Repeated platelet activation and the potential of previously activated platelets to contribute to thrombus formation

BACKGROUND

Especially in disease conditions, platelets can encounter activating agents in circulation.

OBJECTIVES

To investigate the extent to which previously activated platelets can be reactivated and whether in-and reactivation applies to different aspects of platelet activation and thrombus formation.

METHODS

Short-and long-term effects of glycoprotein VI (GPVI) and G protein-coupled receptor (GPCR) stimulation on platelet activation and aggregation potential were compared via flow cytometry and plate-based aggregation. Using fluorescence and electron microscopy, we assessed platelet morphology and content, as well as thrombus formation.

RESULTS

After 30 minutes of stimulation with thrombin receptor activator peptide 6 (TRAP6) or adenosine diphosphate (ADP), platelets secondarily decreased in PAC-1 binding and were less able to aggregate. The reversibility of platelets after thrombin stimulation was concentration dependent. Reactivation was possible via another receptor. In contrast, cross-linked collagen-related peptide (CRP-XL) or high thrombin stimulation evoked persistent effects in α_IIbβ₃ activation and platelet aggregation. However, after 60 minutes of CRP-XL or high thrombin stimulation, when α_IIbβ₃ activation slightly decreased, restimulation with ADP or CRP-XL, respectively, increased integrin activation again. Compatible with decreased integrin activation, platelet morphology was reversed. Interestingly, reactivation of reversed platelets again resulted in shape change and if not fully degranulated, additional secretion. Moreover, platelets that were previously activated with TRAP6 or ADP regained their potential to contribute to thrombus formation under flow. On the contrary, prior platelet triggering with CRP-XL was accompanied by prolonged platelet activity, leading to a decreased secondary platelet adhesion under flow.

CONCLUSION

This work emphasizes that prior platelet activation can be reversed, whereafter platelets can be reactivated through a different receptor. Reversed, previously activated platelets can contribute to thrombus formation.

Taste receptors in CRS, what is the evidence?: a systematic review

BACKGROUND

Bitter (T2Rs) and sweet (T1Rs) taste receptors are involved in the innate immune response of the sinonasal cavity and associated with chronic rhinosinusitis (CRS). Growing evidence suggests extraoral taste receptors as relevant biomarkers, but current understanding is incomplete. This systematic review synthesizes current evidence of extraoral taste receptors in CRS.

METHODS

PubMed, Embase, Cochrane, Web of Science, and Scopus were reviewed in accordance with Preferred Reporting Items for Systemic Reviews and Meta-Analyses (PRISMA) guidelines and included studies of genotypic and phenotypic T2R/T1R receptor status in CRS patients.

RESULTS

Twenty-two studies with 3,845 patients were included. Seventeen studies evaluated genotype and 10 evaluated taste phenotypes. Four of six studies examining the haplotype distribution of the T2R, TAS2R38, demonstrated increased AVI/AVI haplotype ("non-taster") frequency in CRS. Meanwhile, two studies demonstrated decreased bitter sensitivity in CRS with nasal polyposis (CRSwNP) while three other studies reported decreased bitter sensitivity only in CRS without nasal polyposis (CRSsNP). Findings regarding sweet sensitivity were mixed. Three studies with cystic fibrosis patients (n=1,393) were included. Studies investigating the association between clinical outcomes and TAS2R38 alleles were limited, but the nonfunctional combination of AVI/AVI was associated with increased utilization of sinus surgery and, in CRSsNP patients, with poorer improvement of symptoms postoperatively.

CONCLUSIONS

Both genotypic and phenotypic assessments of T2Rs suggest a potential association with CRS, particularly CRSsNP. However, limited evidence and mixed conclusions cloud the role of T2Rs in CRS. Future investigations should aim to increase diverse populations, broaden institutional diversity, examine T1Rs, and utilize uniform assessments. This article is protected by copyright. All rights reserved.

