Imported: 17 Feb '17 | Published: 23 Sep '14
USPTO - Utility Patents
The present invention concerns Zdhhc2, a new target involved in adipogenesis modulation. Using a siRNA approach, the inventors demonstrated that decrease in Zdhhc2 activity in adipose tissue induces a decrease in adipogenesis. Thus, the present invention relates to modulators of Zdhhc2 activity as well as screening test for identification of modulators of the activity of this target, and their use, especially in pharmaceutical composition, to modulate adipogenesis and thus treat obesity and related disorders.
The present invention concerns Zdhhc2, a new target involved in adipogenesis modulation as well as screening test for identification of modulators of the activity of this target. Further, the present invention relates to modulators of Zdhhc2 activity and their use, especially in pharmaceutical composition, to modulate adipogenesis and thus to treat obesity and related disorders.
Obesity is a major risk factor for a number of disorders including hypertension, coronary artery disease, dyslipidemia, insulin resistance and type 2 diabetes. Because of the importance of the obesity epidemic, a great deal of investigation has centered on the biology of the adipocyte, including the developmental pathway by which new adipocytes are created. Adipogenesis is the process by which undifferentiated mesenchymal precursor cells become mature adipocytes. Throughout the last decade considerable progress has been made in elucidating the molecular mechanisms of adipocyte differentiation, which involve sequential activation of transcription factors from several families such as CCAAT/enhancer binding proteins (C/EBPα, α, and γ) and the nuclear hormone receptor peroxisome proliferator-activated receptor γ (PPARγ) (Rosen, E. D. et al., 2002). PPARγ is described as a “master regulator” of adipogenesis since it has been shown to be both sufficient and necessary for adipogenesis both in vitro and in vivo. Recently, new transcription factors have been described to participate in adipogenesis such as KLF family (KLF2, 5 and KLF15) (Banerjee, S. S. et al., 2003; Gray, S. M. et al., 2002), Ebf family (Jimenez, M. A. et al., 2007) and Krox 20 (Chen, Z. et al., 2005), suggesting that the transcriptional cascade occurring during adipogenesis is much more complex than previously thought. Furthermore, signaling molecules and/or receptors such as the Wnt family of secreted proteins (Kang S. et al., 2007), sonic hedgehog protein, Notch receptor have also been described to be involved in molecular events leading to adipocyte formation.
These last years, an emerging concept has linked the molecular events leading to adipocyte development to the extracellular matrix (ECM) remodeling in the developing fat pad. Indeed, the developing mesenchymal cell undergoes a dramatic alteration of cell morphology from stelate-shaped to sphere. These changes in cell morphology are paralleled by dramatic changes in the levels and the types of cytoskeletal, extracellular matrix and related components such as actin, fibronectin and collagen (Grégoire F. M. et al., 1998; Hausman, G. J. et al. 1996). Interestingly, adipose tissue contains a rich ECM, whose composition varies throughout life with changes in fat mass (Chun, T. et al., 2006; Gagnon, A. M., J. et al. 1998; Mehlhorn, A. T., P et al., 2006; Nakajima, I. S. et al. 2002).
The ECM not only influences the integrity of the structural system that supports cells, but also influences, via cell-surface receptors, cell-cell and cell-matrix interactions the molecular and signaling events that take place in the cells during the differentiation process. Thus, extracellular and intracellular events are coupled to regulate adipogenesis.
Storage of fat in adipose tissue is limited and exceeding this capacity leads to accumulation of lipids in others tissues, in particular in muscle, liver, and the endocrine pancreas, and to the secretion by adipocytes of various adipokines. The adipose tissue consists of several deposits located at different anatomical sites which may originate from distinct precursors and which have different physiological functions and pathophysiological roles. The visceral, as opposed to the subcutaneous adipose depots, may contribute more to the defects associated with the metabolic syndrome.
