Exogenous mesenchymal stem cells localize to the kidney by means of CD44 following acute tubular injury

Mesenchymal stem cells (MSC) were recently shown to migrate to injured tissues when transplanted systemically. The mechanisms underlying the migration and homing of these cells is, however, unclear. In this study, we examine the role of CD44 and its major ligand, hyaluronic acid, in the trafficking of intravenously injected MSC in the glycerol-induced mouse model of acute renal failure (ARF). In vitro, hyaluronic acid promoted a dose-dependent migration of the stem cells that was inhibited by an anti-CD44 blocking monoclonal antibody. In vivo, stem cells injected into mice with ARF migrated to the injured kidney where hyaluronic acid expression was increased. Their presence correlated with morphological and functional recovery. Renal localization of the MSC was blocked by pre-incubation with the CD44 blocking antibody or by soluble hyaluronic acid. Stem cells derived from CD44 knockout mice did not localize to the injured kidney and did not accelerate morphological or functional recovery. Reconstitution by transfection of CD44 knockout stem cells with cDNA encoding wild-type CD44, but not a loss of function CD44 unable to bind hyaluronic acid, restored in vitro migration and in vivo localization of the cells to injured kidneys. We suggest that CD44 and hyaluronic acid interactions recruit exogenous MSC to injured renal tissue and enhance renal regeneration.

Decreased cannabinoid CB1 receptor mRNA levels and immunoreactivity in pituitary hyperplasia induced by prolonged exposure to estrogens

Recent studies have demonstrated that cannabinoid CB1 receptor gene expression in the anterior pituitary gland is under the influence of estrogens. Because these receptors have been recently involved in the development of several types of cancer, it would be interesting to examine the changes produced in these receptors by the development of pituitary hyperplasia after a chronic exposure to estrogens. To this end, we measured mRNA levels and immunoreactivity for the CB1 receptor in the anterior pituitary gland of rats implanted with silastic capsules containing diethylstilbestrod (DES), a synthetic estrogen, or empty capsules. Results were as follows. Induction of pituitary hyperplasia with DES produced the expected body weight loss (-38.4%) and increase in pituitary weight (5-fold) and plasma prolactin (PRL) levels (90-fold). In hyperplastic pituitaries, both CB1 receptor mRNA levels and immunoreactivity decreased significantly (-79.4% and -63.2% respectively). Double immuno-labelling studies demonstrated that CB1 receptors colocalized, in hyperplastic pituitaries, with PRL- or luteinizing hormone-containing cells, as they did in normal pituitaries. In summary, estrogen-induced pituitary hyperplastia was associated with a marked reduction in CB1 receptors, despite the fact that these receptors were located, among others, on lactotroph cells which develop hyperplasia during DES exposure. Whether this decrease is involved in the ethiology of pituitary hyperplasia and whether the pharmacological activation of these receptors might affect this process are presently unknown, but this will be subjected of further research.