Deletion of GPR21 improves glucose homeostasis and inhibits the CCL2-CCR2 axis by divergent mechanisms

INTRODUCTION

A potential role for the orphan G protein-coupled receptor, GPR21, in linking immune cell infiltration into tissues and obesity-induced insulin resistance has been proposed, although limited studies in mice are complicated by non-selective deletion of Gpr21.

RESEARCH DESIGN AND METHODS

We hypothesized that a Gpr21-selective knockout mouse model, coupled with type 2 diabetes patient samples, would clarify these issues and enable clear assessment of GPR21 as a potential therapeutic target.

RESULTS

High-fat feeding studies in Gpr21^-/- mice revealed improved glucose tolerance and modest changes in inflammatory gene expression. Gpr21^-/- monocytes and intraperitoneal macrophages had selectively impaired chemotactic responses to monocyte chemoattractant protein (MCP)-1, despite unaltered expression of Ccr2. Further genotypic analysis revealed that chemotactic impairment was due to dysregulated monocyte polarization. Patient samples revealed elevated GPR21 expression in peripheral blood mononuclear cells in type 2 diabetes, which was correlated with both %HbA1c and fasting plasma glucose levels.

CONCLUSIONS

Collectively, human and mouse data suggest that GPR21 influences both glucose homeostasis and MCP-1/CCL2-CCR2-driven monocyte migration. However, a Gpr21^-/- bone marrow transplantation and high-fat feeding study in mice revealed no effect on glucose homeostasis, suggesting that there is no (or limited) overlap in the mechanism involved for monocyte-driven inflammation and glucose homeostasis.

Lgr4 Governs a Pro-Inflammatory Program in Macrophages to Antagonize Post-Infarction Cardiac Repair

RATIONALE

Macrophages are critically involved in wound healing following myocardial infarction (MI). Lgr4, a member of LGR (leucine-rich repeat-containing G protein-coupled receptor) family, is emerging as a regulator of macrophage-associated immune responses. However, the contribution of Lgr4 to macrophage phenotype and function in the context of MI remains unclear.

OBJECTIVE

To determine the role of macrophage Lgr4 in MI and to dissect the underlying mechanisms.

METHODS AND RESULTS

During early inflammatory phase of MI, infarct macrophages rather than neutrophils expressed high level of Lgr4. Macrophage-specific Lgr4 knockout mice had no baseline cardiovascular defects but manifested improved heart function, modestly reduced infarct size, decreased early mortality due to cardiac rupture, and ameliorated adverse remodeling after MI. Improved outcomes in macrophage-specific Lgr4 knockout mice subjected to MI were associated with mitigated ischemic injury and optimal infarct healing, as determined by reduction of cardiac apoptosis in the peri-infarct zone, attenuation of local myocardial inflammatory response, decrease of matrix metalloproteinase expression in the infarct, enhancement of angiogenesis, myofibroblast proliferation, and collagen I deposition in reparative granulation tissue as well as formation of collagen-rich scar. More importantly, macrophage-specific Lgr4 knockout infarcts had reduced numbers of infiltrating leukocytes and inflammatory macrophages but harbored abundant reparative macrophage subsets. Lgr4-null infarct macrophages exhibited a less inflammatory transcriptional signature. These findings were further supported by transcriptomic profiling data showing repression of multiple pathways and broad-spectrum genes associated with proinflammatory responses in macrophage-specific Lgr4 knockout infarcts. Notably, we discovered that Lgr4-mediated functional phenotype programing in infarct macrophages was at least partly attributed to regulation of AP (activator protein)-1 activity. We further demonstrated that the synergistic effects of Lgr4 on AP-1 activation in inflammatory macrophages occurred via enhancing CREB (cAMP response element-binding protein)-mediated c-Fos, Fosl1, and Fosb transactivation.

CONCLUSIONS

Together, our data highlight the significance of Lgr4 in governing proinflammatory phenotype of infarct macrophages and postinfarction repair.

TBX20 Regulates Angiogenesis Through the Prokineticin 2-Prokineticin Receptor 1 Pathway

BACKGROUND

Angiogenesis is integral for embryogenesis, and targeting angiogenesis improves the outcome of many pathological conditions in patients. TBX20 is a crucial transcription factor for embryonic development, and its deficiency is associated with congenital heart disease. However, the role of TBX20 in angiogenesis has not been described.