Cannabinoid 1 receptors have been identified in all organs playing a key role in glucose metabolism and type 2 diabetes, i.e. adipose tissue, the gastrointestinal tract, the liver, the skeletal muscle and the pancreas. Rimonabant, the first selective cannabinoid receptor 1 (CB1R) antagonist in clinical use, has been shown to reduce food intake and body weight thus improving glucose metabolism regulation.
However, there is still a need for novel therapeutic targets for the treatment of obesity.
Zinc finger, DHHC-type containing 2 proteins (Zdhhc2) has a palmitoyltransferase activity, and adds palmitic acid moiety to membrane receptors, integrin, caveolin and Wnt proteins (Oyama, T. et al., 2000; Fukumura, D. et al., 2003). As described above, Wnt proteins are involved in adipogenesis.
The inventors have now found that Zdhhc2 plays a critical role in adipocytes differentiation.
They propose that this enzyme is involved in adipocyte development by modifying signaling molecules or extracellular matrix proteins such as integrin. Extracellular matrix plasticity has recently been proposed to play an important role, not only for tissue integrity, but also for adipose tissue development. Therefore, Zdhhc2 might have a greater impact on extracellular matrix component and might have a role in the 3-dimensional development of adipose tissue. Furthermore, this protein is located at the cell membrane and could be a potential target for new drugs development.
Zdhhc2 is thus considered as a new relevant target for modulation of adipogenesis and for the treatment of obesity and related disorders. Inhibition of Zdhhc2 can also be used to decrease adipogenesis for reduction of subcutaneous and visceral fat accumulation.
The present invention is dawn to methods for regulating adipogenesis and metabolic function in adipocytes.
The present invention consists in the use of inhibitors of Zdhhc2 activity for modulation of adipogenesis, in particular for treatment of obesity and related disorders. The invention also concerns pharmaceutical composition containing such modulators of adipogenesis and related disorders and screening test for such modulators.
Through a transcriptomic approach, the inventors identified genes whose expression was correlated with body weight gain in cohorts of C57BI/6 mice fed a high fat diet. Then, they conducted a second analysis in order to evaluate the changes in gene expression induced by rimonabant treatment of the high fat diet fed mice. Genes which have never been described before in adipocyte biology, but which might be involved in important biological processes such as signaling, modification of extracellular matrix proteins, and gene transcription were retained. These genes could be important for adipogenesis especially since they might be involved in the mechanism by which rimonabant reduces fat mass in mice. In this context, Zdhhc2 was identified as involved in adipocytes metabolism, especially as a major player of extracellular matrix component modulation in link with the 3-dimensional development of adipose tissue. More generally, this gene appears to play a role in adipogenesis and control of adipose tissue development in obesity.
The present invention consists in identification of modulators of Zdhhc2 activity. Such modulators can be any compound or molecule able to modulate Zdhhc2 activity in particular small molecules, lipids and siRNA.
Modulators of Zdhhc2 activity can be identified by detecting the ability of an agent to modulate the activity of Zdhhc2. Inhibitors of Zdhhc2 are any compound able to reduce or inhibit, totally or partially, the activity of Zdhhc2. Inhibitors of Zdhhc2 include, but are not limited to, agents that interfere with the interaction of Zdhhc2 with its natural partner in the intracellular compartment and agents that reduce Zdhhc2 expression, both at transcriptional and translational levels.
CD9 and CD151 are two membrane proteins which specifically and directly interact with Zdhhc2. These proteins are able to bind integrins after palmytoylation by Zdhhc2 then allowing cell-cell attachment as described in Resh, M D et al. (2006) and Sharma C., et al. (2008). Therefore, modulators of Zdhhc2 activity can be tested in a screening that would be based on the presence on CD9 or CD151 of labeled palmitate residue due to the Zdhhc2 activity.
