Myristoylated, alanine-rich C-kinase substrate (MARCKS) regulates toll-like receptor 4 signaling in macrophages

Natural phytochemicals reverting M2 to M1 macrophages: A novel alternative leishmaniasis therapy

INTRODUCTION

Leishmaniasis is a tropical parasitic disease caused by the protozoan Leishmania which remains a significant global health concern with diverse clinical manifestations. Transmitted through the bite of an infected sandfly, its progression depends on the interplay between the host immune response and the parasite. The disease outcome is linked to macrophage polarisation into M1 and M2 phenotypes. M1 macrophages are pro-inflammatory and promote parasite clearance, while M2 macrophages support tissue repair and parasite survival by facilitating promastigote entry and intracellular amastigote proliferation.

PURPOSE

The review focuses on discovering novel phytochemicals that exploit the immunomodulatory properties of macrophages, which can serve as an alternative antileishmanial treatments due to their diverse chemical structures and ability to modulate immune responses. It examines the immunomodulatory effects of phytochemicals that directly or indirectly promote antileishmanial activity by influencing macrophage polarisation and cytokine secretion. They can induce M1 macrophage polarisation to directly combat leishmaniasis or suppress M2 macrophages, thereby exerting indirect antileishmanial activity by influencing the release of M1-and M2-related cytokines.

RESULTS & DISCUSSION

Phytochemicals demonstrate antileishmanial effects through ROS production, M1 activation, and cytokine modulation. They regulate M1/M2-related cytokines and macrophage activity, influencing immune responses. Although their effects may be non-specific, targeted delivery strategies could overcome current therapeutic limitations, positioning phytochemicals as promising candidates for leishmaniasis treatment to counter the limitations of current medications.

Lipopolysaccharide Regulates the Macrophage RNA-Binding Proteome

RNA-protein interactions within cellular signaling pathways have significant modulatory effects on RNA binding proteins' (RBPs') effector functions. During the innate immune response, specific RNA-protein interactions have been reported as a regulatory layer of post-transcriptional control. We investigated changes in the RNA-bound proteome of immortalized mouse macrophages (IMM) following treatment with lipopolysaccharide (LPS). Stable isotope labeling by amino acids in cell culture (SILAC) of cells followed by unbiased purification of RNP complexes at two time points after LPS stimulation and bottom-up proteomic analysis by LC-MS/MS resulted in a set of significantly affected RBPs. Global RNA sequencing and LFQ proteomics were used to characterize the correlation of transcript and protein abundance changes in response to LPS at different time points with changes in protein-RNA binding. Il1α, MARCKS, and ACOD1 were noted as RBP candidates involved in innate immune signaling. The binding sites of the RBP and RNA conjugates at amino acid resolution were investigated by digesting the cross-linked oligonucleotide from peptides remaining after elution using Nuclease P1. The combined data sets provide directions for further studies of innate immune signaling regulation by RBP interactions with different classes of RNA.

Comparative gene regulatory networks modulating APOE expression in microglia and astrocytes

Background

Single-cell technologies have unveiled various transcriptional states in different brain cell types. Transcription factors (TFs) regulate the expression of related gene sets, thereby controlling these diverse expression states. Apolipoprotein E (APOE), a pivotal risk-modifying gene in Alzheimer's disease (AD), is expressed in specific glial transcriptional states associated with AD. However, it is still unknown whether the upstream regulatory programs that modulate its expression are shared across brain cell types or specific to microglia and astrocytes.

Methods

We used pySCENIC to construct state-specific gene regulatory networks (GRNs) for resting and activated cell states within microglia and astrocytes based on single-nucleus RNA sequencing data from AD patients' cortices from the Knight ADRC-DIAN cohort. We then identified replicating TF using data from the ROSMAP cohort. We identified sets of genes co-regulated with APOE by clustering the GRN target genes and identifying genes differentially expressed after the virtual knockout of TFs regulating APOE. We performed enrichment analyses on these gene sets and evaluated their overlap with genes found in AD GWAS loci.

Results

We identified an average of 96 replicating regulators for each microglial and astrocyte cell state. Our analysis identified the CEBP, JUN, FOS, and FOXO TF families as key regulators of microglial APOE expression. The steroid/thyroid hormone receptor families, including the THR TF family, consistently regulated APOE across astrocyte states, while CEBP and JUN TF families were also involved in resting astrocytes. AD GWAS-associated genes (PGRN, FCGR3A, CTSH, ABCA1, MARCKS, CTSB, SQSTM1, TSC22D4, FCER1G, and HLA genes) are co-regulated with APOE. We also uncovered that APOE-regulating TFs were linked to circadian rhythm (BHLHE40, DBP, XBP1, CREM, SREBF1, FOXO3, and NR2F1).

Conclusions

Our findings reveal a novel perspective on the transcriptional regulation of APOE in the human brain. We found a comprehensive and cell-type-specific regulatory landscape for APOE, revealing distinct and shared regulatory mechanisms across microglia and astrocytes, underscoring the complexity of APOE regulation. APOE-co-regulated genes might also affect AD risk. Furthermore, our study uncovers a potential link between circadian rhythm disruption and APOE regulation, shedding new light on the pathogenesis of AD.