Activin E is a transforming growth factor ß ligand that signals specifically through activin receptor-like kinase 7.

Activins are one of the three distinct subclasses within the greater Transforming growth factor ß (TGFß) superfamily. First discovered for their critical roles in reproductive biology, activins have since been shown to alter cellular differentiation and proliferation. At present, members of the activin subclass include activin A (ActA), ActB, ActC, ActE, and the more distant members myostatin and GDF11. While the biological roles and signaling mechanisms of most activins class members have been well-studied, the signaling potential of ActE has remained largely unknown. Here, we characterized the signaling capacity of homodimeric ActE. Molecular modeling of the ligand:receptor complexes showed that ActC and ActE shared high similarity in both the type I and type II receptor binding epitopes. ActE signaled specifically through ALK7, utilized the canonical activin type II receptors, ActRIIA and ActRIIB, and was resistant to the extracellular antagonists follistatin and WFIKKN. In mature murine adipocytes, ActE invoked a SMAD2/3 response via ALK7, like ActC. Collectively, our results establish ActE as a specific signaling ligand which activates the type I receptor, ALK7.

Elevated circulating BMP9 aggravates pulmonary angiogenesis in hepatopulmonary syndrome rats through ALK1-Endoglin-Smad1/5/9 signalling.

BACKGROUND: Bone morphogenetic protein 9 (BMP9) is a hepatokine that plays a pivotal role in the progression of liver diseases. Moreover, an increasing number of studies have shown that BMP9 is associated with hepatopulmonary syndrome (HPS), but its role in HPS is unclear. Here, we evaluated the influence of CBDL on BMP9 expression and investigated potential mechanisms of BMP9 signalling in HPS. METHODS: We profiled the circulating BMP9 levels in common bile duct ligation-induced HPS rat model, and then investigated the effects and mechanisms of HPS rat serum on pulmonary vascular endothelial dysfunction in rat model, as well as in primarily cultured rat pulmonary microvascular endothelial cells. RESULTS: Our data revealed that circulating BMP9 levels were significantly increased in the HPS rats compared to control group. Besides, the elevated BMP9 in HPS rat serum was not only crucial for promoting endothelial cell proliferation and tube formation through the activin receptor-like kinase1 (ALK1)-Endoglin-Smad1/5/9 pathway, but also important for accumulation of monocytes. Treatments with ALK1-Fc or silencing ALK1 expression to inhibit the BMP9 signalling pathway effectively eliminated these effects. In agreement with these observations, increased circulating BMP9 was associated with an increase in lung vessel density and accumulation of pro-angiogenic monocytes in the microvasculature in HPS rats. CONCLUSIONS: This study provided evidence that elevated circulating BMP9, secreted from the liver, promote pulmonary angiogenesis in HPS rats via ALK1-Endoglin-Smad1/5/9 pathway. In addition, BMP9-regulated pathways are also involved in accumulation of pro-angiogenic monocytes in the pulmonary microvasculature in HPS rats.

Type II BMP and activin receptors BMPR2 and ACVR2A share a conserved mode of growth factor recognition.

BMPR2 is a type II Transforming Growth Factor (TGF)-ß family receptor that is fundamentally associated with pulmonary arterial hypertension (PAH) in humans. BMPR2 shares functional similarities with the type II activin receptors ACVR2A and ACVR2B, as it interacts with an overlapping group of TGF-ß family growth factors (GFs). However, how BMPR2 recognizes GFs remains poorly understood. Here, we solved crystal structures of BMPR2 in complex with the GF activin B and of ACVR2A in complex with the related GF activin A. We show that both BMPR2 and ACVR2A bind GFs with nearly identical geometry using a conserved hydrophobic hot spot, while differences in contacting residues are predominantly found in loop areas. Upon further exploration of the GF-binding spectrum of the two receptors, we found that although many GFs bind both receptors, the high-affinity BMPR2 GFs comprise BMP15, BMP10, and Nodal, whereas those of ACVR2A are activin A, activin B, and GDF11. Lastly, we evaluated GF-binding domain BMPR2 variants found in human PAH patients. We demonstrate that mutations within the GF-binding interface resulted in loss of GF binding, while mutations in loop areas allowed BMPR2 to retain the ability to bind cognate GFs with high affinity. In conclusion, the in vitro activities of BMPR2 variants and the crystal structures reported here indicate biochemically relevant complexes that explain how some GF-binding domain variants can lead to PAH.

