Cartilage-Specific Overexpression of ERRγ Results in Chondrodysplasia and Reduced Chondrocyte Proliferation

While the role of estrogen receptor-related receptor alpha (ERRα) in chondrogenesis has been investigated, the involvement of ERR gamma (ERRγ) has not been determined. To assess the effect of increased ERRγ activity on cartilage development in vivo, we generated two transgenic (Tg) lines overexpressing ERRγ2 via a chondrocyte-specific promoter; the two lines exhibited ∼3 and ∼5 fold increased ERRγ2 protein expression respectively in E14.5 Tg versus wild type (WT) limbs. On postnatal day seven (P7), we observed a 4–10% reduction in the size of the craniofacial, axial and appendicular skeletons in Tg versus WT mice. The reduction in bone length was already present at birth and did not appear to involve bones that are derived via intramembranous bone formation as the bones of the calvaria, clavicle, and the mandible developed normally. Histological analysis of P7 growth plates revealed a reduction in the length of the Tg versus WT growth plate, the majority of which was attributable to a reduced proliferative zone. The reduced proliferative zone paralleled a decrease in the number of Ki67-positive proliferating cells, with no significant change in apoptosis, and was accompanied by large cell-free swaths of cartilage matrix, which extended through multiple zones of the growth plate. Using a bioinformatics approach, we identified known chondrogenesis-associated genes with at least one predicted ERR binding site in their proximal promoters, as well as cell cycle regulators known to be regulated by ERRγ. Of the genes identified, Col2al, Agg, Pth1r, and Cdkn1b (p27) were significantly upregulated, suggesting that ERRγ2 negatively regulates chondrocyte proliferation and positively regulates matrix synthesis to coordinate growth plate height and organization.     

Design,synthesis, and evaluation of simple phenol amides as ERRγ agonists

Herein we report the design and synthesis of a series of simple phenol amide ERRγ agonists based on a hydrazone lead molecule. Our structure activity relationship studies in this series revealed the phenol portion of the molecule to be required for activity. Attempts to replace the hydrazone with more suitable chemotypes led to a simple amide as a viable alternative. Differential hydrogen-deuterium exchange experiments were used to help understand the structural basis for binding to ERRγ and aid in the development of more potent ligands.     

The Asymmetric Binding of PGC-1α to the ERRα and ERRγ Nuclear Receptor Homodimers Involves a Similar Recognition Mechanism

Background

PGC-1α is a crucial regulator of cellular metabolism and energy homeostasis that functionally acts together with the estrogen-related receptors (ERRα and ERRγ) in the regulation of mitochondrial and metabolic gene networks. Dimerization of the ERRs is a pre-requisite for interactions with PGC-1α and other coactivators, eventually leading to transactivation. It was suggested recently (Devarakonda et al) that PGC-1α binds in a strikingly different manner to ERRγ ligand-binding domains (LBDs) compared to its mode of binding to ERRα and other nuclear receptors (NRs), where it interacts directly with the two ERRγ homodimer subunits.

Methods/Principal Findings

Here, we show that PGC-1α receptor interacting domain (RID) binds in an almost identical manner to ERRα and ERRγ homodimers. Microscale thermophoresis demonstrated that the interactions between PGC-1α RID and ERR LBDs involve a single receptor subunit through high-affinity, ERR-specific L3 and low-affinity L2 interactions. NMR studies further defined the limits of PGC-1α RID that interacts with ERRs. Consistent with these findings, the solution structures of PGC-1α/ERRα LBDs and PGC-1α/ERRγ LBDs complexes share an identical architecture with an asymmetric binding of PGC-1α to homodimeric ERR.

Conclusions/Significance

These studies provide the molecular determinants for the specificity of interactions between PGC-1α and the ERRs, whereby negative cooperativity prevails in the binding of the coactivators to these receptors. Our work indicates that allosteric regulation may be a general mechanism controlling the binding of the coactivators to homodimers.     

