Rapid and Direct Action of Lipopolysaccharide (LPS) on Skeletal Muscle of Larval Drosophila

LncRNA TUG1 relieves renal mesangial cell injury by modulating the miR-153-3p/Bcl-2 axis in lupus nephritis

BACKGROUND

Lupus nephritis (LN) is one of the most common and serious complications of systemic lupus erythematosus. Our experiments aimed to evaluate the molecular mechanisms of long noncoding RNA (lncRNA) TUG1 in a human renal mesangial cell (HRMC) model of LN.

METHODS

Cells were treated with lipopolysaccharide (LPS) to induce inflammatory damage. StarBase, TargetScan, and a luciferase reporter assay were used to predict and confirm the interactions between lncRNA TUG1, miR-153-3p, and Bcl-2. We determined the lncRNA TUG1 and miR-153-3p levels in LPS-induced HRMCs using quantitative reverse transcription PCR (RT-qPCR). MTT and flow cytometry analyses were used to detect HRMC proliferation and apoptosis, respectively. In addition, the expression of the apoptosis-related proteins Bax and Bcl-2 was evaluated using western blot analysis and RT-qPCR. Lastly, the secretion of inflammatory cytokines (IL-1β, IL-6, and TNF-α) was assessed using ELISA.

RESULTS

miR-153-3p directly targeted lncRNA TUG1. The level of lncRNA TUG1 was remarkably lower and miR-153-3p expression was markedly higher in LPS-treated HRMCs than in untreated cells. Transfection with TUG1-plasmid relieved LPS-induced HRMC injury, as evidenced by increased cell viability, inhibited apoptotic cells, reduced Bax expression, increased Bcl-2 level, and reduced secretion of inflammatory cytokines. Importantly, these findings were reversed by miR-153-3p mimic. We also found that miR-153-3p directly targeted Bcl-2 and negatively regulated Bcl-2 expression in HRMCs. In addition, our findings suggest that miR-153-3p inhibitor relieved LPS-induced HRMC injury via the upregulation of Bcl-2.

CONCLUSION

lncRNA TUG1 alleviated LPS-induced HRMC injury through regulation of the miR-153-3p/Bcl-2 axis in LN.

The effects of doxapram (blocker of K2p channels) on resting membrane potential and synaptic transmission at the Drosophila neuromuscular junction

The resting membrane potential of most cells is maintained by potassium K2p channels. The pharmacological profile and distribution of various K2p channel subtypes in organisms are still being investigated. The Drosophila genome contains 11 subtypes; however, their function and expression profiles have not yet been determined. Doxapram is clinically used to enhance respiration in humans and blocks the acid-sensitive K2p TASK subtype in mammals. The resting membrane potential of larval Drosophila muscle and synaptic transmission at the neuromuscular junction are pH sensitive. The present study investigated the effects of doxapram on membrane potential and synaptic transmission using intracellular recordings of larval Drosophila muscles. Doxapram (1 mM and 10 mM) depolarizes the muscle and appears to depolarize motor neurons, causing an increase in the frequency of spontaneous quantal events and evoked excitatory junction potentials. Verapamil (1 and 10 mM) paralleled the action of doxapram. These changes were matched by an extracellular increase in KCl (50 mM) and blocked by Cd²⁺. It is assumed that the motor nerve depolarizes to open voltage-gated Ca²⁺ channels in presynaptic nerve terminals because of exposure to doxapram. These findings are significant for building models to better understand the function of pharmacological agents that affect K2p channels and how K2p channels contribute to the physiology of tissues. Drosophila offers a genetically amenable model that can alter the tissue-specific expression of K2p channel subtypes to simulate known human diseases related to this family of channels.

Hyperpolarization Induced by Lipopolysaccharides but Not by Chloroform Is Inhibited by Doxapram, an Inhibitor of Two-P-Domain K+ Channel (K2P)

Bacterial septicemia is commonly induced by Gram-negative bacteria. The immune response is triggered in part by the secretion of bacterial endotoxin lipopolysaccharide (LPS). LPS induces the subsequent release of inflammatory cytokines which can result in pathological conditions. There is no known blocker to the receptors of LPS. The Drosophila larval muscle is an amendable model to rapidly screen various compounds that affect membrane potential and synaptic transmission such as LPS. LPS induces a rapid hyperpolarization in the body wall muscles and depolarization of motor neurons. These actions are blocked by the compound doxapram (10 mM), which is known to inhibit a subtype of the two-P-domain K+ channel (K2P channels). However, the K2P channel blocker PK-THPP had no effect on the Drosophila larval muscle at 1 and 10 mM. These channels are activated by chloroform, which also induces a rapid hyperpolarization of these muscles, but the channels are not blocked by doxapram. Likewise, chloroform does not block the depolarization induced by doxapram. LPS blocks the postsynaptic glutamate receptors on Drosophila muscle. Pre-exposure to doxapram reduces the LPS block of these ionotropic glutamate receptors. Given that the larval Drosophila body wall muscles are depolarized by doxapram and hyperpolarized by chloroform, they offer a model to begin pharmacological profiling of the K2P subtype channels with the potential of identifying blockers for the receptors to mitigate the actions of the Gram-negative endotoxin LPS.

Mutations of γCOP Gene Disturb Drosophila melanogaster Innate Immune Response to Pseudomonas aeruginosa

Drosophila melanogaster (the fruit fly) is a valuable experimental platform for modeling host–pathogen interactions. It is also commonly used to define innate immunity pathways and to understand the mechanisms of both host tolerance to commensal microbiota and response to pathogenic agents. Herein, we investigate how the host response to bacterial infection is mirrored in the expression of genes of Imd and Toll pathways when D. melanogaster strains with different γCOP genetic backgrounds are infected with Pseudomonas aeruginosa ATCC 27853. Using microarray technology, we have interrogated the whole-body transcriptome of infected versus uninfected fruit fly males with three specific genotypes, namely wild-type Oregon, γCOP^S057302/TM6B and γCOP^14a/γCOP^14a. While the expression of genes pertaining to Imd and Toll is not significantly modulated by P. aeruginosa infection in Oregon males, many of the components of these cascades are up- or downregulated in both infected and uninfected γCOP^S057302/TM6B and γCOP^14a/γCOP^14a males. Thus, our results suggest that a γCOP genetic background modulates the gene expression profiles of Imd and Toll cascades involved in the innate immune response of D. melanogaster, inducing the occurrence of immunological dysfunctions in γCOP mutants.