Cardiac function modulates endocardial cell dynamics to shape the cardiac outflow tract.

Physical forces are important participants in the cellular dynamics that shape developing organs. During heart formation, for example, contractility and blood flow generate biomechanical cues that influence patterns of cell behavior. Here, we address the interplay between function and form during the assembly of the cardiac outflow tract (OFT), a crucial connection between the heart and vasculature that develops while circulation is under way. In zebrafish, we find that the OFT expands via accrual of both endocardial and myocardial cells. However, when cardiac function is disrupted, OFT endocardial growth ceases, accompanied by reduced proliferation and reduced addition of cells from adjacent vessels. The flow-responsive TGFß receptor Acvrl1 is required for addition of endocardial cells, but not for their proliferation, indicating distinct modes of function-dependent regulation for each of these essential cell behaviors. Together, our results indicate that cardiac function modulates OFT morphogenesis by triggering endocardial cell accumulation that induces OFT lumen expansion and shapes OFT dimensions. Moreover, these morphogenetic mechanisms provide new perspectives regarding the potential causes of cardiac birth defects.

Dorsal-Ventral Gradient of Activin Regulates Strength of GABAergic Inhibition along Longitudinal Axis of Mouse Hippocampus in an Activity-Dependent Fashion.

The functional and neurophysiological distinction between the dorsal and ventral hippocampus affects also GABAergic inhibition. In line with this notion, ventral CA1 pyramidal cells displayed a more dynamic and effective response to inhibitory input compared to their dorsal counterparts. We posit that this difference is effected by the dorsal-ventral gradient of activin A, a member of the transforming growth factor-ß family, which is increasingly recognized for its modulatory role in brain regions involved in cognitive functions and affective behavior. Lending credence to this hypothesis, we found that in slices from transgenic mice expressing a dominant-negative mutant of activin receptor IB (dnActRIB), inhibitory transmission was enhanced only in CA1 neurons of the dorsal hippocampus, where the basal activin A level is much higher than in the ventral hippocampus. We next asked how a rise in endogenous activin A would affect GABAergic inhibition along the longitudinal axis of the hippocampus. We performed ex vivo recordings in wild-type and dnActRIB mice after overnight exposure to an enriched environment (EE), which engenders a robust increase in activin A levels in both dorsal and ventral hippocampi. Compared to control mice from standard cages, the behaviorally induced surge in activin A produced a decline in ventral inhibition, an effect that was absent in slices from dnActRIB mice. Underscoring the essential role of activin in the EE-associated modulation of ventral inhibition, this effect was mimicked by acute application of recombinant activin A in control slices. In summary, both genetic and behavioral manipulations of activin receptor signaling affected the dorsal-ventral difference in synaptic inhibition, suggesting that activin A regulates the strength of GABAergic inhibition in a region-specific fashion.

Efficacy of Immunization against a Novel Synthetic 13-Amino Acid Betaglycan-Binding Peptide Sequence of Inhibin α Subunit on Promoting Fertility in Female Rats.

