Mechanisms underlying hypertriglyceridemia in rats with monosodium l-glutamate-induced obesity: Evidence of XBP-1/PDI/MTP axis activation

Non-alcoholic fatty liver disease (NAFLD) is intimately associated with insulin resistance and hypertriglyceridemia, whereas many of the mechanisms underlying this association are still poorly understood. In the present study, we investigated the relationship between microsomal triglyceride transfer protein (MTP) and markers of endoplasmic reticulum (ER) stress in the liver of rats subjected to neonatal monosodium l-glutamate (MSG)-induced obesity. At age 120 days old, the MSG-obese animals exhibited hyperglycemia, hypertriglyceridemia, insulin resistance, and liver steatosis, while the control (CTR) group did not. Analysis using fast protein liquid chromatography of the serum lipoproteins revealed that the triacylglycerol content of the very low-density lipoprotein (VLDL) particles was twice as high in the MSG animals compared with the CTR animals. The expression of ER stress markers, GRP76 and GRP94, was increased in the MSG rats, promoting a higher expression of X-box binding protein 1 (XBP-1), protein disulfide isomerase (PDI), and MTP. As the XBP-1/PDI/MTP axis has been suggested to represent a significant lipogenic mechanism in the liver response to ER stress, our data indicate that hypertriglyceridemia and liver steatosis occurring in the MSG rats are associated with increased MTP expression.     

Effect of Oxidation on the Structure of Human Low- and High-Density Lipoproteins

This work presents a controlled study of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) structural changes due to in vitro oxidation with copper ions. The changes were studied by small-angle x-ray scattering (SAXS) and dynamic light scattering (DLS) techniques in the case of LDL and by SAXS, DLS, and Z-scan (ZS) techniques in the case of HDL. SAXS data were analyzed with a to our knowledge new deconvolution method. This method provides the electron density profile of the samples directly from the intensity scattering of the monomers. Results show that LDL particles oxidized for 18 h show significant structural changes when compared to nonoxidized particles. Changes were observed in the electrical density profile, in size polydispersity, and in the degree of flexibility of the APO-B protein on the particle. HDL optical results obtained with the ZS technique showed a decrease of the amplitude of the nonlinear optical signal as a function of oxidation time. In contrast to LDL results reported in the literature, the HDL ZS signal does not lead to a complete loss of nonlinear optical signal after 18 h of copper oxidation. Also, the SAXS results did not indicate significant structural changes due to oxidation of HDL particles, and DLS results showed that a small number of oligomers formed in the sample oxidized for 18 h. All experimental results for the HDL samples indicate that this lipoprotein is more resistant to the oxidation process than are LDL particles.     

SAR study and conformational analysis of a series of novel peptide G protein‐coupled receptor kinase 2 inhibitors

G protein‐coupled receptor kinase 2 (GRK2) plays a central role in the cellular transduction network. In particular, during chronic heart failure GRK2 is upregulated and believed to contribute to disease progression. Thereby, its inhibition offers a potential therapeutic solution to several pathological conditions. In the present study, we performed a SAR study and a NMR conformational analysis of peptides derived from HJ loop of GRK2 and able to selectively inhibit GRK2. From Ala‐scan and d ‐Ala point replacement, we found that Arg residues don't affect the inhibitory properties, while a d ‐amino acid at position 5 is key to the activity. Conformational analysis identified two β‐turns that involve N‐terminal residues, followed by a short extended region. These information can help the design of peptides and peptido‐mimetics with enhanced GRK2 inhibition properties. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 121–128, 2014.     

Yeasts isolated from olive mill wastewaters from southern Italy: technological characterization and potential use for phenol removal

Olive mill wastewater (OMW) samples from two traditional varieties (Peranzana and Ogliarola Garganica) of Apulian region (southern Italy) and produced through continuous and traditional methods were microbiologically and chemically examined; thus, 104 yeasts were isolated and selected for further analyses. The strains were identified as Candida boidinii, Pichia holstii, Pichia membranifaciens, and Saccharomyces cerevisiae and analyzed to assess their suitability to metabolize phenols. Based on phenol metabolism, 27 strains were selected and inoculated into OMW aliquots to determine their ability to reduce phenols in vivo; then, five strains (identified with the codes 682—C. boidinii and 625, 642, 647, and 941—P. holstii) were used as a cocktail in wastewaters for a final validation step. In this last experiment, the effects of the temperature (10–30°C) and (NH₄)₂SO₄ (0.0–6.0 g l⁻¹) were studied through a central composite design approach, and the results highlighted that the cocktail was able to reduce phenols by 40% at 10°C with 6.0 g l⁻¹ of (NH₄)₂SO₄ added.     

