No abstract

We have reported on the capacity of (-)-epicatechin ((-)-EPI) to stimulate mitochondrial biogenesis (MiB) in mouse skeletal muscle (SkM). However, the mechanisms mediating the effects of (-)-EPI are not fully understood. We previously identified a role of the G-protein coupled estrogen receptor (GPER) in modulating the vascular effects of (-)-EPI. We therefore tested the hypothesis that GPER mediates (at least in part) the stimulatory effects of (-)-EPI on MiB in SkM cells. As an in vitro model, we employed mouse SkM-derived C2C12 myoblasts differentiated into myotubes. Using confocal microscopy, we detected GPER at the cell surface and cytoplasm in C2C12 myotubes. Treatment with (-)-EPI (3 and 10μM) resulted in the stimulation of MiB as per increases in mitochondrial inner (MitoTracker Red FM fluorescence staining) and outer membrane (porin protein levels) markers, transcription factors involved in MiB stimulation (i.e., nuclear respiratory factor-2 [NRF-2] and mitochondrial transcription factor A [TFAM] protein levels) and citrate synthase (CS) activity levels. (-)-EPI-treated myotubes were longer and wider compared to vehicle-treated myotubes. The effects of (-)-EPI on myotube mitochondria and cell size were larger in magnitude to those observed with the GPER agonist G-1. The chemical blockade and down-regulation (siRNA) of GPER evidenced a partial and complete blockade of measured endpoints following (-)-EPI- or G-1-treatment, respectively. Altogether, results indicate that GPER is expressed in muscle cells and appears to mediate to a significant extent, the stimulatory effects of (-)-EPI on MiB. Thus, GPER activation may account for the stimulatory effects of (-)-EPI on SkM structure/function.

Anti-lipid IgG antibodies are produced in some mycobacterial infections and in certain autoimmune diseases [such as anti-phospholipid syndrome, systemic lupus erythematosus (SLE)]. However, few studies have addressed the B cell responses underlying the production of these immunoglobulins. Anti-lipid IgG antibodies are consistently found in a murine model resembling human lupus induced by chlorpromazine-stabilized non-bilayer phospholipid arrangements (NPA). NPA are transitory lipid associations found in the membranes of most cells; when NPA are stabilized they can become immunogenic and induce specific IgG antibodies, which appear to be involved in the development of the mouse model of lupus. Of note, anti-NPA antibodies are also detected in patients with SLE and leprosy. We used this model of lupus to investigate in vivo the cellular mechanisms that lead to the production of anti-lipid, class-switched IgG antibodies. In this murine lupus model, we found plasma cells (Gr1−, CD19−, CD138+) producing NPA-specific IgGs in the draining lymph nodes, the spleen, and the bone marrow. We also found a significant number of germinal center B cells (IgD−, CD19+, PNA+) specific for NPA in the draining lymph nodes and the spleen, and we identified in situ the presence of NPA in these germinal centers. By contrast, very few NPA-specific, extrafollicular reaction B cells (B220+, Blimp1+) were found. Moreover, when assessing the anti-NPA IgG antibodies produced during the experimental protocol, we found that the affinity of these antibodies progressively increased over time. Altogether, our data indicate that, in this murine model resembling human lupus, B cells produce anti-NPA IgG antibodies mainly via germinal centers.

Estrogens demonstrate biological activity in numerous organ systems, including the immune system, and exert their effects through estrogen receptors (ER) of two types: intracellular ERα and ERβ that activate transcriptional factors and membrane G protein‐coupled ER GPER. The latter is capable to mediate fast activation of cytosolic signaling pathways, influencing transcriptional events in response to estrogens. Tamoxifen (TAM), widely used in chemotherapy of ERα‐positive breast cancer, is considered as an ERα antagonist and GPER agonist. TAM was shown to possess “off‐target” cytotoxicity, not related to ER in various tumor types. The present work was designed to study biological effects of TAM on the glucocorticoid (GC)‐resistant cell line Jurkat, derived from acute lymphoblastic leukemia of T lineage (T‐ALL). We have shown that T‐ALL cell lines, in contrast to healthy T cells, express only GPER, but not ERα or ERβ. TAM compromised mitochondrial function and reduced the viability and proliferation of Jurkat cells. Additionally, TAM induced autophagy in a GPER‐dependent manner. Gene expression profiling revealed the up‐regulation of autophagy‐related gene ATG5. Interestingly, TAM sensitized Jurkat cells to dexamethasone (DEX) treatment, which may be related to its capacity to cause autophagy. We suggest that TAM‐based adjuvant therapy may represent a novel strategy in T‐ALL patients handling.