Inhibins suppress the FSH production in pituitary gonadotrope cells by robustly antagonizing activin signaling by competitively binding to activin type II receptors (ACTR II). The binding of inhibin A to ACTR II requires the presence of its co-receptor, namely, betaglycan. In humans, the critical binding site for betaglycan to inhibin A was identified on the inhibin α subunit. Through conservation analysis, we found that a core 13-amino-acid peptide sequence within the betaglycan-binding epitope on human inhibin α subunit is highly conserved across species. Based on the tandem sequence of such a conserved 13-amino-acid betaglycan-binding epitope (INHα13AA-T), we developed a novel inhibin vaccine and tested its efficacy in promoting female fertility using the female rat as a model. Compared with placebo-immunized controls, INHα13AA-T immunization induced a marked (p < 0.05) antibody generation, enhanced (p < 0.05) ovarian follicle development, and increased ovulation rate and litter sizes. Mechanistically, INHα13AA-T immunization promoted (p < 0.05) pituitary Fshb transcription and increased (p < 0.05) serum FSH and 17ß-estradiol concentrations. In summary, active immunization against INHα13AA-T potently increased FSH levels, ovarian follicle development, ovulation rate and litter sizes, thus causing super-fertility in females. Therefore, immunization against INHα13AA is a promising alternative to the conventional approach of multiple ovulation and super-fertility in mammals.

Regulation of Blood-Brain Barrier Transporters by Transforming Growth Factor-ß/Activin Receptor-Like Kinase 1 Signaling: Relevance to the Brain Disposition of 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Inhibitors (i.e., Statins).

Our laboratory has shown that activation of transforming growth factor- ß (TGF- ß )/activin receptor-like kinase 1 (ALK1) signaling can increase protein expression and transport activity of organic anion transporting polypeptide 1a4 (Oatp1a4) at the blood-brain barrier (BBB). These results are relevant to treatment of ischemic stroke because Oatp transport substrates such as 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (i.e., statins) improve functional neurologic outcomes in patients. Advancement of our work requires determination if TGF- ß /ALK1 signaling alters Oatp1a4 functional expression differently across brain regions and if such disparities affect central nervous system (CNS) statin disposition. Therefore, we studied regulation of Oatp1a4 by the TGF- ß /ALK1 pathway, in vivo, in rat brain microvessels isolated from cerebral cortex, hippocampus, and cerebellum using the ALK1 agonist bone morphogenetic protein-9 (BMP-9) and the ALK1 inhibitor 4-[6-[4-(1-piperazinyl)phenyl]pyrazolo[1,5-a]pyrimidin-3-yl]quinoline dihydrochloride 193189. We showed that Oatp1a4 protein expression and brain distribution of three currently marketed statin drugs (i.e., atorvastatin, pravastatin, and rosuvastatin) were increased in cortex relative to hippocampus and cerebellum. Additionally, BMP-9 treatment enhanced Oatp-mediated statin transport in cortical tissue but not in hippocampus or cerebellum. Although brain drug delivery is also dependent upon efflux transporters, such as P-glycoprotein and/or Breast Cancer Resistance Protein, our data showed that administration of BMP-9 did not alter the relative contribution of these transporters to CNS disposition of statins. Overall, this study provides evidence for differential regulation of Oatp1a4 by TGF- ß /ALK1 signaling across brain regions, knowledge that is critical for development of therapeutic strategies to target Oatps at the BBB for CNS drug delivery. SIGNIFICANCE STATEMENT: Organic anion transporting polypeptides (Oatps) represent transporter targets for brain drug delivery. We have shown that Oatp1a4 statin uptake is higher in cortex versus hippocampus and cerebellum. Additionally, we report that the transforming growth factor- ß /activin receptor-like kinase 1 agonist bone morphogenetic protein-9 increases Oatp1a4 functional expression, but not efflux transporters P-glycoprotein and Breast Cancer Resistance Protein, in cortical brain microvessels. Overall, this study provides critical data that will advance treatment for neurological diseases where drug development has been challenging.

Apolipoprotein A-I Inhibits Transendothelial Transport of Apolipoprotein B-Carrying Lipoproteins and Enhances Its Associated High-Density Lipoprotein Formation.