Human liver peroxisomal alanine:glyoxylate aminotransferase: Different stability under chemical stress of the major allele,the minor allele,and its pathogenic G170R variant

The sensitivity to denaturant stress of the major (AGT-Ma) and the minor (AGT-Mi) allele of alanine:glyoxylate aminotransferase and P11L mutant has been examined by studying their urea-induced equilibrium unfolding processes with various spectroscopic and analytical techniques. AGT-Ma loses pyridoxal 5′-phosphate (PLP) and unfolds completely without exposing significant hydrophobic clusters through a two-state model (C_m ∼ 6.9 M urea). Instead, the unfolding of AGT-Mi and P11L variant proceeds in two steps. The first transition (C_m ∼ 4.6 M urea) involves PLP release, dimer dissociation and exposure of hydrophobic patches leading to a self-associated intermediate which is converted to an unfolded monomer in the second step. The unfolding pathways of apoAGT-Mi and apoP11L are similar to each other, but different from that of apoAGT-Ma. Notably, the monomerization step in apoAGT-Mi and apoP11L occurs with a C_m value (∼1.6 M urea) lower than in apoAGT-Ma (∼2.4 M urea). These data indicate that Pro11 is relevant for the stability of both the dimeric structure and the PLP binding site of AGT. Moreover, to understand the pathogenic consequences of G170R mutation on AGT-Mi at the protein level, G170R-Mi has been characterized. HoloG170R-Mi exhibits spectroscopic and catalytic features and urea unfolding profiles comparable to those of AGT-Mi, while the apo form monomerizes with a C_m of ∼1.1 M urea. These biochemical results are discussed in the light of the characteristics of the enzymatic phenotype of PH1 patients bearing G170R mutation in AGT-Mi and the positive response of these patients to pyridoxine treatment.     

Relationship between endoplasmic reticulum- and Golgi-associated calcium homeostasis and 4-NQO-induced DNA repair in Saccharomyces cerevisiae

Calcium (Ca²⁺) is an important ion that is necessary for the activation of different DNA repair mechanisms. However, the mechanism by which DNA repair and Ca²⁺ homeostasis cooperate remains unclear. We undertook a systems biology approach to verify the relationship between proteins associated with Ca²⁺ homeostasis and DNA repair for Saccharomyces cerevisiae. Our data indicate that Pmr1p, a Ca²⁺ transporter of Golgi complex, interacts with Cod1p, which regulates Ca²⁺ levels in the endoplasmic reticulum (ER), and with Rad4p, which is a nucleotide excision repair (NER) protein. This information was used to construct single and double mutants defective for Pmr1p, Cod1p, and Rad4p followed by cytotoxic, cytostatic, and cell cycle arrest analyses after cell exposure to different concentrations of 4-nitroquinoline 1-oxide (4-NQO). The results indicated that cod1Δ, cod1Δrad4Δ, and cod1Δpmr1Δ strains have an elevated sensitivity to 4-NQO when compared to its wild-type (WT) strain. Moreover, both cod1Δpmr1Δ and cod1Δrad4Δ strains have a strong arrest at G₂/M phases of cell cycle after 4-NQO treatment, while pmr1Δrad4Δ have a similar sensitivity and cell cycle arrest profile when compared to rad4Δ after 4-NQO exposure. Taken together, our results indicate that deletion in Golgi- and ER-associated Ca²⁺ transporters affect the repair of 4-NQO-induced DNA damage.     

Plant mitochondria use two pathways for the biogenesis of tRNAHis

All tRNA^His possess an essential extra G_–1 guanosine residue at their 5′ end. In eukaryotes after standard processing by RNase P, G_–1 is added by a tRNA^His guanylyl transferase. In prokaryotes, G_–1 is genome-encoded and retained during maturation. In plant mitochondria, although trnH genes possess a G_–1 we find here that both maturation pathways can be used. Indeed, tRNA^His with or without a G_–1 are found in a plant mitochondrial tRNA fraction. Furthermore, a recombinant Arabidopsis mitochondrial RNase P can cleave tRNA^His precursors at both positions G₊₁ and G_–1. The G_–1 is essential for recognition by plant mitochondrial histidyl-tRNA synthetase. Whether, as shown in prokaryotes and eukaryotes, the presence of uncharged tRNA^His without G_–1 has a function or not in plant mitochondrial gene regulation is an open question. We find that when a mutated version of a plant mitochondrial trnH gene containing no encoded extra G is introduced and expressed into isolated potato mitochondria, mature tRNA^His with a G_–1 are recovered. This shows that a previously unreported tRNA^His guanylyltransferase activity is present in plant mitochondria.