ATP11C is critical for the internalization of phosphatidylserine and differentiation of B lymphocytes.

Subcompartments of the plasma membrane are believed to be critical for lymphocyte responses, but few genetic tools are available to test their function. Here we describe a previously unknown X-linked B cell-deficiency syndrome in mice caused by mutations in Atp11c, which encodes a member of the P4 ATPase family thought to serve as 'flippases' that concentrate aminophospholipids in the cytoplasmic leaflet of cell membranes. Defective ATP11C resulted in a lower rate of phosphatidylserine translocation in pro-B cells and much lower pre-B cell and B cell numbers despite expression of pre-rearranged immunoglobulin transgenes or enforced expression of the prosurvival protein Bcl-2 to prevent apoptosis and abolished pre-B cell population expansion in response to a transgene encoding interleukin 7. The only other abnormalities we noted were anemia, hyperbilirubinemia and hepatocellular carcinoma. Our results identify an intimate connection between phospholipid transport and B lymphocyte function.

cGMP-Elevating Compounds and Ischemic Conditioning Provide Cardioprotection Against Ischemia and Reperfusion Injury via Cardiomyocyte-Specific BK Channels.

BACKGROUND: The nitric oxide-sensitive guanylyl cyclase/cGMP-dependent protein kinase type I signaling pathway can afford protection against the ischemia/reperfusion injury that occurs during myocardial infarction. Reportedly, voltage and Ca2+-activated K+ channels of the BK type are stimulated by cGMP/cGMP-dependent protein kinase type I, and recent ex vivo studies implicated that increased BK activity favors the survival of the myocardium at ischemia/reperfusion. It remains unclear, however, whether the molecular events downstream of cGMP involve BK channels present in cardiomyocytes or in other cardiac cell types. METHODS: Gene-targeted mice with a cardiomyocyte- or smooth muscle cell-specific deletion of the BK (CMBK or SMBK knockouts) were subjected to the open-chest model of myocardial infarction. Infarct sizes of the conditional mutants were compared with litter-matched controls, global BK knockout, and wild-type mice. Cardiac damage was assessed after mechanical conditioning or pharmacological stimulation of the cGMP pathway and by using direct modulators of BK. Long-term outcome was studied with respect to heart functions and cardiac fibrosis in a chronic myocardial infarction model. RESULTS: Global BK knockouts and CMBK knockouts, in contrast with SMBK knockouts, exhibited significantly larger infarct sizes compared with their respective controls. Ablation of CMBK resulted in higher serum levels of cardiac troponin I and elevated amounts of reactive oxygen species, lower phosphorylated extracellular receptor kinase and phosphorylated AKT levels and an increase in myocardial apoptosis. Moreover, CMBK was required to allow beneficial effects of both nitric oxide-sensitive guanylyl cyclase activation and inhibition of the cGMP-degrading phosphodiesterase-5, ischemic preconditioning, and postconditioning regimens. To this end, after 4 weeks of reperfusion, fibrotic tissue increased and myocardial strain echocardiography was significantly compromised in CMBK-deficient mice. CONCLUSIONS: Lack of CMBK channels renders the heart more susceptible to ischemia/reperfusion injury, whereas the pathological events elicited by ischemia/reperfusion do not involve BK in vascular smooth muscle cells. BK seems to permit the protective effects triggered by cinaciguat, riociguat, and different phosphodiesterase-5 inhibitors and beneficial actions of ischemic preconditioning and ischemic postconditioning by a mechanism stemming primarily from cardiomyocytes. This study establishes mitochondrial CMBK channels as a promising target for limiting acute cardiac damage and adverse long-term events that occur after myocardial infarction.

ZBTB7B (Th-POK) regulates the development of IL-17-producing CD1d-restricted mouse NKT cells.

CD1d-dependent NKT cells represent a heterogeneous family of effector T cells including CD4(+)CD8(-) and CD4(-)CD8(-) subsets that respond to glycolipid Ags with rapid and potent cytokine production. NKT cell development is regulated by a unique combination of factors, however very little is known about factors that control the development of NKT subsets. In this study, we analyze a novel mouse strain (helpless) with a mis-sense mutation in the BTB-POZ domain of ZBTB7B and demonstrate that this mutation has dramatic, intrinsic effects on development of NKT cell subsets. Although NKT cell numbers are similar in Zbtb7b mutant mice, these cells are hyperproliferative and most lack CD4 and instead express CD8. Moreover, the majority of ZBTB7B mutant NKT cells in the thymus are retinoic acid-related orphan receptor γt positive, and a high frequency produce IL-17 while very few produce IFN-γ or other cytokines, sharply contrasting the profile of normal NKT cells. Mice heterozygous for the helpless mutation also have reduced numbers of CD4(+) NKT cells and increased production of IL-17 without an increase in CD8(+) cells, suggesting that ZBTB7B acts at multiple stages of NKT cell development. These results reveal ZBTB7B as a critical factor genetically predetermining the balance of effector subsets within the NKT cell population.

Linagliptin treatment is associated with altered cobalamin (VitB12) homeostasis in mice and humans.