Caveola-located scavenger receptor type B class I (SR-BI) and activin receptor-like kinase-1 (ALK1) are involved in transendothelial transport of apolipoprotein B-carrying lipoproteins (apoB-LPs). Transport of apoB-LPs though mouse aortic endothelial cells (MAECs) is associated with apoE-carrying high-density lipoprotein (HDL)-like particle formation and apoAI induces raft-located proteins to shift to non-raft membranes by upregulation of ATP-binding cassette transporter A1 (ABCA1). To investigate apoAI's effect on transendothelial transport of apoB-LPs, MAECs and human coronary artery endothelial cells (HCAECs) were treated with apoB-LPs ± apoAI. Our data demonstrated that apoAI neither altered SR-BI and ALK1 expression nor affected apoB-LP binding to MAECs. ApoAI inhibited MAEC uptake, transcellular transport, and intracellular accumulation of apoB-LPs and accelerated their resecretion in MAECs. ApoAI enhanced transendothelial apoB-LP transport-associated HDL-like particle formation, upregulated ABCA1 expression, shifted SR-BI and ALK1 to the non-raft membrane in MAECs, inhibited transcellular transport of apoB-LPs, and enhanced associated HDL-like particle formation in HCAECs. ABCA1 knockdown attenuated apoAI-induced membrane SR-BI and ALK1 relocation and diminished apoAI's effect on transendothelial apoB-LP transport and HDL-like particle formation in MAECs. This suggests that upregulation of ABCA1 expression is a mechanism, whereby apoAI provokes caveola-located receptor relocation, inhibits transendothelial apoB-LP transport, and promotes associated HDL-like particle formation.

Ovarian expression of follicle stimulating hormone and activin receptors genes in a prenatally-androgenized rat model of polycystic ovary syndrome in adulthood.

BACKGROUND: The expression of genes involved in basic pathways, such as folliculogenesis and steroidogenesis may be affected following prenatal androgen exposure. Besides, exposure to androgens during prenatal life plays a central role in developing polycystic ovary syndrome (PCOS) in females in later life. In the present study, we aimed to examine the expression of the follicle stimulating hormone receptor (FSHR) and activin receptor (actR) genes in ovarian granulosa cells (GCs) of a prenatally-androgenized rat model of PCOS in adulthood. METHODS AND RESULTS: In the adult rat model of PCOS and their controls (n = 8 in each group), different phases of the estrous cycle were determined by vaginal smear. Total RNA was extracted from the ovarian GCs using the TRIzol protocol, a reverse transcription kit was used for complementary DNA (cDNA) synthesis, and the expression of FSHR and actR genes was measured by SYBR-Green Real-Time PCR. GraphPad Prism was used for statistical analysis of data, and the t-Student's test was used to compare the results between the two groups. PCOS rats had longer and irregular estrous cycles compared to controls. The expression of FSHR and actR genes were significantly decreased in the rat model of PCOS compared to control rats. In PCOS rats, genes expression ratios for FSHR and actR were 0.91 ± 0.11 times (P = 0.008) and 0.42 ± 0.13 times (P = 0.048) less than controls, respectively. CONCLUSION: Reduced expression of the FSHR and actR genes in ovarian GCs may be one of the mechanisms mediating PCOS-related disorders, especially abnormal ovarian folliculogenesis and ovulation dysfunction, following exposure to androgens during fetal life.

Myostatin regulates the production of fibroblast growth factor 23 (FGF23) in UMR106 osteoblast-like cells.

