HuR promotes the molecular signature and phenotype of activated microglia: Implications for amyotrophic lateral sclerosis and other neurodegenerative diseases

In neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), chronic activation of microglia contributes to disease progression. Activated microglia produce cytokines, chemokines, and other factors that normally serve to clear infection or damaged tissue either directly or through the recruitment of other immune cells. The molecular program driving this phenotype is classically linked to the transcription factor NF-κB and characterized by the upregulation of proinflammatory factors such as IL-1β, TNF-α, and IL-6. Here, we investigated the role of HuR, an RNA-binding protein that regulates gene expression through posttranscriptional pathways, on the molecular and cellular phenotypes of activated microglia. We performed RNA sequencing of HuR-silenced microglia and found significant attenuation of lipopolysaccharide-induced IL-1β and TNF-α inflammatory pathways and other factors that promote microglial migration and invasion. RNA kinetics and luciferase reporter studies suggested that the attenuation was related to altered promoter activity rather than a change in RNA stability. HuR-silenced microglia showed reduced migration, invasion, and chemotactic properties but maintained viability. MMP-12, a target exquisitely sensitive to HuR knockdown, participates in the migration/invasion phenotype. HuR is abundantly detected in the cytoplasmic compartment of activated microglia from ALS spinal cords consistent with its increased activity. Microglia from ALS-associated mutant SOD1 mice demonstrated higher migration/invasion properties which can be blocked with HuR inhibition. These findings underscore an important role for HuR in sculpting the molecular signature and phenotype of activated microglia, and as a possible therapeutic target in ALS and other neurodegenerative diseases.

A gene expression analysis of syncytia laser microdissected from the roots of the Glycine max (soybean) genotype PI 548402 (Peking) undergoing a resistant reaction after infection by Heterodera glycines (soybean cyst nematode)

The syncytium is a nurse cell formed within the roots of Glycine max by the plant parasitic nematode Heterodera glycines. Its development and maintenance are essential for nematode survival. The syncytium appears to undergo two developmental phases during its maturation into a functional nurse cell. The first phase is a parasitism phase where the nematode establishes the molecular circuitry that during the second phase ensures a compatible interaction with the plant cell. The cytological features of syncytia undergoing susceptible or resistant reactions appear the same during the parasitism phase. Depending on the outcome of any defense response, the second phase is a period of syncytium maintenance (susceptible reaction) or failure (resistant reaction). In the analyses presented here, the localized gene expression occurring at the syncytium during the resistant reaction was studied. This was accomplished by isolating syncytial cells from Glycine max genotype Peking (PI 548402) by laser capture microdissection. Microarray analyses using the Affymetrix soybean GeneChip directly compared Peking syncytia undergoing a resistant reaction to those undergoing a susceptible reaction during the parasitism phase of the resistant reaction. Those analyses revealed lipoxygenase-9 and lipoxygenase-4 as the most highly induced genes in the resistant reaction. The analysis also identified induced levels of components of the phenylpropanoid pathway. These genes included phenylalanine ammonia lyase, chalcone isomerase, isoflavone reductase, cinnamoyl-CoA reductase and caffeic acid O-methyltransferase. The presence of induced levels of these genes implies the importance of jasmonic acid and phenylpropanoid signaling pathways locally at the site of the syncytium during the resistance phase of the resistant reaction. The analysis also identified highly induced levels of four S-adenosylmethionine synthetase genes, the EARLY-RESPONSIVE TO DEHYDRATION 2 gene and the 14-3-3 gene known as GENERAL REGULATORY FACTOR 2. Subsequent analyses studied microdissected syncytial cells at 3, 6 and 9 days post infection (dpi) during the course of the resistant reaction, resulting in the identification of signature gene expression profiles at each time point in a single G. max genotype, Peking.