METHODS

Loss- and gain-of-function approaches were used to explore the role of TBX20 in angiogenesis both in vitro and in vivo. Angiogenesis gene array was used to identify key downstream targets of TBX20.

RESULTS

Unbiased gene array survey showed that TBX20 knockdown profoundly reduced angiogenesis-associated PROK2 (prokineticin 2) gene expression. Indeed, loss of TBX20 hindered endothelial cell migration and in vitro angiogenesis. In a murine angiogenesis model using subcutaneously implanted Matrigel plugs, we observed that TBX20 deficiency markedly reduced PROK2 expression and restricted intraplug angiogenesis. Furthermore, recombinant PROK2 administration enhanced angiogenesis and blood flow recovery in murine hind-limb ischemia. In zebrafish, transient knockdown of tbx20 by morpholino antisense oligos or genetic disruption of tbx20 by CRISPR/Cas9 impaired angiogenesis. Furthermore, loss of prok2 or its cognate receptor prokr1a also limited angiogenesis. In contrast, overexpression of prok2 or prokr1a rescued the impaired angiogenesis in tbx20-deficient animals.

CONCLUSIONS

Our study identifies TBX20 as a novel transcription factor regulating angiogenesis through the PROK2-PROKR1 (prokineticin receptor 1) pathway in both development and disease and reveals a novel mode of angiogenic regulation whereby the TBX20-PROK2-PROKR1 signaling cascade may act as a "biological capacitor" to relay and sustain the proangiogenic effect of vascular endothelial growth factor. This pathway may be a therapeutic target in the treatment of diseases with dysregulated angiogenesis.

Retention of aberrant cortisol secretion in a patient with bilateral macronodular adrenal hyperplasia after unilateral adrenalectomy

Aberrant cortisol secretion responses after exogenous stimuli such as upright posture, eating a mixed meal or receiving agents influencing aberrant G-protein-coupled receptors in adrenal glands, are often observed in patients with bilateral macronodular adrenal hyperplasia (BMAH). However, little is known about whether this aberrant response is retained after unilateral adrenalectomy. Here, we describe a 61-year-old postmenopausal Japanese woman with unsatisfactorily controlled hypertension who was referred to us for further investigation due to her pre-obesity characteristics (body mass index 28.4 kg/m²). Cushing’s signs and serum cortisol at 16.2 µg/dL with undetectable adrenocorticotropic hormone indicated adrenal Cushing’s syndrome. Adrenal imaging revealed bilaterally enlarged adrenal glands with 131-I adosterol uptake; hence, BMAH was diagnosed. Preoperatively, in vivo screening for aberrant adrenal receptors revealed an aberrant response of cortisol secretion on metoclopramide challenge. The patient underwent unilateral adrenalectomy; thereafter, glucocorticoid replacement therapy was reduced to hydrocortisone 15 mg/day at postoperative day 6. Fasting morning serum cortisol level measured at postoperative day 8 was 2.96 µg/dL, suggesting adrenal insufficiency. However, following metoclopramide administration serum cortisol level rose to 19.7 µg/dL, indicating potential efficient adrenal function. Aberrant cortisol secretory capacity was thus preserved in BMAH, even in a state of adrenal insufficiency after unilateral adrenalectomy. Caution should be exercised when assessing the hypothalamus-pituitary-adrenal axis, because in this patient, a high cortisol level did not guarantee appropriate adrenal function when the patient was challenged by exogenous stimuli.

Melatonin signalling and type 2 diabetes risk: too little, too much or just right?