As an example, in one particular, embodiment a screening test can be performed as follows: membrane fraction from recombinant cells expressing CD9 or CD151 are prepared. This fraction is incubated with a sample containing Zdhhc2 activity (any source is suitable as extract from adipose tissue from patients, from animals or from recombinant cells) as well as labeled palmitate (as 3H palmitate) and a candidate compound. Then the palmitoylation activity of Zdhhc2 is measured by the quantification of labeled palmitate present on the target protein. For this step, the target protein (CD9, CD151 or any specific target for Zdhhc2) are immunoprecipitated using a specific antibody. The 3H emission detected in the retained fraction is quantified. As a result, the quantity of signal detected is proportional to the activity of Zdhhc2 present in the sample. Therefore, an inhibitor compound can be identified when a decrease in Zdhhc2 activity is measured compared to a control sample containing no candidate compound.
In another embodiment, the expression of Zdhhc2 is modulated through RNA interference, using small interfering RNAs (siRNA) or small hairpin RNAs (shRNAs). Therefore, in one aspect, the present invention relates to double stranded nucleic acid molecules including small nucleic acid molecules, such as short interfering nucleic acid (siNA), short interfering RNA (siRNA), double-stranded RNA (dsRNA), micro-RNA (miRNA), and short hairpin RNA (shRNA) molecules able to mediate RNA interference (RNAi) against Zdhhc2 gene expression, including cocktails of such small nucleic acid molecules and suitable formulations of such small nucleic acid molecules.
The phenomenon of RNAi mediated gene silencing has been described first in the Caenorhabditis elegans system, in which microinjection of long double stranded RNA molecules was reported. The mechanism of RNA mediated gene inactivation seems to be slightly different in the various organisms that have been investigated so far. However, in all systems, RNA mediated gene silencing is based on post-transcriptional degradation of the target mRNA induced by the endonuclease Argonaute2 which is part of the so called RISC complex. Sequence specificity of degradation is determined by the nucleotide sequence of the specific antisense RNA strand loaded into the RISC complex.
The introduction into cells of a siRNA compound results in cells having a reduced level of the target mRNA and, thus, of the corresponding polypeptide and, concurrently, of the corresponding enzyme activity.
siRNAs specific for Zdhhc2, as described herein, can be used as modulators of Zdhhc2 activity, in order to reduce the translation of Zdhhc2 mRNA. More particularly, siRNA specific for Zdhhc2 can be used to reduce adipogenesis and thus to treat obesity and related diseases.
In one embodiment, the invention features a double stranded nucleic acid molecule, such as a siRNA molecule, where one of the strands comprises nucleotide sequence having complementarity to a predetermined Zdhhc2 nucleotide sequence in a target Zdhhc2 nucleic acid molecule, or a portion thereof.
The RNA molecule can be used modified or unmodified. An example of modification is the incorporation of tricylo-DNA to allow improved serum stability of oligonucleotide.
In one embodiment, the predetermined Zdhhc2 nucleotide sequence is a Zdhhc2 nucleotide target sequence described herein (SEQ ID NO. 1 and SEQ ID NO. 3).
Due to the potential for sequence variability of the genome across different organisms or different subjects, selection of siRNA molecules for broad therapeutic applications likely involves the conserved regions of the gene. Thus in one embodiment, the present invention relates to siRNA molecules that target conserved regions of the genome or regions that are conserved across different targets. siRNA molecules designed to target conserved regions of various targets enable efficient inhibition of Zdhhc2 gene expression in diverse patient populations.
In one embodiment, the invention features a double-stranded short interfering nucleic acid molecule that down-regulates expression of a target Zdhhc2 gene or that directs cleavage of a target RNA, wherein said siRNA molecule comprises about 15 to about 28 base pairs, preferably 19 base pairs. A siRNA or RNAi inhibitor of the instant invention can be chemically synthesized, expressed from a vector or enzymatically synthesized.