Myostatin is a signaling molecule produced by skeletal muscle cells (myokine) that inhibits muscle hypertrophy and has further paracrine and endocrine effects in other organs including bone. Myostatin binds to activin receptor type 2B which forms a complex with transforming growth factor-ß type I receptor (TGF-ßRI) and induces intracellular p38MAPK and NFκB signaling. Fibroblast growth factor 23 (FGF23) is a paracrine and endocrine mediator produced by bone cells and regulates phosphate and vitamin D metabolism in the kidney. P38MAPK and NFκB-dependent store-operated Ca2+ entry (SOCE) are positive regulators of FGF23 production. Here, we explored whether myostatin influences the synthesis of FGF23. Fgf23 gene expression was determined by qRT-PCR and FGF23 protein by ELISA in UMR106 osteoblast-like cells. UMR106 cells expressed activin receptor type 2A and B. Myostatin upregulated Fgf23 gene expression and protein production. The myostatin effect on Fgf23 was significantly attenuated by TGF-ßRI inhibitor SB431542, p38MAPK inhibitor SB202190, and NFκB inhibitor withaferin A. Moreover, SOCE inhibitor 2-APB blunted the myostatin effect on Fgf23. Taken together, myostatin is a stimulator of Fgf23 expression in UMR106 cells, an effect at least partially mediated by downstream TGF-ßRI/p38MAPK signaling as well as NFκB-dependent SOCE.

BMP10-mediated ALK1 signaling is continuously required for vascular development and maintenance.

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal-dominant vascular disorder characterized by development of high-flow arteriovenous malformations (AVMs) that can lead to stroke or high-output heart failure. HHT2 is caused by heterozygous mutations in ACVRL1, which encodes an endothelial cell bone morphogenetic protein (BMP) receptor, ALK1. BMP9 and BMP10 are established ALK1 ligands. However, the unique and overlapping roles of these ligands remain poorly understood. To define the physiologically relevant ALK1 ligand(s) required for vascular development and maintenance, we generated zebrafish harboring mutations in bmp9 and duplicate BMP10 paralogs, bmp10 and bmp10-like. bmp9 mutants survive to adulthood with no overt phenotype. In contrast, combined loss of bmp10 and bmp10-like results in embryonic lethal cranial AVMs indistinguishable from acvrl1 mutants. However, despite embryonic functional redundancy of bmp10 and bmp10-like, bmp10 encodes the only required Alk1 ligand in the juvenile-to-adult period. bmp10 mutants exhibit blood vessel abnormalities in anterior skin and liver, heart dysmorphology, and premature death, and vascular defects correlate with increased cardiac output. Together, our findings support a unique role for Bmp10 as a non-redundant Alk1 ligand required to maintain the post-embryonic vasculature and establish zebrafish bmp10 mutants as a model for AVM-associated high-output heart failure, which is an increasingly recognized complication of severe liver involvement in HHT2.

Lipopolysaccharide Detection across the Kingdoms of Life.

Studies in recent years have uncovered a diverse set of eukaryotic receptors that recognize lipopolysaccharide (LPS), the major outer-membrane component of Gram-negative bacteria. Indeed, Toll-like receptors, G-protein-coupled receptors, integrins, receptor-like kinases, and caspases have emerged as important LPS-interacting proteins. In this review, the mammalian receptors that detect LPS are described. I highlight how no host protein is involved in all LPS responses, but a single lipid (phosphatidylinositol-4,5-bisphosphate) regulates many LPS responses, including endocytosis, phagocytosis, inflammation, and pyroptosis. I further describe LPS response systems that operate specifically in plants, and discuss potentially new LPS response systems that await discovery. This diversity of receptors for a single microbial product underscores the importance of host-microbe interactions in multiple kingdoms of life.

Activin Type II Receptor Blockade for Treatment of Muscle Depletion in Chronic Obstructive Pulmonary Disease. A Randomized Trial.

