Specific oxylipins enhance vertebrate hematopoiesis via the receptor GPR132.

Epoxyeicosatrienoic acids (EETs) are lipid-derived signaling molecules with cardioprotective and vasodilatory actions. We recently showed that 11,12-EET enhances hematopoietic induction and engraftment in mice and zebrafish. EETs are known to signal via G protein-coupled receptors, with evidence supporting the existence of a specific high-affinity receptor. Identification of a hematopoietic-specific EET receptor would enable genetic interrogation of EET signaling pathways, and perhaps clinical use of this molecule. We developed a bioinformatic approach to identify an EET receptor based on the expression of G protein-coupled receptors in cell lines with differential responses to EETs. We found 10 candidate EET receptors that are expressed in three EET-responsive cell lines, but not expressed in an EET-unresponsive line. Of these, only recombinant GPR132 showed EET-responsiveness in vitro, using a luminescence-based ß-arrestin recruitment assay. Knockdown of zebrafish gpr132b prevented EET-induced hematopoiesis, and marrow from GPR132 knockout mice showed decreased long-term engraftment capability. In contrast to high-affinity EET receptors, GPR132 is reported to respond to additional hydroxy-fatty acids in vitro, and we found that these same hydroxy-fatty acids enhance hematopoiesis in the zebrafish. We conducted structure-activity relationship analyses using both cell culture and zebrafish assays on diverse medium-chain fatty acids. Certain oxygenated, unsaturated free fatty acids showed high activation of GPR132, whereas unoxygenated or saturated fatty acids had lower activity. Absence of the carbon-1 position carboxylic acid prevented activity, suggesting that this moiety is required for receptor activation. GPR132 responds to a select panel of oxygenated polyunsaturated fatty acids to enhance both embryonic and adult hematopoiesis.

A Case of a Negative Urine Pregnancy Test in a Multiple Gestation Pregnancy.

Urine pregnancy tests (UPTs) are a highly reliable method of detecting pregnancy, with reported 100% sensitivity and 99.2% specificity. This test relies on the detection of ß-human chorionic gonadotropin (ß-hCG) molecules in the urine through a two-site sandwich immunoassay. Although a nearly perfect test, it is common knowledge that this test can be falsely negative if performed too early in the pregnancy when urinary ß-hCG concentrations fall below detectable levels. Less commonly known is that the test may provide a false-negative result when urinary ß-hCG concentrations are extremely elevated, such as gestational trophoblastic disease or multiple gestations. Here, we present a case of a patient with a prior positive urine pregnancy test who presents with symptoms consistent with early pregnancy. Repeat testing resulted in a negative urine pregnancy test. Additional workup revealed significantly elevated serum quantitative ß-hCG and bedside ultrasound revealed multiple gestation intrauterine pregnancy. The patient ultimately delivered triplets by repeated caesarean section. It is important for physicians to understand and recognize the limitations of the urine pregnancy test in order to best facilitate care for patients who may have a false-negative pregnancy test result, as there are significant risks of improper patient management with a multiple gestation pregnancy or gestational trophoblastic disease.