In a particular embodiment, the siRNA specific for Zdhhc2 are shRNA having sequence SEQ ID NO. 5 or SEQ ID NO. 6. In a preferred embodiment, the siRNA specific for Zdhhc2 are shRNA having sequence SEQ ID NO. 5. The use of a siRNA according to the present invention leads to reduction of the mRNA level from 5% to 20%, preferably from 5% to 15%, more preferably from 5% to 10% of the mRNA level of the corresponding wild type cell. The wild type cell is the cell prior to the introduction of the nucleic acid encoding the siRNA compound, in which the targeted mRNA is not degraded by a siRNA compound.
Inhibitors of Zdhhc2 activity can be administrated by any suitable route, both locally or systemically depending on the nature of the molecule and the expected effect. SiRNA can be administrated locally in case of double strand molecule directly in the targeted tissue, or administrated through a vector in case of shRNA, according to protocols used in the art.
In one embodiment, RNAi is obtained using shRNA molecules. ShRNA constructs encode a stem-loop RNA. After introduction into cells, this stem-loop RNA is processed into a double stranded RNA compound, the sequence of which corresponds to the stem of the original RNA molecule. Such double stranded RNA can be prepared according to any method known in the art including vitro and in vivo methods as, but not limited to, described in Sahber et al (1987), Bhattacharyya et al, (1990) or U.S. Pat. No. 5,795,715.
For in vivo administration, shRNA can be introduced into a plasmid. Plasmid-derived shRNAs present the advantage to provide the option for combination with reporter genes or selection markers, and delivery via viral or non viral vectors. The introduction of shRNA into a vector and then into cells ensure that the shRNA is continuously expressed. The vector is usually passed on to daughter cells, allowing the gene silencing to be inherited.
The present invention also provides vectors comprising the polynucleotides for expression of shRNA expression of the invention. These vectors are for example AAV vector, retroviral vector in particular lentiviral vector, adenoviral vector which can be administered by different suitable routes including intravenous route, intramuscular route, direct injection into subcutaneous tissue or other targeted tissue chosen according to usual practice.
The route of administration of siRNA varies from local, direct delivery to systemic intravenous administration. The advantage of local delivery is that the doses of siRNA required for efficacy are substantially low since the molecules are injected into or near the target tissue. Local administration also allows for focused delivery of siRNA. For such direct delivery, naked siRNA can be used. “Naked siRNA” refers to delivery of siRNA (unmodified or modified) in saline or other simple excipients such as 5% dextrose. The ease of formulation and administration of such molecules makes this an attractive therapeutic approach. Naked DNA can also be formulated into lipids especially liposomes.
Systemic application of siRNA is often less invasive and, more importantly, not limited to tissues which are sufficiently accessible from outside. For systemic delivery, siRNA can be formulated with cholesterol conjugate, liposomes or polymer-based nanoparticules. Liposomes are traditionally used in order to provide increased pharmacokinetics properties and/or decreased toxicity profiles. They allow significant and repeated success in vivo delivery. Currently, use of lipid-based formulations of systemic delivery of siRNA, especially to hepatocytes, appears to represent one of the most promising near-term opportunities for development of RNAi therapeutics. Formulation with polymers such as dynamic polyconjugates—for example coupled to N-acetylglucosamine for hepatocytes targeting—and cyclodextrin-based nanoparticules allow both targeted delivery and endosomal escape mechanisms. Others polymers such as atelocollagen and chitosan allow therapeutic effects on subcutaneous tumor xenografts as well as on bone metastases.
SiRNA can also be directly conjugated with a molecular entity designed to help targeted delivery. Given the nature of the siRNA duplex, the presence of the inactive or sense stand makes for an ideal site for conjugation. Examples of conjugates are lipophilic conjugates such as cholesterol, or aptamer-based conjugates.
Cationic peptides and proteins are also used to form complexes with the negatively charged phosphate backbone of the siRNA duplex.
These different delivery approaches can be used to target the Zdhhc2 siRNA into the relevant tissue, especially adipose tissue. For such targeting, siRNA can be conjugated to different molecules interacting with pre-adipocytes and adipocytes, as for example ligands interacting with lipids transporters, receptors, insulin receptor or any molecule known in the art.