SIRT4 Represses Peroxisome Proliferator-Activated Receptor α Activity To Suppress Hepatic Fat Oxidation

Sirtuins are a family of protein deacetylases, deacylases, and ADP-ribosyltransferases that regulate life span, control the onset of numerous age-associated diseases, and mediate metabolic homeostasis. We have uncovered a novel role for the mitochondrial sirtuin SIRT4 in the regulation of hepatic lipid metabolism during changes in nutrient availability. We show that SIRT4 levels decrease in the liver during fasting and that SIRT4 null mice display increased expression of hepatic peroxisome proliferator-activated receptor α (PPARα) target genes associated with fatty acid catabolism. Accordingly, primary hepatocytes from SIRT4 knockout (KO) mice exhibit higher rates of fatty acid oxidation than wild-type hepatocytes, and SIRT4 overexpression decreases fatty acid oxidation rates. The enhanced fatty acid oxidation observed in SIRT4 KO hepatocytes requires functional SIRT1, demonstrating a clear cross talk between mitochondrial and nuclear sirtuins. Thus, SIRT4 is a new component of mitochondrial signaling in the liver and functions as an important regulator of lipid metabolism.     

Innate IFN-γ is essential for programmed death ligand-1-mediated T cell stimulation following Listeria monocytogenes infection

Although best characterized for sustaining T cell exhaustion during persistent viral infection, programmed death ligand-1 (PDL-1) also stimulates the expansion of protective T cells after infection with intracellular bacterial pathogens. Therefore, establishing the molecular signals that control whether PDL-1 stimulates immune suppression or activation is important as immune modulation therapies based on manipulating PDL-1 are being developed. In this study, the requirement for PDL-1 blockade initiated before infection with the intracellular bacterium Listeria monocytogenes in reducing pathogen-specific T cell expansion is demonstrated. In turn, the role of proinflammatory cytokines triggered early after L. monocytogenes infection in controlling PDL-1-mediated T cell stimulation was investigated using mice with targeted defects in specific cytokines or cytokine receptors. These experiments illustrate an essential role for IL-12 or type I IFNs in PDL-1-mediated expansion of pathogen-specific CD8(+) T cells. Unexpectedly, direct stimulation by neither IL-12 nor type I IFNs on pathogen-specific CD8(+) cells was essential for PDL-1-mediated expansion. Instead, the absence of early innate IFN-γ production in mice with combined defects in both IL-12 and type I IFNR negated the impacts of PDL-1 blockade. In turn, IFN-γ ablation using neutralizing Abs or in mice with targeted defects in IFN-γR each eliminated the PDL-1-mediated stimulatory impacts on pathogen-specific T cell expansion. Thus, innate IFN-γ is essential for PDL-1-mediated T cell stimulation.     

MiR130b-Regulation of PPARγ Coactivator- 1α Suppresses Fat Metabolism in Goat Mammary Epithelial Cells

Fat metabolism is a complicated process regulated by a series of factors. microRNAs (miRNAs) are a class of negative regulator of proteins and play crucial roles in many biological processes; including fat metabolism. Although there have been some researches indicating that miRNAs could influence the milk fat metabolism through targeting some factors, little is known about the effect of miRNAs on goat milk fat metabolism. Here we utilized an improved miRNA detection assay, S-Poly-(T), to profile the expression of miRNAs in the goat mammary gland in different periods, and found that miR-130b was abundantly and differentially expressed in goat mammary gland. Additionally, overexpressing miR-130b impaired adipogenesis while inhibiting miR-130b enhanced adipogenesis in goat mammary epithelial cells. Utilizing 3’-UTR assay and Western Blot analusis, the protein peroxisome proliferator-activated receptor coactivator-1α (PGC1α), a major regulator of fat metabolism, was demonstrated to be a potential target of miR-130b. Interestingly, miR-130b potently repressed PGC1α expression by targeting both the PGC1α mRNA coding and 3’ untranslated regions. These findings have some insight of miR-130b in mediating adipocyte differentiation by repressing PGC1α expression and this contributes to further understanding about the functional significance of miRNAs in milk fat synthesis.     

