Beta2-adrenergic receptor signaling in CD4+ Foxp3+ regulatory T cells enhances their suppressive function in a PKA-dependent manner.

Beta2-adrenergic receptor (B2AR) signaling is known to impair Th1-cell differentiation and function in a cAMP-dependent way, leading to inhibition of cell proliferation and decreased production of IL-2 and IFN-γ. CD4(+) Foxp3(+) Treg cells play a key role in the regulation of immune responses and are essential for maintenance of self-tolerance. Nevertheless, very little is known about adrenergic receptor expression in Treg cells or the influence of noradrenaline on their function. Here we show that Foxp3(+) Treg cells express functional B2AR. B2AR activation in Treg cells leads to increased intracellular cAMP levels and to protein kinase A (PKA)-dependent CREB phosphorylation. We also found that signaling via B2AR enhances the in vitro suppressive activity of Treg cells. B2AR-mediated increase in Treg-cell suppressive function was associated with decreased IL-2 mRNA levels in responder CD4(+) T cells and improved Treg-cell-induced conversion of CD4(+) Foxp3(-) cells into Foxp3(+) induced Treg cells. Moreover, B2AR signaling increased CTLA-4 expression in Treg cells in a PKA-dependent way. Finally, we found that PKA inhibition totally prevented the B2AR-mediated increase in Treg-cell suppressive function. Our data suggest that sympathetic fibers are able to regulate Treg-cell suppressive activity in a positive manner through B2AR signaling.

Bradykinin receptor 1 activation exacerbates experimental focal and segmental glomerulosclerosis.

Focal and segmental glomerulosclerosis (FSGS) is one of the most important causes of end-stage renal failure. The bradykinin B1 receptor has been associated with tissue inflammation and renal fibrosis. To test for a role of the bradykinin B1 receptor in podocyte injury, we pharmacologically modulated its activity at different time points in an adriamycin-induced mouse model of FSGS. Estimated albuminuria and urinary protein to creatinine ratios correlated with podocytopathy. Adriamycin injection led to loss of body weight, proteinuria, and upregulation of B1 receptor mRNA. Early treatment with a B1 antagonist reduced albuminuria and glomerulosclerosis, and inhibited the adriamycin-induced downregulation of podocin, nephrin, and α-actinin-4 expression. Moreover, delayed treatment with antagonist also induced podocyte protection. Conversely, a B1 agonist aggravated renal dysfunction and even further suppressed the levels of podocyte-related molecules. Thus, we propose that kinin has a crucial role in the pathogenesis of FSGS operating through bradykinin B1 receptor signaling.

Invariant natural killer T cell agonist modulates experimental focal and segmental glomerulosclerosis.

A growing body of evidence demonstrates a correlation between Th2 cytokines and the development of focal and segmental glomerulosclerosis (FSGS). Therefore, we hypothesized that GSL-1, a monoglycosylceramide from Sphingomonas ssp. with pro-Th1 activity on invariant Natural Killer T (iNKT) lymphocytes, could counterbalance the Th2 profile and modulate glomerulosclerosis. Using an adriamycin(ADM)-based model of FSGS, we found that BALB/c mice presented albuminuria and glomerular degeneration in association with a Th2-like pro-fibrogenic profile; these mice also expressed a combination of inflammatory cytokines, such as IL-4, IL-1α, IL-1ß, IL-17, TNF-α, and chemokines, such as RANTES and eotaxin. In addition, we observed a decrease in the mRNA levels of GD3 synthase, the enzyme responsible for GD3 metabolism, a glycolipid associated with podocyte physiology. GSL-1 treatment inhibited ADM-induced renal dysfunction and preserved kidney architecture, a phenomenon associated with the induction of a Th1-like response, increased levels of GD3 synthase transcripts and inhibition of pro-fibrotic transcripts and inflammatory cytokines. TGF-ß analysis revealed increased levels of circulating protein and tissue transcripts in both ADM- and GSL-1-treated mice, suggesting that TGF-ß could be associated with both FSGS pathology and iNKT-mediated immunosuppression; therefore, we analyzed the kidney expression of phosphorylated SMAD2/3 and SMAD7 proteins, molecules associated with the deleterious and protective effects of TGF-ß, respectively. We found high levels of phosphoSMAD2/3 in ADM mice in contrast to the GSL-1 treated group in which SMAD7 expression increased. These data suggest that GSL-1 treatment modulates the downstream signaling of TGF-ß through a renoprotective pathway. Finally, GSL-1 treatment at day 4, a period when proteinuria was already established, was still able to improve renal function, preserve renal structure and inhibit fibrogenic transcripts. In conclusion, our work demonstrates that the iNKT agonist GSL-1 modulates the pathogenesis of ADM-induced glomerulosclerosis and may provide an alternative approach to disease management.