Linagliptin is a dipeptidyl peptidase-4 (DPP-4) inhibitor used for the treatment of type 2 diabetes, with additional beneficial effects for the kidney. Treatment of mice with linagliptin revealed increased storage of cobalamin (Cbl, Vitamin B12) in organs if a standard Cbl diet (30 µg Cbl/kg chow) is given. In order to translate these findings to humans, we determined methylmalonic acid (MMA), a surrogate marker of functional Cbl homeostasis, in human plasma and urine samples (n = 1092) from baseline and end of trial (6 months after baseline) of the previously completed MARLINA-T2D clinical trial. We found that individuals with medium Cbl levels (MMA between 50 and 270 nmol/L for plasma, 0.4 and 3.5 µmol/mmol creatinine for urine, at baseline and end of trial) exhibited higher MMA values at the end of study in placebo compared with linagliptin. Linagliptin might inhibit the N-terminal degradation of the transcobalamin receptor CD320, which is necessary for uptake of Cbl into endothelial cells. Because we demonstrate that linagliptin led to increased organ levels of Cbl in mice, sustained constant medium MMA levels in humans, and inhibited CD320 processing by DPP-4 in-vitro, we speculate that linagliptin promotes intra-cellular uptake of Cbl by prolonging half-life of CD320.

Antifibrotic effects of low dose SGLT2 Inhibition with empagliflozin in comparison to Ang II receptor blockade with telmisartan in 5/6 nephrectomised rats on high salt diet.

To date, the lowest protective SGLT2 inhibitor dose is unknown. We initially performed a dose-response pilot study in normal rats. Based on the results of this pilot study we compared the cardio-renal effects of the SGLT-2 inhibitor empagliflozin, with placebo or telmisartan in rats with 5/6 nephrectomy (5/6 Nx) on a high salt diet (HSD). The experimental set up was as follows: Sham operation (Sham) with normal diet and placebo; 5/6 Nx with 2% HSD and placebo; 5/6 Nx with HSD and empagliflozin (0.6 mg/kg/day, bid); 5/6 Nx with HSD and telmisartan (5 mg/kg/day, qd). Empagliflozin treatment increased urinary glucose excretion, in parallel to empagliflozin plasma levels, in a dose-dependent manner starting at doses of 1 mg/kg in the pilot study. 5/6Nx rats on HSD treated with this low empagliflozin dose showed significantly reduced cardiac (-34.85%; P < 0.05) and renal (-33.68%; P < 0.05) fibrosis in comparison to 5/6Nx rats on HSD treated with placebo. These effects were comparable to the effects observed when implementing the standard dose (5 mg/kg/day) of telmisartan (cardiac fibrosis: -36.37%; P < 0.01; renal fibrosis; -43.96%; P < 0.01). RNA-sequencing followed by confirmatory qRT-PCR revealed that both telmisartan and empagliflozin exert their cardiac effects on genes involved in vascular cell stability and cardiac iron homeostasis, whereas in the kidneys expression of genes involved in endothelial function and oxidative stress were differentially expressed. Urinary adenosine excretion, a surrogate marker of the tubuloglomerular feedback (TGF) mechanism, was not affected. In conclusion, the antifibrotic properties of low dose empagliflozin were comparable to a standard dose of telmisartan. The underlying pathways appear to be TGF independent.

Cardioprotection by ischemic postconditioning and cyclic guanosine monophosphate-elevating agents involves cardiomyocyte nitric oxide-sensitive guanylyl cyclase.

Aims: It has been suggested that the nitric oxide-sensitive guanylyl cyclase (NO-GC)/cyclic guanosine monophosphate (cGMP)-dependent signalling pathway affords protection against cardiac damage during acute myocardial infarction (AMI). It is, however, not clear whether the NO-GC/cGMP system confers its favourable effects through a mechanism located in cardiomyocytes (CMs). The aim of this study was to evaluate the infarct-limiting effects of the endogenous NO-GC in CMs in vivo. Methods and results: Ischemia/reperfusion (I/R) injury was evaluated in mice with a CM-specific deletion of NO-GC (CM NO-GC KO) and in control siblings (CM NO-GC CTR) subjected to an in vivo model of AMI. Lack of CM NO-GC resulted in a mild increase in blood pressure but did not affect basal infarct sizes after I/R. Ischemic postconditioning (iPost), administration of the phosphodiesterase-5 inhibitors sildenafil and tadalafil as well as the NO-GC activator cinaciguat significantly reduced the amount of infarction in control mice but not in CM NO-GC KO littermates. Interestingly, NS11021, an opener of the large-conductance and Ca2+-activated potassium channel (BK), an important downstream effector of cGMP/cGKI in the cardiovascular system, protects I/R-exposed hearts of CM NO-GC proficient and deficient mice. Conclusions: These findings demonstrate an important role of CM NO-GC for the cardioprotective signalling following AMI in vivo. CM NO-GC function is essential for the beneficial effects on infarct size elicited by iPost and pharmacological elevation of cGMP; however, lack of CM NO-GC does not seem to disrupt the cardioprotection mediated by the BK opener NS11021.