Quenching of endogenous peroxidase in western blot

Inactivation of horseradish peroxidase with crotonic acid for reprobing of western blotting

Inactivation of horseradish peroxidase (HRP) treatment is a conventional preference to stripping for sequential detections of different proteins of chemiluminescent western blotting (WB). However, little evidence exists on whether other chemical substances treatment can affects the biological activity of HRP during stripping and re-probing of WB blots. Here, we successfully develop 20% crotonic acid (CA) as an alternative to stripping to inhibit HRP used for sequential chemiluminescent WB on polyvinylidene difluoride (PVDF) and Nitrocellulose (NC) membrane. Moreover, NC blots incubation in CA (40 °C, 30min) allow us to perform three round HRP inhibition in sequential detections without losing transferred proteins and damaging membrane. Hence, the method will help us save time and valuable samples without the need to rerun gels.

Crosstalk of hepatocyte nuclear factor 4a and glucocorticoid receptor in the regulation of lipid metabolism in mice fed a high-fat-high-sugar diet

Background

Hepatocyte nuclear factor 4α (HNF4α) and glucocorticoid receptor (GR), master regulators of liver metabolism, are down-regulated in fatty liver diseases. The present study aimed to elucidate the role of down-regulation of HNF4α and GR in fatty liver and hyperlipidemia.

Methods

Adult mice with liver-specific heterozygote (HET) and knockout (KO) of HNF4α or GR were fed a high-fat-high-sugar diet (HFHS) for 15 days. Alterations in hepatic and circulating lipids were determined with analytical kits, and changes in hepatic mRNA and protein expression in these mice were quantified by real-time PCR and Western blotting. Serum and hepatic levels of bile acids were quantified by LC-MS/MS. The roles of HNF4α and GR in regulating hepatic gene expression were determined using luciferase reporter assays.

Results

Compared to HFHS-fed wildtype mice, HNF4α HET mice had down-regulation of lipid catabolic genes, induction of lipogenic genes, and increased hepatic and blood levels of lipids, whereas HNF4α KO mice had fatty liver but mild hypolipidemia, down-regulation of lipid-efflux genes, and induction of genes for uptake, synthesis, and storage of lipids. Serum levels of chenodeoxycholic acid and deoxycholic acid tended to be decreased in the HNF4α HET mice but dramatically increased in the HNF4α KO mice, which was associated with marked down-regulation of cytochrome P450 7a1, the rate-limiting enzyme for bile acid synthesis. Hepatic mRNA and protein expression of sterol-regulatory-element-binding protein-1 (SREBP-1), a master lipogenic regulator, was induced in HFHS-fed HNF4α HET mice. In reporter assays, HNF4α cooperated with the corepressor small heterodimer partner to potently inhibit the transactivation of mouse and human SREBP-1C promoter by liver X receptor. Hepatic nuclear GR proteins tended to be decreased in the HNF4α KO mice. HFHS-fed mice with liver-specific KO of GR had increased hepatic lipids and induction of SREBP-1C and PPARγ, which was associated with a marked decrease in hepatic levels of HNF4α proteins in these mice. In reporter assays, GR and HNF4α synergistically/additively induced lipid catabolic genes.

Conclusions

induction of lipid catabolic genes and suppression of lipogenic genes by HNF4α and GR may mediate the early resistance to HFHS-induced fatty liver and hyperlipidemia.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-022-01654-6.

Multiple reprobing of Western blots after inactivation of peroxidase activity by its substrate, hydrogen peroxide

Sequential detections of different proteins on Western blot save time and precious samples. The main problem concerning reprobing is that stripping buffers can unbind both the antibody and the tested antigen. An original reprobing method has been set up based on horseradish peroxidase (HRP) inhibition after enhanced chemiluminescence detection. Instead of removing previously fixed antibodies as common stripping buffers do, the HRP activity linked to the secondary antibody is irreversibly inhibited by excess of hydrogen peroxide. A 15-min incubation allows one to perform at least five different sequential detections without losing significant amounts of blotted proteins.