ERRγ Promotes Angiogenesis,Mitochondrial Biogenesis,and Oxidative Remodeling in PGC1α/β-Deficient Muscle

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Hyperthermia-induced Hsp90·eNOS Preserves Mitochondrial Respiration in Hyperglycemic Endothelial Cells by Down-regulating Glut-1 and Up-regulating G6PD Activity

Uncoupling of NO production from NADPH oxidation by endothelial nitric-oxide synthase (eNOS) is enhanced in hyperglycemic endothelium, potentially due to dissociation of heat shock proteins 90 (Hsp90), and cellular glucose homeostasis is enhanced by a ROS-induced positive feed back mechanism. In this study we investigated how such an uncoupling impacts oxygen metabolism and how the oxidative phosphorylation can be preserved by heat shock (42 °C for 2 h, hyperthermia) in bovine aortic endothelial cells. Normal and heat-shocked bovine aortic endothelial cells were exposed to normoglycemia (NG, 5.0 mm) or hyperglycemia (30 mm). With hyperglycemia treatment, O₂ consumption rate was reduced (from V_O2max = 7.51 ± 0.54 to 2.35 ± 0.27 mm Hg/min/10⁶ cells), whereas in heat-shocked cells, O₂ consumption rate remained unaltered (8.19 ± 1.01 mm Hg/min/10 × 10⁶ cells). Heat shock was found to enhance Hsp90/endothelial NOS interactions and produce higher NO. Moreover, ROS generation in the hyperglycemic condition was also reduced in heat-shocked cells. Interestingly, glucose uptake was reduced in heat-shocked cells as a result of decrease in Glut-1 protein level. Glucose phosphate dehydrogenase activity that gives rise to NADPH generation was increased by hyperthermia, and mitochondrial oxidative metabolism was preserved. In conclusion, the present study provides a novel mechanism wherein the reduced oxidative stress in heat-shocked hyperglycemic cells down-regulates Glut-1 and glucose uptake, and fine-tuning of this pathway may be a potential approach to use for therapeutic benefit of diabetes mellitus.     

The Potent Anti-HIV Activity of CXCL12γ Correlates with Efficient CXCR4 Binding and Internalization

