Previous results showed that intermittently administered Irisin improves bone mass in normal mice and prevents the development of disuse‐induced osteoporosis and muscular atrophy in hind‐limb suspended mice, a murine model able to mimic the absence of mechanical loading. A recent study showed that Irisin increases survival of osteocytes acting through integrin αV/β5 receptors. To better understand the action of Irisin on these cells, we investigated the downstream signaling cascades in osteocyte‐like cells (MLO‐Y4) treated with recombinant Irisin (rec‐Irisin) in vitro and we analyzed survival of osteocytes and caspase activation in cortical bone of osteoporotic mice treated with rec‐Irisin in vivo. Our results revealed that rec‐Irisin activated the MAP kinases Erk1‐2 and increased the expression of the transcription factor Atf4 (2.5‐fold, p<0.05) through an Erk‐dependent pathway in osteocytes. Some key genes expressed by MLO‐Y4 cells were modulated by long term Irisin treatment, either continuously administered or given with intermittent short pulses. Interestingly, Sost mRNA was severely downregulated only upon intermittent Irisin administration (10‐fold, p<0.001). Furthermore, rec‐Irisin upregulated Tfam mRNA (4‐fold, p<0.05) and Bcl2/Bax ratio (2‐fold, p<0.05) in MLO‐Y4 cells. By detecting Caspase‐9 and Caspase‐3, we also found that rec‐Irisin inhibited apoptosis induced by hydrogen peroxide and dexamethasone, respectively. In cortical bone of unloading C57BL6 mice, Irisin prevented disuse‐induced reduction of viable osteocytes (+30% Vs unload‐veh, p<0.05) and increase of empty lacunae (+110% Vs unload‐veh, p<0.05), as well as Caspase‐9 (3‐fold, p<0.05) and Caspase‐3 (2‐fold, p<0.05) activations. Our findings revealed underlying mechanisms of Irisin action on osteocytes, which increases their functions and exerts anti‐apoptotic effects, confirming that mechanosensor cells of bone are sensitive to the exercise‐mimetic myokine Irisin.

Gliomas, particularly glioblastoma multiforme, perturb the blood-brain barrier and cause brain edema that contributes to morbidity and mortality. The

P-Glycoprotein (P-gp) is an ATP-dependent efflux transporter that extrudes non-polar molecules, including cytotoxic substances and drugs, from the cells. It was initially found in cancer cells and then was shown to be a normal component of complex transport systems working at the blood-brain barrier (BBB). Previous studies have demonstrated that, in the brain, P-gp is localized on the luminal plasmalemma of BBB endothelial cells and that it may interact with the caveolar compartment of these cells. The aim of this study was to identify the site of cellular expression of P-gp in human brain in situ and to morphologically determine whether an association may exist between P-gp and caveolin-1, a structural and functional protein of the caveolar frame. The study was carried out on human cerebral cortex by immunoconfocal microscopy with antibodies to both P-gp and caveolin-1. The results show that P-gp marks the microvessels of the cortex and that the transporter is localized in the luminal endothelial compartment, where it co-localizes with caveolin-1. The demonstration of this co-localization of P-gp with caveolin-1 contributes a morphological backing to biochemical studies on P-gp/caveolin-1 relationships and leads us to suggest that interactions between these molecules may occur at the BBB endothelia.