Another object of the invention is a pharmaceutical composition, which comprises, as active principle, a modulator of Zdhhc2 according to the present invention. These pharmaceutical compositions comprise an effective dose of at least one modulator according to the invention, and at least one pharmaceutically acceptable excipient. Said excipients are chosen according to the pharmaceutical form and the administration route desired, among usual excipients known of one of skill in the art.
The invention also consists in a method for modulation of adipogenesis. Such method can be used to treat obesity or related diseases. Such method can also be used in order to decrease fat accumulation in a cosmetic purpose.
Modulators of Zdhhc2 activity are useful in therapeutics to modulate adipogenesis, in particular in the treatment and prevention of obesity related disorders, in particular type 2 diabetes, dyslipidemia, elevated blood pressure, insulin resistance, cardiovascular disorders and more generally metabolic syndromes.
The present invention, according to another of its aspects, relates to a method for the treatment of the above pathologies, which comprises the in vivo administration to a patient of an effective dose of a modulator of Zdhhc2 according to the invention.
The appropriate unitary dosage forms comprise the oral forms, such as tablets, hard or soft gelatin capsules, powders, granules and oral solutions or suspensions, the sublingual, buccal, intratracheal, intraocular, intranasal forms, by inhalation, the topical, transdermal, sub-cutaneous, intramuscular or intra-venous forms, the rectal forms and the implants. For the topical application, the compounds of the invention may be used as creams, gels, ointments or lotions.
According to usual practice, the dosage suitable to each patient is determined by the physician according to the administration route, the weight and response of the patient.
Zdhhc2 inhibitors are also useful for cosmetic applications in order to reduce disgraceful fat accumulation.
For cosmetic applications, inhibitors of Zdhhc2 can be incorporated in a suitable formulation for topical use. The inhibitors of Zdhhc2 can both be small molecules or siRNA as previously described.
The invention is now described by reference to the following examples, which are illustrative only, and are not intended to limit the present invention.
C57BL/6J mice, which are obesity-prone (5), were fed for 6 months with a high fat diet (HFD). After 6 months of HFD, mice exhibited scattered body weights with various degrees of glucose intolerance (measured by a glucose tolerance test. The HFD mice were separated into 3 groups displaying the same level of glucose intolerance but with low (L), medium (M) or high (H) body weights and treated them, as well as normal chow (NC) fed mice, for one month with vehicle or rimonabant (10 mg·kg−1·day−1), to normalize their body weight. The treatment also normalized glucose tolerance, as described previously (25).
RNA Preparation, Labeling and Hybridization on cDNA Microarrays.
RNA from 5 different mice per group was extracted from visceral and subcutaneous adipose tissues using peqGOLD Trifast™ (peqlab) and chloroform-isoamylalcool (24:1) extraction. RNA was precipitated with isopropanol and purified by passage over RNeasy columns (Qiagen). RNA quality was checked before and after amplification with a Bioanalyzer 2100 (Agilent). RNA was reverse transcribed and RNA was amplified with MessageAmp™ kit (Ambion). A Mouse Universal Reference (Clontech) was similarly amplified and both adipose tissue and reference RNAs were labeled by an indirect technique with Cy5 and Cy3 according to published protocols (de Fourmestraux et al., J. Biol. Chem. 2004 279: 50743-53). Labeled RNAs were hybridized to microarrays containing 17664 cDNAs prepared at the DNA Array Facility of the University of Lausanne. Scanning, image, and quality control analyses were performed as previously published (de Fourmestraux et al., J. Biol. Chem. 2004 279:50743-53). Data were expressed as log2 intensity ratios (Cy5/Cy3), normalized with a print tip locally weighted linear regression (Lowess) method and filtered based on spot quality and incomplete annotation. All analyses were performed with the R software for statistical computing available at the Comprehensive R Archive Network (cran.us.r-project.org/).