Ca2+/calmodulin-dependent protein kinase II isoenzymes gamma and delta are both present in H+/K+-ATPase-containing rabbit gastric tubulovesicles

Ca2+/calmodulin-dependent protein kinase II is thought to participate in M3 muscarinic receptor-mediated acid secretion in gastric parietal cells. During acid secretion tubulovesicles carrying H+/K+-ATPase fuse with the apical membrane. We localized Ca2+/calmodulin-dependent protein kinase II from highly purified rabbit gastric tubulovesicles using Ca2+/calmodulin-dependent protein kinase II isoform-specific antibodies, in vitro phosphorylation and pharmacological inhibition of Ca2+/calmodulin-dependent protein kinase II activity by the potent Ca2+/calmodulin-dependent protein kinase II inhibitor KN-62. The presence of Ca2+/calmodulin-dependent protein kinase II in tubulovesicles was shown by immunoblot detection of both Ca2+/calmodulin-dependent protein kinase II-gamma (54 kDa) and Ca2+/calmodulin-dependent protein kinase II-delta (56.5 kDa). The immunoprecipitated Ca2+/calmodulin-dependent protein kinase II from tubulovesicles showed Ca2+/calmodulin-dependent protein kinase activity by phosphorylating autocamtide-II, a specific synthetic Ca2+/calmodulin-dependent protein kinase II substrate. KN-62 inhibited the in vitro autophosphorylation of tubulovesicle-associated Ca2+/calmodulin-dependent protein kinase II (IC50 = 11 nM). During the search for potential Ca2+/calmodulin-dependent protein kinase II substrates we identified different proteins associated with tubulovesicles, such as synaptophysin and beta-tubulin immunoreactivity, which were identified using specific antibodies. These targets are known to participate in intracellular membrane traffic. Ca2+/calmodulin-dependent protein kinase II is thought to play an important role in regulating tubulovesicular motor activity and therefore in acid secretion.

The protective effects of zinc on diethyldithiocarbamate cytotoxicity on rat astrocytes in vitro

The neurotoxicity of diethyldithiocarbamate (DDC) has been documented for decades. In particular, cytotoxic effects against rat astrocytes have been noted by a decrease in cell viability and numerous ultrastructural defects. This study indicates an in vitro protective effect by zinc administration prior to DDC insult. Cell groups pre-treated with 50 microM ZnCl2 prior to the addition of 35 microg/ml DDC showed significant protection when compared with cells treated with DDC alone. Zinc reduced the DDC-mediated toxicity to astrocytes as indicated by an increase in cell adherence and viability. Morphological evaluation indicated a significant decrease in ultrastructural alterations. Metallothionein (MT), a metal regulatory protein known to be induced by zinc was studied to determine its role in this mechanism of protection. Immunocytochemistry and immunoblots showed increased presence of MT in all zinc treated groups. This suggests a protective effect against DDC cytotoxicity on rat astrocytes in vitro may be associated with an increase in MT concentration.

Isolation and characterization of 26- and 30-kDa rat liver proteins immunoreactive to anti-sterol carrier protein-2 antibodies

Although the existing literature suggests that the sterol carrier protein-2 (SCP-2) gene has only two initiation sites encoding for a 58- and a 15-kDa protein, respectively, this does not explain the profusion of other putative SCP-2-related proteins detectable on Western blotting. Two of these additional anti-SCP-2 immunoreactive proteins, 13.2 and 46 kDa, appear due to proteolytic processing of the two gene transcripts. However, the origin of additional immunoreactive rat liver proteins near 26 and 30 kDa is unclear. The latter proteins were consistently detected on Western blotting by three independent types of polyclonal antisera: anti-13.2-kDa SCP-2, anti-synthetic peptide from the amino-terminus of the 13.2-kDa SCP-2, and Protein A affinity-purified anti-synthetic peptide to the amino-terminus of 13.2-kDa SCP-2. To resolve whether the 26- and 30-kDa proteins are SCP-2 gene products, each protein was isolated from rat liver and purified to homogeneity as indicated by Tricine-SDS polyacrylamide gel electrophoresis, isoelectric focusing, and/or mass spectroscopy. Their masses, determined by MALDI-TOF mass spectroscopy, were 25.7 and 29.8 kDa, respectively. However, the mass spectral data were not consistent with either protein being an SCP-2 gene product. Peptide mass mapping of the 25.7-kDa protein revealed identity to the rat 25,784.79-Da glutathione-S-transferase. Furthermore, neither the mass nor the amino acid composition of the 29.8-kDa protein correlated with any SCP-2 gene product or dimerized SCP-2 gene product. A database search of the amino acid composition identified the protein as rat carbonic anhydrase. In summary, although the 26- and 29.8-kDa proteins may share some common epitopes with the 13.2-kDa SCP-2, they were not SCP-2 gene products.