues in ligand-binding loops of the 5LO beta-sandwich; both binding and stimulatory effects of CLP were abolished for the mutant 5LO-W13/75/102A. In polymorphonuclear leukocytes stimulated with Ca(2+) ionophore, both CLP and 5LO associated with the nucleus, whereas in resting cells, CLP and 5LO were cytosolic. These findings establish CLP as a factor relevant for 5LO product formation. Functioning as a 5LO scaffold, CLP may provide a basis for the formation of 5-HETE in the cytosol of different cell types. Furthermore, in stimulated cells, CLP appears to function in a complex together with 5LO and membranes, increasing the capacity of 5LO for leukotriene biosynthesis.

Val-407 and Ile-408 in the beta5'-loop of pancreatic lipase mediate lipase-colipase interactions in the presence of bile salt micelles

In a previous study, we demonstrated that the beta5'-loop in the C-terminal domain of human pancreatic triglyceride lipase (hPTL) makes a major contribution in the function of hPTL (Chahinian et al. (2002) Biochemistry 41, 13725-13735). In the present study, we characterized the contribution of three residues in the beta5'-loop, Val-407, Ile-408, and Leu-412, to the function of hPTL. By substituting charged residues, aspartate or lysine, in these positions, we altered the hydrophilic to lipophilic ratio of the beta5'-loop. Each of the mutants was expressed, purified, and characterized for activity and binding with both monolayers and emulsions and for binding to colipase. Experiments with monolayers and with emulsions suggested that the interaction of hPTL with a phospholipid monolayer differs from the interaction of the hPTL-colipase complex with a dicaprin monolayer or a triglyceride emulsion (i.e. neutral lipids). Val-407, Ile-408, and Leu-412 make major contributions to interactions with monolayers, whereas only Val-407 and Ile-408 appear essential for activity on triglyceride emulsions in the presence of bile salt micelles. In solutions of taurodeoxycholate at micellar concentrations, a major effect of the beta5'-loop mutations is to change the interaction between hPTL and colipase. These observations support a major contribution of residues in the beta5'-loop in the function of hPTL and suggest that a third partner, bile salt micelles or the lipid interface or both, influence the binding of colipase and hPTL through interactions with the beta5'-loop.