We previously demonstrated that the naturally occurring splice variant stromal cell-derived factor 1γ/CXCL12γ is the most potent CXCL12 isoform in blocking X4 HIV-1, with weak chemotactic activity. A conserved BBXB domain (B for basic and X for any residue) located in the N terminus (²⁴KHLK²⁷) is found in all six isoforms of CXCL12. To determine whether the potent antiviral activity of CXCL12γ is due to the presence of the extra C-terminal BBXB domains, we mutated each domain individually as well as in combination. Although binding of CXCL12γ to heparan sulfate proteoglycan (HSPG) was 10-fold higher than that observed with CXCL12α, the results did not demonstrate a direct correlation between HSPG binding and the potent antiviral activity. CXCL12γ mutants lacking the conserved BBXB domain (designated γB1) showed increased binding to HSPG but reduced anti-HIV activity. In contrast, the mutants lacking the C-terminal second and/or third BBXB domain but retaining the conserved domain (designated B2, B3, and B23) showed decreased binding to HSPG but increased anti-HIV activity. The B2, B3, and B23 mutants were associated with enhanced CXCR4 binding, receptor internalization, and restored chemotaxis. Internalization of CXCR4 was more potent with CXCL12γ than with CXCL12α and was significantly reduced when the conserved BBXB domain was mutated. We concluded that the observed potent anti-HIV-1 activity of CXCL12γ is due to increased affinity for CXCR4 and to efficient receptor internalization.Chemokines are small, structurally related chemoattractant cytokines characterized by conserved cysteine residues. Based on the positions of the first N-terminal cysteines, chemokines fall into four subfamilies. The CC and CXC subfamilies have been well characterized. The CC subfamily includes the following: regulated on activation, normal T-cell expressed and secreted (RANTES), monocyte chemoattractant protein 1 (MCP-1), and macrophage inflammatory peptides 1 (MIP-1). The prototype of the CXC subfamily is interleukin-8 (IL-8)/CXCL8. The C chemokine (lymphotactine) and CX3C chemokine (fractalkine) subfamilies were recently identified (reviewed in reference 30). The physiological activities of chemokines are mediated by the selective recognition and activation of chemokine receptors belonging to the seven-membrane-domain G-protein-coupled receptor superfamily (GPCRs). In addition, chemokines also bind to glycosaminoglycans (GAGs) through distinct binding sites. Chemokine binding to GAGs on cells, particularly endothelial cells, results in chemotactic chemokine gradients that allow correct presentation of chemokines to leukocytes, therefore enabling target cells to cross the endothelial barrier and migrate into tissues (reviewed in reference 10).Stromal cell-derived factor 1 (SDF-1)/CXCL12 is a member of the CXC chemokine family and is a key regulator of B-cell lymphopoiesis, hematopoietic stem cell mobilization, and leukocyte migration (reviewed in reference 10). CXCL12 was originally thought to mediate these processes through the single receptor CXCR4 (9). However, later studies demonstrated that RDC-1/CXCR7 is also a receptor for CXCL12 (6, 11). CXCL12 has also been shown to block HIV-1 infection (5). There are two known human splice variants of CXCL12, referred to as CXCL12α and CXCL12β (27). The genomic structure of the CXCL12 gene revealed that human CXCL12α and CXCL12β are encoded by a single gene and arise by alternative splicing. The cDNAs corresponding to CXCL12α and CXCL12β encode proteins of 89 and 93 amino acids, respectively. A third splice variant, classified as CXCL12γ, has been identified in rats (14). The human equivalent of CXCL12γ was recently identified among other splice variants of CXCL12 (33). The novel human splice variants CXCL12γ, CXCL12ɛ, CXCL12δ, and CXCL12θ (also reported as CXCL12ϕ [33]) are expressed through alternative splicing events that result in different exons being added to the same first three exons. Therefore, all six splice variants of CXCL12 are identical in the first 88 amino acid residues from the amino terminus.It has been demonstrated that CXCL12α and -β are expressed in numerous tissues, with the highest expression levels in the liver, pancreas, and spleen (33). The mRNA encoding CXCL12γ was detectable in the adult human heart but hardly detectable in several other tissues. On the other hand, CXCL12δ, -ɛ, and -θ could be detected in several human adult and fetal tissues, with the pancreas expressing the highest levels (33). Recent studies have demonstrated the tissue expression of CXCL12γ in the adult heart (24). We previously demonstrated that CXCL12γ is the most potent anti-HIV-1 inhibitor, with the weakest chemotactic activity and no detectable enhancing activity for hematopoietic progenitor cell survival or replating capacity (2). The first three exons present in the CXCL12γ splice variant are identical to those found in CXCL12α and CXCL12β. The fourth exon, however, contains a large number of basic residues that result in at least four additional BBXB domains in addition to the conserved ²⁴KHLK²⁷ domain (33). It is not known whether the additional BBXB domains in the C terminus of CXCL12γ result in higher affinity for heparan sulfate proteoglycan (HSPG) and whether differences in HSPG binding could explain the observed anti-HIV-1 potency or the low chemotactic activity.The BBXB motif on RANTES has been suggested as the principal site for high-affinity binding to heparan sulfate. This binding controls receptor selectivity (22). It was previously demonstrated that a mutation of CXCL12α in the ²⁴KHLK²⁷ domain reduces the antiviral activity at least 50 percent without affecting the chemotactic activity (4, 29). It was proposed that chemokine binding to HSPG might concentrate the chemokine near the CXCR4 receptor or form a haptotactic chemokine gradient.In this study, we analyzed the mechanism of the potent antiviral activity of CXCL12γ. We examined the role of the additional BBXB domains of CXCL12γ in the observed biological activities of CXCL12γ. Mutations in CXCL12γ were introduced to knock out the BBXB domains either individually or in combination. We analyzed receptor internalization and binding affinities of the mutant chemokines for CXCR4 and HSPG. The results demonstrate that the potent anti-HIV activity of CXCL12γ is due to its efficient binding and internalization of CXCR4. The results provide important insight into the structure-function relationship of CXCL12γ and suggest that determinants other than the BBXB domains are involved in the observed biological activities of CXCL12γ.     