3T3-L1 cells were cultured in DMEM (Gibco) with 10% FBS (Gibco) at 5% CO2. After retroviral infection (see below), cells were allow to grow to confluence in either 100-mm or 60-mm dishes in DMEM with 10% FBS. Once confluence was reached, cells were exposed to differentiation medium containing dexamethasone (1 μM), insulin (5 μg/ml), and isobutylmethylxanthine (0.5 μM) (DMI). After 2 days cells were maintained in medium containing insulin (5 μml) until ready for harvest at 7 days.
After 7 to 10 days of differentiation, cells were washed once in PBS and fixed with formaldehyde (Formalde-fresh; Fisher) for 15 minutes. The staining solution was prepared by dissolving 0.5 g oil-red-0 in 100 ml of isopropanol; 60 ml of this solution was mixed with 40 ml of distilled water. After 1 hour at room temperature the staining solution was filtered and added to dishes for 4 hours. The staining solution was then removed and cells were washed twice with distilled water.
shRNAs were constructed using the RNAi-Ready pSIREN-RetroQ ZsGreen (Clontech). Target sequences for Zdhhc2 were designed by querying the Whitehead siRNA algorithm (http://jura.wi.mit.edu/bioc/siRNAext/) as well as the siRNA designer software from Clontech (http://bioinfo.clontech.com/rnaidesigner/); at least two sequences represented by both algorithms were subcloned into the pSIREN vectors (Clontech) using the EcoRI and BamH1 restriction sites. The following target sequences for Zdhhc2 were chosen SEQ ID NO. 5 and 6 as a negative control, we used the following siRNA sequence against luciferase: SEQ ID NO. 7.
Transfection of shRNA Constructs
The specificity of shRNAs was tested in 293T HEK cells co-transfected using calcium-Phosphate methods described in (14) with expression vectors containing Zdhhc2 cDNA and the RNAi-Ready pSIREN-RetroQ ZsGreen vector expressing either the shRNA against lucifeare (control shLUC) or Zdhhc2 (shZdhhc2). RT-PCR analysis was performed on cell RNA-extraction 24 h after transfection.
Generation of Retro Viral Constructs and Retro Viral Infections
Retroviruses were constructed in the RNAi-Ready pSIREN-RetroQ ZsGreen (pSIREN Clontech). Viral constructs were transfected using calcium-phosphate method described in Jordan, M. et al. (2004) into 293 HEK packaging cells along with constructs encoding gag-pol and the VSV-G protein. Supernatants were harvested after 48 h in presence of 3 μm of Trichostatin A (Sigma) and either used immediately or snap frozen and stored at −80° C. for later use. Viral supernatants were added to the cells for 6 hours in the presence of polybrene (4 μg/ml) and diluted two times with fresh medium for the next 15 hours.
Isolation of Adipocytes and Stromal Vascular Fraction (SVF) from Adipose Tissue
Eight week-old male C57BL/6J mice (n=6-8) were euthanized by CO2 inhalation and epididymal (visceral) and subcutaneous adipose tissue were collected and placed in DMEM medium containing 10 mg/mL fatty acid-poor BSA (Sigma-Aldrich, St. Louis, Mich.). The tissue was minced into fine pieces and then digested in 0.12 units/mL collagenase type I (Sigma) at 37° C. in a shaking water bath (80 Hz) for 1 hour. Samples were then filtered through a sterile 250 μm nylon mesh (Scrynel NY250HC, Milian) to remove undigested fragments. The resulting suspension was centrifuged at 1100 RPM for 10 min to separate SVF from adipocytes. Adipocytes were removed and washed with DMEM buffer. They were then suspended in peqGOLD TriFast reagent (Axonlab) and RNA was isolated according to the manufacturer's instructions. The SVF fraction was incubated in erythrocyte lysis buffer (0.154 mM NH4Cl, 10 mM KHCO3, 0.1 mM EDTA) for 2 min. Cells were then centrifuged at 1100 RPM for 10 min and re-suspended in 500 μl of peqGOLD TriFast reagent (Axonlab) for RNA isolation.