RATIONALE: Bimagrumab is a fully human monoclonal antibody that blocks the activin type II receptors, preventing the activity of myostatin and other negative skeletal muscle regulators. OBJECTIVES: To assess the effects of bimagrumab on skeletal muscle mass and function in patients with chronic obstructive pulmonary disease (COPD) and reduced skeletal muscle mass. METHODS: Sixty-seven patients with COPD (mean FEV1, 1.05 L [41.6% predicted]; aged 40-80 yr; body mass index < 20 kg/m2 or appendicular skeletal muscle mass index ≤ 7.25 [men] and ≤ 5.67 [women] kg/m2), received two doses of either bimagrumab 30 mg/kg intravenously (n = 33) or placebo (n = 34) (Weeks 0 and 8) over 24 weeks. MEASUREMENTS AND MAIN RESULTS: We assessed changes in thigh muscle volume (cubic centimeters) as the primary endpoint along with 6-minute-walk distance (meters), safety, and tolerability. Fifty-five (82.1%) patients completed the study. Thigh muscle volume increased by Week 4 and remained increased at Week 24 in bimagrumab-treated patients, whereas no changes were observed with placebo (Week 4: +5.9% [SD, 3.4%] vs. 0.0% [3.3%], P < 0.001; Week 8: +7.0% [3.7%] vs. -0.7% [2.8%], P < 0.001; Week 16: +7.8% [5.1%] vs. -0.9% [4.5%], P < 0.001; Week 24: +5.0% [4.9%] vs. -1.3% [4.3%], P < 0.001). Over 24 weeks, 6-minute-walk distance did not increase significantly in either group. Adverse events in the bimagrumab group included muscle-related symptoms, diarrhea, and acne, most of which were mild in severity. CONCLUSIONS: Blocking the action of negative muscle regulators through the activin type II receptors with bimagrumab treatment safely increased skeletal muscle mass but did not improve functional capacity in patients with COPD and low muscle mass. Clinical trial registered with www.clinicaltrials.gov (NCT01669174).

Two-factor specification of apoptosis: TGF-ß signaling acts cooperatively with ecdysone signaling to induce cell- and stage-specific apoptosis of larval neurons during metamorphosis in Drosophila melanogaster.

Developmentally regulated programmed cell death (PCD) is one of the key cellular events for precise controlling of neuronal population during postembryonic development of the central nervous system. Previously we have shown that a group of corazonin-producing peptidergic neurons (vCrz) undergo apoptosis in response to ecdysone signaling via ecdysone receptor (EcR)-B isoforms and Ultraspiracle during early phase of metamorphosis. Further utilizing genetic, transgenic, and mosaic analyses, we have found that TGF-ß signaling mediated by a glia-produced ligand, Myoglianin, type-I receptor Baboon (particularly Babo-A isoform) and dSmad2, is also required autonomously for PCD of the vCrz neurons. Our studies show that TGF-ß signaling is not acting epistatically to EcR or vice versa. We also show that ectopic expression of a constitutively active phosphomimetic form of dSmad2 (dSmad2PM) is capable of inducing premature death of vCrz neurons in larva but not other larval neurons. Intriguingly, the dSmad2PM-mediated killing is completely suppressed by coexpression of a dominant-negative form of EcR (EcRDN), suggesting that EcR function is required for the proapoptotic dSmad2PM function. Based on these data, we suggest that TGF-ß and ecdysone signaling pathways act cooperatively to induce vCrz neuronal PCD. We propose that this type of two-factor authentication is a key developmental strategy to ensure the timely PCD of specific larval neurons during metamorphosis.

Alk1 controls arterial endothelial cell migration in lumenized vessels.

Heterozygous loss of the arterial-specific TGFß type I receptor, activin receptor-like kinase 1 (ALK1; ACVRL1), causes hereditary hemorrhagic telangiectasia (HHT). HHT is characterized by development of fragile, direct connections between arteries and veins, or arteriovenous malformations (AVMs). However, how decreased ALK1 signaling leads to AVMs is unknown. To understand the cellular mis-steps that cause AVMs, we assessed endothelial cell behavior in alk1-deficient zebrafish embryos, which develop cranial AVMs. Our data demonstrate that alk1 loss has no effect on arterial endothelial cell proliferation but alters arterial endothelial cell migration within lumenized vessels. In wild-type embryos, alk1-positive cranial arterial endothelial cells generally migrate towards the heart, against the direction of blood flow, with some cells incorporating into endocardium. In alk1-deficient embryos, migration against flow is dampened and migration in the direction of flow is enhanced. Altered migration results in decreased endothelial cell number in arterial segments proximal to the heart and increased endothelial cell number in arterial segments distal to the heart. We speculate that the consequent increase in distal arterial caliber and hemodynamic load precipitates the flow-dependent development of downstream AVMs.