Expression of Recombinant Human Interferon-γ with Antiviral Activity in the Bi-Cistronic Baculovirus-Insect/Larval System

A bi-cistronic baculovirus-insect/larval system containing a polyhedron promoter, an internal ribosome entry site (IRES), and an egfp gene was developed as a cost-effective platform for the production of recombinant human interferon gamma (rhIFN-γ). There was no significant difference between the amounts of rhIFN-γ produced in the baculovirus-infected Spodoptera frugiferda 21 cells grown in serum-free medium and the serum-supplemented medium, while the Trichoplusia ni (T. ni) and Spodoptera exigua (S. exigua) larvae afforded rhIFN-γ amounting to 1.08±0.04 and 9.74±0.35 μg/mg protein respectively. The presence of non-glycosylated and glycosylated rhIFN-γ was confirmed by immunoblot and lectin blot. The immunological activity of purified rhIFN-γ, with 96% purity by Nickel (II)-nitrilotriacetic acid (Ni-NTA) affinity chromatography, was similar to that commercially available. Moreover, the rhIFN-γ protein from T. ni had more potent antiviral activity. These findings suggest that this IRES-based expression system is a simple and inexpensive alternative for large-scale protein production in anti-viral research.     

Hesperidin Produces Cardioprotective Activity via PPAR-γ Pathway in Ischemic Heart Disease Model in Diabetic Rats

The present study investigated the effect of hesperidin, a natural flavonoid, in cardiac ischemia and reperfusion (I/R) injury in diabetic rats. Male Wistar rats with diabetes were divided into five groups and were orally administered saline once daily (IR-sham and IR-control), Hesperidin (100 mg/kg/day; IR-Hesperidin), GW9962 (PPAR-γ receptor antagonist), or combination of both for 14 days. On the 15^th day, in the IR-control and IR-treatment groups, rats were subjected to left anterior descending (LAD) coronary artery occlusion for 45 minutes followed by a one-hour reperfusion. Haemodynamic parameters were recorded and rats were sacrificed; hearts were isolated for biochemical, histopathological, ultrastructural and immunohistochemistry. In the IR-control group, significant ventricular dysfunctions were observed along with enhanced expression of pro-apoptotic protein Bax. A decline in cardiac injury markers lactate dehydrogenase activity, CK-MB and increased content of thiobarbituric acid reactive substances, a marker of lipid peroxidation, and TNF-α were observed. Hesperidin pretreatment significantly improved mean arterial pressure, reduced left ventricular end-diastolic pressure, and improved both inotropic and lusitropic function of the heart (+LVdP/dt and –LVdP/dt) as compared to IR-control. Furthermore, hesperidin treatment significantly decreased the level of thiobarbituric acid reactive substances and reversed the activity of lactate dehydrogenase towards normal value. Hesperidin showed anti-apoptotic effects by upregulating Bcl-2 protein and decreasing Bax protein expression. Additionally, histopathological and ultrastructural studies reconfirmed the protective action of hesperidin. On the other hand, GW9662, selective PPAR-γ receptor antagonist, produced opposite effects and attenuated the hesperidin induced improvements. The study for the first time evidence the involvement of PPAR-γ pathway in the cardioprotective activity of hesperidin in I/R model in rats.