Circulating ghrelin crosses the blood-cerebrospinal fluid barrier via growth hormone secretagogue receptor dependent and independent mechanisms

Ghrelin is a peptide hormone mainly secreted from gastrointestinal tract that acts via the growth hormone secretagogue receptor (GHSR), which is highly expressed in the brain. Strikingly, the accessibility of ghrelin to the brain seems to be limited and restricted to few brain areas. Previous studies in mice have shown that ghrelin can access the brain via the blood-cerebrospinal fluid (CSF) barrier, an interface constituted by the choroid plexus and the hypothalamic tanycytes. Here, we performed a variety of in vivo and in vitro studies to test the hypothesis that the transport of ghrelin across the blood-CSF barrier occurs in a GHSR-dependent manner. In vivo, we found that the uptake of systemically administered fluorescent ghrelin in the choroid plexus epithelial (CPE) cells and in hypothalamic tanycytes depends on the presence of GHSR. Also, we detected lower levels of CSF ghrelin after a systemic ghrelin injection in GHSR-deficient mice, as compared to WT mice. In vitro, the internalization of fluorescent ghrelin was reduced in explants of choroid plexus from GHSR-deficient mice, and unaffected in primary cultures of hypothalamic tanycytes derived from GHSR-deficient mice. Finally, we found that the GHSR mRNA is detected in a pool of CPE cells, but is nearly undetectable in hypothalamic tanycytes with current approaches. Thus, our results suggest that circulating ghrelin crosses the blood-CSF barrier mainly by a mechanism that involves the GHSR, and also possibly via a GHSR-independent mechanism.

A role for the putative cannabinoid receptor GPR55 in the islets of Langerhans

The cannabinoid CB1 receptor is a well-known player in energy homeostasis and its specific antagonism has been used in clinical practice for the treatment of obesity. The G protein-coupled receptor GPR55 has been recently proposed as a new cannabinoid receptor and, by contrast, its pharmacology is still enigmatic and its physiological role is largely unexplored, with no reports investigating its putative role in metabolism. Thus, we aim to investigate in rats the presence, distribution and putative physiological role of GPR55 in a key metabolic tissue, the endocrine pancreas. We found high Gpr55 mRNA content in pancreatic islets and considerable protein distribution in insulin-secreting β-cells. Activation of GPR55 by the agonist O-1602 increased calcium transients (P<0.01) and insulin secretion (P<0.001) stimulated by glucose. This latter effect was blunted in Gpr55 KO mice suggesting that O-1602 is acting, at least in part, through GPR55. Indeed, acute in vivo experiments showed that GPR55 activation increases glucose tolerance (P<0.05) and plasma insulin levels (P<0.05), suggesting an in vivo physiological relevance of GPR55 systemic stimulation. Taken together, these results reveal the expression of GPR55 receptors in the endocrine pancreas as well as its function at stimulus-secretion coupling of insulin secretion, suggesting a role in glucose homeostasis. In this context, it may also represent a new target for consideration in the management of type 2 diabetes and related diseases.

Evidence for PPC1, a determinant of the pilei-pellis color of Agaricus bisporus fruitbodies

In the present study, we investigated the genetic basis of mushroom cap color. In first generation hybrids between a brown isolate and the white commercial hybrid U 1, the white trait was recessive. Color was determined using color meter technology in second generation hybrids obtained by crossing the homokaryotic progeny of a first generation hybrid with a homokaryon from U 1. Statistical analysis revealed a bimodal distribution describing two classes of white and not-white hybrids. We postulate that a recessive allele at a single locus (PPC1) encodes the white pilei-pellis color. Joint segregation analyses indicated that PPC1 was linked to the ADH (alcohol dehydrogenase) locus. Through the analysis of the heterokaryotic progeny of the first generation hybrid, a recombination model is proposed in which PPC1 is located between the centromere and the ADH locus.

Conservation of genetic linkage with map expansion in distantly related crosses of Agaricus bisporus

A previous map of the genome of a hybrid strain which had European parents belonging to the secondarily homothallic fungus Agaricus bisporus var. bisporus appeared to be unusually compact, with a particularly recombophobic segment in the central part of chromosome I. A new map of this segment was constructed based on allelic segregations among 103 homokaryotic offspring of an A. bisporus hybrid between a European parent of the var. bisporus and a Californian parent of the heterothallic var. burnettii. Markers completely linked on the previous map were distributed along 28 cM in the new map. These results suggest that the greater recombination rate could be correlated with the outbreeding behaviour of the var. burnettii.