Nicolas J. Pillon

Different immune cells mediate mechanical pain hypersensitivity in male and female mice

A large and rapidly increasing body of evidence indicates that microglia-to-neuron signaling is essential for chronic pain hypersensitivity. Using multiple approaches, we found that microglia are not required for mechanical pain hypersensitivity in female mice; female mice achieved similar levels of pain hypersensitivity using adaptive immune cells, likely T lymphocytes. This sexual dimorphism suggests that male mice cannot be used as proxies for females in pain research.

Cross-talk between skeletal muscle and immune cells: muscle-derived mediators and metabolic implications

Skeletal muscles contain resident immune cell populations and their abundance and type is altered in inflammatory myopathies, endotoxemia or different types of muscle injury/insult. Within tissues, monocytes differentiate into macrophages and polarize to acquire pro- or anti-inflammatory phenotypes. Skeletal muscle macrophages play a fundamental role in repair and pathogen clearance. These events require a precisely regulated cross-talk between myofibers and immune cells, involving paracrine/autocrine and contact interactions. Skeletal muscle also undergoes continuous repair as a result of contractile activity that involves participation of myokines and anti-inflammatory input. Finally, skeletal muscle is the major site of dietary glucose disposal; therefore, muscle insulin resistance is essential to the development of whole body insulin resistance. Notably, muscle inflammation is emerging as a potential contributor to insulin resistance. Recent reports show that inflammatory macrophage numbers within muscle are elevated during obesity and that muscle cells in vitro can mount autonomous inflammatory responses under metabolic challenge. Here, we review the nature of skeletal muscle inflammation associated with muscle exercise, damage, and regeneration, endotoxin presence, and myopathies, as well as the new evidence of local inflammation arising with obesity that potentially contributes to insulin resistance.

Muscle cells challenged with saturated fatty acids mount an autonomous inflammatory response that activates macrophages

Obesity is associated with chronic low-grade inflammation. Within adipose tissue of mice fed a high fat diet, resident and infiltrating macrophages assume a pro-inflammatory phenotype characterized by the production of cytokines which in turn impact on the surrounding tissue. However, inflammation is not restricted to adipose tissue and high fat-feeding is responsible for a significant increase in pro-inflammatory cytokine expression in muscle. Although skeletal muscle is the major disposer of dietary glucose and a major determinant of glycemia, the origin and consequence of muscle inflammation in the development of insulin resistance are poorly understood.We used a cell culture approach to investigate the vectorial crosstalk between muscle cells and macrophages upon exposure to physiological, low levels of saturated and unsaturated fatty acids. Inflammatory pathway activation and cytokine expression were analyzed in L6 muscle cells expressing myc-tagged GLUT4 (L6GLUT4myc) exposed to 0.2 mM palmitate or palmitoleate. Conditioned media thereof, free of fatty acids, were then tested for their ability to activate RAW264.7 macrophages.Palmitate -but not palmitoleate- induced IL-6, TNFα and CCL2 expression in muscle cells, through activation of the NF-κB pathway. Palmitate (0.2 mM) alone did not induce insulin resistance in muscle cells, yet conditioned media from palmitate-challenged muscle cells selectively activated macrophages towards a pro-inflammatory phenotype.These results demonstrate that low concentrations of palmitate activate autonomous inflammation in muscle cells to release factors that turn macrophages pro-inflammatory. We hypothesize that saturated fat-induced, low-grade muscle cell inflammation may trigger resident skeletal muscle macrophage polarization, possibly contributing to insulin resistance in vivo.

Innate immune receptors in skeletal muscle metabolism

ABSTRACT Recent decades have seen increasing evidence for a role for both innate and adaptive immunity in response to changes in and in the modulation of metabolic status. This new field of immunometabolism builds on evidence for activation of immune‐derived signals in metabolically relevant tissues such as adipose tissue, liver, hypothalamus and skeletal muscle. Skeletal muscle is the primary site of dietary glucose disposal and therefore a key player in the development of diabetes, but studies on the role of inflammation in modulating skeletal muscle metabolism and its possible impact on whole body insulin sensitivity are scarce. This review describes the baseline mRNA expression of innate immune receptors (Toll‐ and NOD‐like receptors) in human skeletal muscle and summarizes studies on putative role of these receptors in skeletal muscle in the context of diabetes, obesity and whole body metabolism.

Circadian Rhythms and Mitochondria: Connecting the Dots

Circadian rhythms provide a selective advantage by anticipating organismal nutrient needs and guaranteeing optimal metabolic capacity during active hours. Impairment of circadian rhythms is associated with increased risk of type 2 diabetes and emerging evidence suggests that metabolic diseases are linked to perturbed clock machinery. The circadian clock regulates many transcriptional–translational processes influencing whole cell metabolism and particularly mitochondrial activity. In this review, we survey the current literature related to cross-talks between mitochondria and the circadian clock and unravel putative molecular links. Understanding the mechanisms that link metabolism and circadian responses to transcriptional modifications will provide valuable insights toward innovative therapeutic strategies to combat the development of metabolic disease.

IL6 and LIF mRNA expression in skeletal muscle is regulated by AMPK and the transcription factors NFYC, ZBTB14 and SP1

Adenosine monophosphate-activated protein kinase (AMPK) controls glucose and lipid metabolism and modulates inflammatory responses to maintain metabolic and inflammatory homeostasis during low cellular energy levels. The AMPK activator 5-aminoimidazole-4-carboxamide-1-β-4-ribofuranoside (AICAR) interferes with inflammatory pathways in skeletal muscle, but the mechanisms are undefined. We hypothesized that AMPK activation reduces cytokine mRNA levels by blocking transcription through one or several transcription factors. Three skeletal muscle models were used to study AMPK effects on cytokine mRNA: human skeletal muscle strips obtained from healthy men incubated in vitro, primary human muscle cells, and rat L6 cells. In all three skeletal muscle systems, AICAR acutely reduced cytokine mRNA levels. In L6 myotubes treated with the transcriptional blocker actinomycin D, AICAR addition did not further reduce Il6 or leukemia inhibitory factor ( Lif) mRNA, suggesting that AICAR modulates cytokine expression through regulating transcription rather than mRNA stability. A cross-species bioinformatic approach identified novel transcription factors that may regulate LIF and IL6 mRNA. The involvement of these transcription factors was studied after targeted gene-silencing by siRNA. siRNA silencing of the transcription factors nuclear transcription factor Y subunit c ( Nfyc), specificity protein 1 ( Sp1), and zinc finger and BTB domain containing 14 ( Zbtb14), or AMPK α1/α2 subunits, increased constitutive levels of Il6 and Lif. Our results identify novel candidates in the regulation of skeletal muscle cytokine expression and identify AMPK, Nfyc, Sp1, and Zbtb14 as novel regulators of immunometabolic signals from skeletal muscle.