Of the associations of genetic variants with type 2 diabetes, the one of an SNP in an intron of the gene encoding the melatonin receptor 1B (MTNR1B) has been remarkably robust. Work from our group and others has provided support for a model where carriers of this risk G allele exhibit increased MTNR1B expression in islets of Langerhans. Most published studies to date favour that melatonin's action on the beta cell is inhibition of insulin secretion. Hence, our model proposes that this inhibitory effect of melatonin is exaggerated in carriers of the MTNR1B risk G allele. This would explain why this genetic association causes reduced insulin secretion and greater risk of future type 2 diabetes, as has been observed in numerous studies. Concurrently, another body of work has shown that rare MTNR1B alleles, which could perturb receptor function, also associate with type 2 diabetes. In this commentary, it is suggested that such apparently conflicting observations can be reconciled by the fact that non-coding (intronic; frequent) and coding (exonic; rare) alleles of MTNR1B give rise to different phenotypes. Thus, altered gene transcription may explain why SNPs, which do not alter coding sequences, exhibit cell-specific effects. In contrast, SNPs that change protein sequences are more likely to exert generalised effects since an altered protein will appear in all cells expressing the gene.

Diversity and impact of rare variants in genes encoding the platelet G protein-coupled receptors

Platelet responses to activating agonists are influenced by common population variants within or near G protein-coupled receptor (GPCR) genes that affect receptor activity. However, the impact of rare GPCR gene variants is unknown. We describe the rare single nucleotide variants (SNVs) in the coding and splice regions of 18 GPCR genes in 7,595 exomes from the 1,000-genomes and Exome Sequencing Project databases and in 31 cases with inherited platelet function disorders (IPFDs). In the population databases, the GPCR gene target regions contained 740 SNVs (318 synonymous, 410 missense, 7 stop gain and 6 splice region) of which 70 % had global minor allele frequency (MAF) < 0.05 %. Functional annotation using six computational algorithms, experimental evidence and structural data identified 156/740 (21 %) SNVs as potentially damaging to GPCR function, most commonly in regions encoding the transmembrane and C-terminal intracellular receptor domains. In 31 index cases with IPFDs (Gi-pathway defect n=15; secretion defect n=11; thromboxane pathway defect n=3 and complex defect n=2) there were 256 SNVs in the target regions of 15 stimulatory platelet GPCRs (34 unique; 12 with MAF< 1 % and 22 with MAF≥ 1 %). These included rare variants predicting R122H, P258T and V207A substitutions in the P2Y12 receptor that were annotated as potentially damaging, but only partially explained the platelet function defects in each case. Our data highlight that potentially damaging variants in platelet GPCR genes have low individual frequencies, but are collectively abundant in the population. Potentially damaging variants are also present in pedigrees with IPFDs and may contribute to complex laboratory phenotypes.

Expression and Function of LPA1 in Bladder Cancer

PURPOSE

LPA is one of several physiologically active lipid mediators that promote cell proliferation and invasion, and are present in serum, ascites and urine. LPA receptor is a G-protein coupled receptor that is considered a potential therapeutic target for some malignant cancers. We evaluated the expression of LPA receptors in bladder cancer and the effect of LPA in bladder cancer invasion.

MATERIALS AND METHODS

Using real-time polymerase chain reaction and immunohistochemical staining we determined LPA receptor expression in bladder cancer specimens from patients with bladder cancer, including 12 with Ta or T1 and 15 with T2-T4 disease. ROCK expression, myosin light chain phosphorylation and Matrigel™ invasion assays were done and morphological observations were made to assess LPA effects in T24 cells, which were derived from bladder cancer.

RESULTS

Notably LPA1 mRNA expression was significantly higher in muscle invasive bladder cancer specimens than in nonmuscle invasive specimens. Strong LPA1 expression was evident on cell membranes in muscle invasive specimens. T24 cell invasion was increased by LPA treatment and invasiveness was decreased by LPA1 siRNA or LPA1 inhibitor. LPA treatment increased ROCK1 expression and myosin light chain phosphorylation, and induced morphological changes, including lamellipodia formation and cell rounding.

CONCLUSIONS

Results indicate that LPA signaling via LPA1 activation promoted bladder cancer invasion. LPA1 might be useful to detect bladder cancer with highly invasive potential and become a new therapeutic target for invasive bladder cancer treatment.