Expression of TGFBR1, TGFBR2, TGFBR3, ACVR1B and ACVR2B is altered in ovaries of cows with cystic ovarian disease.

The objective of this study was to examine the expression of transforming growth factor beta receptor (TGFBR)1, TGFBR2, TGFBR3, activin receptor (ACVR)1B and ACVR2B in ovaries of cows with cystic ovarian disease (COD). The expression of the selected receptors was determined by immunohistochemistry in sections of ovaries from cows with ACTH-induced and spontaneous COD. Expression of TGFBR1 and TGFBR3 was higher in granulosa cells of cysts from cows with spontaneous COD than in tertiary follicles from the control group. Additionally, TGFBR3 expression was higher in granulosa cells of cysts from cows with ACTH-induced COD than in those from the control group and lower in theca cells of spontaneous and ACTH-induced cysts than in tertiary control follicles. There were no changes in the expression of TGFBR2. ACVR1B expression was higher in granulosa cells of tertiary follicles of cows with spontaneous COD than in the control group, whereas ACVR2B expression was higher in cysts of the spontaneous COD group than in tertiary follicles from the control group. The alterations here detected, together with the altered expression of the ligands previously reported, indicate alterations in the response of the ligands in the target cells, modifying their actions at cellular level.

Functional Expression of Organic Anion Transporting Polypeptide 1a4 Is Regulated by Transforming Growth Factor-ß/Activin Receptor-like Kinase 1 Signaling at the Blood-Brain Barrier.

Central nervous system (CNS) drug delivery can be achieved by targeting drug uptake transporters such as Oatp1a4. In fact, many drugs that can improve neurologic outcomes in CNS diseases [3-hydroxy-3-methylglutaryl-CoA reductase inhibitors (i.e., statins)] are organic anion transporting polypeptide (OATP) transport substrates. To date, transport properties and regulatory mechanisms of Oatp1a4 at the blood-brain barrier (BBB) have not been rigorously studied. Such knowledge is critical to develop Oatp1a4 for optimization of CNS drug delivery and for improved treatment of neurological diseases. Our laboratory has demonstrated that the transforming growth factor-ß (TGF-ß)/activin receptor-like kinase 1 (ALK1) signaling agonist bone morphogenetic protein 9 (BMP-9) increases functional expression of Oatp1a4 in rat brain microvessels. Here, we expand on this work and show that BMP-9 treatment increases blood-to-brain transport and brain exposure of established OATP transport substrates (i.e., taurocholate, atorvastatin, and pravastatin). We also demonstrate that BMP-9 activates the TGF-ß/ALK1 pathway in brain microvessels as indicated by increased nuclear translocation of specific Smad proteins associated with signaling mediated by the ALK1 receptor (i.e., pSmad1/5/8). Furthermore, we report that an activated Smad protein complex comprised of phosphorylated Smad1/5/8 and Smad4 is formed following BMP-9 treatment and binds to the promoter of the Slco1a4 gene (i.e., the gene that encodes Oatp1a4). This signaling mechanism causes increased expression of Slco1a4 mRNA. Overall, this study provides evidence that Oatp1a4 transport activity at the BBB is directly regulated by TGF-ß/ALK1 signaling and indicates that this pathway can be targeted for control of CNS delivery of OATP substrate drugs.

Activin signaling balances proliferation and differentiation of ovarian niche precursors and enables adjustment of niche numbers.