RNA Extraction and Real-Time PCR
Total RNA was isolated from cultured cells using peqGOLD TriFast reagent according to the manufacturer's instructions (Axonlab). First strand cDNA was synthesized from 0.5 μg of total RNA using random primers and Superscript II (Invitrogen). Real time PCR was performed using Power SYBR Green Mix (Applied Biosystem). The following primers were used for mouse genes: mZdhhc2-F (SEQ ID NO. 8) and mZdhhc2-R (SEQ ID NO.9) for Zdhhc2; Ap2-F (SEQ ID NO. 16); Ap2-R (SEQ ID NO. 17) for; mCyclophilinA-F (SEQ ID NO. 12); mCyclophilinA-R (SEQ ID NO. 13), mCyclophilin A-F (SEQ ID NO.12); mCyclophilin A-R (SEQ ID NO. 13). The following primers were used for human genes: hZdhhc2-F SEQ ID NO. 10; hZdhhc2-R SEQ ID NO. 11 hCyclophilin A-F SEQ ID NO. 14; hCyclophilin A-R SEQ ID NO. 15.
Total RNA from various mouse tissues was isolated using the peqGOLD TriFast reagent according to the manufacturer's instructions (Axonlab). Total RNA (8 μg) was separated on a 1.2% agarose/formaldehyde gel and transfected overnight to a nylon membrane. To control for RNA quantity loading, the membrane was stained with methylene blue prior the subsequent hybridizations. For the detection of Zdhh2 signals, probes from the full-length cDNA mouse plasmid (Open Biosystem) were used. The probes were labeled by random priming with [α-32P]dCTP (Amersham). Hybridization and washing were carried out using the Quickhib method according to manufacturer's instructions (Stratagene). Blots were exposed to Hyperfilm ECL (Amersham) at −80° C. for 1 day or several days depending on the signal intensity.
Bioinformatic analysis of the microarray data was performed to identify genes that fulfilled the three following criteria: (i) regulated by high fat feeding, (ii) similar regulated expression by high fat feeding in both visceral (VAT) and subcutaneous fat (SCAT) and (iii) similar normalization of their expression by rimonabant treatment (FIG. 1). Out of the ˜17,000 gene targets present on the cDNA microarray used, 34 genes fulfilled these criteria, which are listed in Table 1. Remarkably, 10 of these genes—Cav1, Fgf1, Fndc3b, Kif5b, Mest, Npr3, Pik3ca, Sparc, Vldlr, and Wwtr1—were previously known to be important regulators of adipose tissue development and function. Some of these genes had expression levels correlated with body weight gain (shown in grey in Table 1), suggesting a potential role in hyperplasia and/or hypertrophy of adipose tissues during obesity. These results validate the approach used to identify possible novel targets for therapeutic treatment of obesity.
Most importantly, many of the genes cited in table 1 have never been studied in the context of in adipose tissue development or biology. These genes belong to the following classes of function: extracellular matrix/cell interaction, cytoskeleton, intracellular signaling, enzymes, and transcription factors/co-factors. They are likely involved in tissue remodeling, and particularly in adipocyte development. One of these genes, Zdhhc2 gene and it role in adipocyte biology, is presented herein and constitutes one aspect of the present invention.
Zdhhc2 has a palmitoyltransferase activity, and adds palmitic acid moiety to membrane receptors, integrin, caveolin and Wnt proteins (23, 6). Wnt proteins are involved in adipogenesis. Thus, this enzyme might be involved in adipocyte development by modifying signaling molecules or extracellular matrix proteins such as integrin. Extracellular matrix plasticity has recently been proposed to play an important role, not only for tissue integrity, but also for adipose tissue development, (20, 7, 19). The study of Zdhhc2 is therefore of major interest in light of this emerging concept.