How the numbers of niches and resident stem cells within a particular organ are determined during development and how they may be modulated or corrected is a question with significant medical implications. In the larval ovary of Drosophila melanogaster, somatic precursors for niches, and germ cells that will become germline stem cells, co-develop. Somatic precursors proliferate during the first 3 days of larval development. By mid-third instar, adult terminal filament (TF) (part of the germline stem cell niche) cells first appear, and differentiation terminates 24 h later when 16-20 TFs fully form. The developmental sequence responsible for TF cell determination and final TF numbers is only partially understood. We show that TF formation proceeds through several, hitherto uncharacterized stages, which include an early exit from the cell cycle to form TF precursors and two steps of cell shape change to form the mature TF cells. The Activin receptor Baboon (Babo) is required for somatic precursor cell proliferation and therefore determines the pool of TF precursors available for TF differentiation. During the final differentiation stage, Babo facilitates TF and germ cell differentiation, and promotes the accumulation of Broad-Z1, which is also a target of the steroid hormone ecdysone. Epistasis analysis shows that Activin controls cell proliferation in an ecdysone-independent manner and TF differentiation by affecting ecdysone targets. We propose that this mode of function allows Activin to balance proliferation and differentiation, and to equilibrate niche numbers. These results suggest a novel model for how niche numbers are corrected during development.

The overexpression of RXam1, a cassava gene coding for an RLK, confers disease resistance to Xanthomonas axonopodis pv. manihotis.

MAIN CONCLUSION: The overexpression of RXam1 leads to a reduction in bacterial growth of XamCIO136, suggesting that RXam1 might be implicated in strain-specific resistance. Cassava bacterial blight (CBB) caused by Xanthomonas axonopodis pv. manihotis (Xam) is a prevalent disease in all regions, where cassava is cultivated. CBB is a foliar and vascular disease usually controlled through host resistance. Previous studies have found QTLs explaining resistance to several Xam strains. Interestingly, one QTL called XM5 that explained 13% of resistance to XamCIO136 was associated with a similar fragment of the rice Xa21-resistance gene called PCR250. In this study, we aimed to further identify and characterize this fragment and its role in resistance to CBB. Screening and hybridization of a BAC library using the molecular marker PCR250 as a probe led to the identification of a receptor-like kinase similar to Xa21 and were called RXam1 (Resistance to Xam 1). Here, we report the functional characterization of susceptible cassava plants overexpressing RXam1. Our results indicated that the overexpression of RXam1 leads to a reduction in bacterial growth of XamCIO136. This suggests that RXAM1 might be implicated in strain-specific resistance to XamCIO136.

The Increased Transforming Growth Factor-ß Signaling Induced by Diabetes Protects Retinal Vessels.

The roles of transforming growth factor (TGF)-ß in extracellular matrix production and vascular remodeling, coupled with increased TGF-ß expression and signaling in diabetes, suggest TGF-ß as an important contributor to the microangiopathy of diabetic retinopathy and nephropathy. To investigate whether increased TGF-ß signaling could be a therapeutic target for preventing retinopathy, we used a pharmacologic approach (SM16, a selective inhibitor of the type 1 TGF-ß receptor activin receptor-like kinase 5, orally active) to inhibit the increased, but not the basal, Tgf-ß signaling in retinal vessels of diabetic rats. At the level of vascular gene expression, 3.5 months' diabetes induced minimal changes. Diabetes + SM16 for 3 weeks caused widespread changes in gene expression poised to enhance vascular inflammation, thrombosis, leakage, and wall instability; these changes were not observed in control rats given SM16. The synergy of diabetes and SM16 in altering gene expression was not observed in the lung. At the level of vascular network morphology, 7 months' diabetes induced no detectable changes. Diabetes + SM16 for 3 weeks caused instead distorted morphology and decreased density. Thus, in diabetes, retinal vessels become dependent on a small increase in TGF-ß signaling via activin receptor-like kinase 5 to maintain early integrity. The increased TGF-ß signaling may protect against rapid retinopathy progression and should not be a target of inhibitory interventions.