To better understand the role of Zdhhc2 in adipocytes development, its pattern of expression was first characterized. mRNA levels were measured by northern-blot and RT-PCR in various mouse tissues, in isolated preadipocytes and adipocytes, in visceral adipose tissue (VAT) and subcutaneous adipose tissue (SCAT) of mouse obesity model (Ob/Ob mice) and in human adipose tissues.
By RT-PCR, it was shown that Zdhhc2 is strongly expressed in heart, BAT, SCAT, VAT spleen and muscle, whereas the expression of Zdhhc2 is weaker in lung and kidney and very weak in liver (FIG. 2A). It was also demonstrated that Zdhhc2 level is increased in white adipose tissues of Ob/Ob mice, compared to level in wild type mice (FIG. 2B). Values are expressed as fold increase relative to the control values in SCAT set arbitrarily at 1.
Adipose tissue is a complex tissue that includes not only mature adipocytes, but also precursor cells such as preadipocytes as well as blood vessels, macrophages and fibroblastic cells. Based on a collagenase I digestion technique, stromal vascular fraction (SVF) (including preadipocyte, endothelial and macrophage cells) was separated from the isolated adipocyte fraction. It was found that Zdhhc2 is expressed in both fractions, SVF and isolated adipocytes (FIG. 2C). These results indicate that Zdhhc2 is involved in differentiation and/or proliferation processes but also in immature adipocyte biology.
The next step was to determine whether Zdhhc2 gene is conserved among species. To address this question, a RT-PCR was performed on human adipose tissue samples. Preadipocytes and adipocytes were isolated from SCAT or VAT. Isolated preadipocytes were induced to differentiate in vitro until day 7. Results showed that Zdhhc2 is indeed expressed in human fat (FIG. 2D). They indicate that these genes are present in human adipose tissues. Altogether these results suggest that Zdhhc2 is a relevant candidate gene for adipocytes development, especially for adipogenesis or fat tissue enlargement in obesity.
Next, the expression of Zdhhc2 gene was assessed during adipogenesis. For that purpose, mRNA levels were measured by RT-PCR during a detailed differentiation time-course of 3T3-L1 (an adipogenic cell line) (FIG. 2E). The experiment showed that Zdhhc2 expression is induced at very early times after DMI treatment (between 15 minutes-1 hour) and then remains at low levels during the differentiation.
For the loss-of-function studies, shRNA specific for Zdhhc2 subcloned into a retroviral vector from Clontech were used (RNAi-Ready pSIREN-RetroQ ZsGreen or pSIREN). This plasmid contains a GFP marker, which allows controlling the infection efficiency in 3T3-L1 cells. Two different shRNA for Zdhhc2, were cloned into the pSIREN plasmid, and were first tested in 293T HEK cells. This experiment demonstrated the ability of shRNA specific for Zdhhc2 to inhibit Zdhhc2 expression. Interestingly, 60% and 50% of knockdown were obtained respectively with shZdhhc2-1 and shZdhhc2-2 (FIG. 3A), which have been used for transduction into 3T3-L1 cells.
3T3-L1 cells were then infected for 6 hours with retroviral vectors expressing shRNA directed towards either Zdhhc2 (shZdhhc2) or luciferase (shLuc). Using the GFP marker, we observed 90 to 95% infection in the 3T3-L1 cells (data not shown). Then, cells were allowed to reach confluence and to differentiate with DMI treatment. After 9 days of differentiation, cells were stained to determine the amount of lipid content with oil-red-O staining. This experiment evidences that knockdown of Zdhhc2 inhibits adipogenesis in vitro as shown by oil-red-O staining and aP2 expression at day 9 (FIG. 2B), which is decreased by 75 and 60% in ShZdhhc2-1 and shZdhhc2-2 infected 3T3-L1 cells respectively (FIG. 2C). As a control, no inhibition was obtained with shLuc.