Perspectives on polarity - exploring biological asymmetry across scales

In this Perspective, Journal of Cell Science invited researchers working on cell and tissue polarity to share their thoughts on unique, emerging or open questions relating to their field. The goal of this article is to feature 'voices' from scientists around the world and at various career stages, to bring attention to innovative and thought-provoking topics of interest to the cell biology community. These voices discuss intriguing questions that consider polarity across scales, evolution, development and disease. What can yeast and protists tell us about the evolution of cell and tissue polarity in animals? How are cell fate and development influenced by emerging dynamics in cell polarity? What can we learn from atypical and extreme polarity systems? How can we arrive at a more unified biophysical understanding of polarity? Taken together, these pieces demonstrate the broad relevance of the fascinating phenomenon of cell polarization to diverse fundamental biological questions.

Loss of polarity regulators initiates gasdermin-E-mediated pyroptosis in syncytiotrophoblasts

The syncytiotrophoblast is a human epithelial cell that is bathed in maternal blood on the maternal-facing surface of the human placenta. It therefore acts as a barrier and exchange interface between the mother and fetus. Syncytiotrophoblast dysfunction is a feature of pregnancy pathologies, like preeclampsia. Dysfunctional syncytiotrophoblasts display a loss of microvilli, which is a marker of aberrant apical-basal polarization, but little data exist about the regulation of syncytiotrophoblast polarity. Atypical PKC isoforms are conserved polarity regulators. Thus, we hypothesized that aPKC isoforms regulate syncytiotrophoblast polarity. Using human placental explant culture and primary trophoblasts, we found that loss of aPKC activity or expression induces syncytiotrophoblast gasdermin-E-dependent pyroptosis, a form of programmed necrosis. We also establish that TNF-α induces an isoform-specific decrease in aPKC expression and gasdermin-E-dependent pyroptosis. Therefore, aPKCs are homeostatic regulators of the syncytiotrophoblast function and a pathogenically relevant pro-inflammatory cytokine leads to the induction of programmed necrosis at the maternal-fetal interface. Hence, our results have important implications for the pathobiology of placental disorders like preeclampsia.

Cell polarity signaling in the regulation of syncytiotrophoblast homeostasis and inflammatory response

Maintenance of cell polarity and the structure of the apical surface of epithelial cells is a tightly regulated process necessary for tissue homeostasis. The syncytiotrophoblast of the human placenta is an entirely unique epithelial layer. It is a single giant multinucleate syncytial layer that comprises the maternal-facing surface of the human placenta. Like other epithelia, the syncytiotrophoblast is highly polarized with the apical surface dominated by microvillar membrane protrusions. Syncytiotrophoblast dysfunction is a key feature of pregnancy complications like preeclampsia. Preeclampsia is commonly associated with a heightened maternal immune response and pro-inflammatory environment. Importantly, reports have observed disruption of syncytiotrophoblast apical microvilli in placentas from preeclamptic pregnancies, indicating a loss of apical polarity, but little is known about how the syncytiotrophoblast regulates polarity. Here, we review the evolutionarily conserved mechanisms that regulate apical-basal polarization in epithelial cells, and the emerging evidence that PAR polarity complex components are critical regulators of syncytiotrophoblast homeostasis and apical membrane structure. Pro-inflammatory cytokines have been shown to disrupt the expression of polarity regulating proteins. We also discuss initial data showing that syncytiotrophoblast apical polarity can be disrupted by the addition of the pro-inflammatory cytokine tumor necrosis factor-α, revealing that physiologically relevant signals can modulate syncytiotrophoblast polarization. Since disrupted polarity is a feature of preeclampsia, further elucidation of the syncytiotrophoblast-specific polarity signaling network and testing whether the disruption of polarity-factor signaling networks may contribute to the development of preeclampsia is warranted.

Genome-Wide Analysis of Hypoxia-Inducible Factor Binding Reveals Targets Implicated in Impaired Human Placental Syncytiotrophoblast Formation under Low Oxygen

Preeclampsia (PE) is a common and serious complication of pregnancy with no cure except premature delivery. The root cause of PE is improper development of the placenta-the temporary organ supporting fetal growth and development. Continuous formation of the multinucleated syncytiotrophoblast (STB) layer via differentiation and fusion of cytotrophoblasts (CTBs) is vital for healthy placentation and is impaired in preeclamptic pregnancies. In PE, there is reduced/intermittent placental perfusion, likely resulting in a persistently low O2 environment. Low O2 inhibits differentiation and fusion of CTBs into STB and may thus contribute to PE pathogenesis; however, the underlying mechanisms are unknown. Because low O2 activates a transcription factor complex in cells known as the hypoxia-inducible factor (HIF), the objective of this study was to investigate whether HIF signaling inhibits STB formation by regulating genes required for this process. Culture of primary CTBs, the CTB-like cell line BeWo, and human trophoblast stem cells under low O2 reduced cell fusion and differentiation into STB. Knockdown of aryl hydrocarbon receptor nuclear translocator (a key component of the HIF complex) in BeWo cells restored syncytialization and expression of STB-associated genes under different O2 levels. Chromatin immunoprecipitation sequencing facilitated the identification of global aryl hydrocarbon receptor nuclear translocator/HIF binding sites, including several near genes implicated in STB development, such as ERVH48-1 and BHLHE40, providing new insights into mechanisms underlying pregnancy diseases linked to poor placental O2 supply.

Human placenta and trophoblasts simultaneously express three isoforms of atypical protein kinase-c

Atypical protein kinase-c (aPKC) isoforms are important regulators of polarity and stem cell differentiation. There are three isoforms of aPKC: aPKC-ι, aPKC-ζ, and PKM-ζ. Recently, aPKC-ι was shown to regulate human trophoblast stem cell (TSC) differentiation. Compensation by remaining isoforms when a single aPKC isoform is lost can occur, but the expression pattern of aPKC-ζ in placenta is unknown. Here we show that aPKC-ι, aPKC-ζ and a new isoform, aPKC-ζ III, are expressed in trophoblasts. Therefore, studies examining the role of aPKC isoforms that control for potential compensation between aPKC isoforms are necessary to understand aPKC-mediated regulation of TSC differentiation.

Digenic inheritance of mutations in EPHA2 and SLC26A4 in Pendred syndrome

Enlarged vestibular aqueduct (EVA) is one of the most commonly identified inner ear malformations in hearing loss patients including Pendred syndrome. While biallelic mutations of the SLC26A4 gene, encoding pendrin, causes non-syndromic hearing loss with EVA or Pendred syndrome, a considerable number of patients appear to carry mono-allelic mutation. This suggests faulty pendrin regulatory machinery results in hearing loss. Here we identify EPHA2 as another causative gene of Pendred syndrome with SLC26A4. EphA2 forms a protein complex with pendrin controlling pendrin localization, which is disrupted in some pathogenic forms of pendrin. Moreover, point mutations leading to amino acid substitution in the EPHA2 gene are identified from patients bearing mono-allelic mutation of SLC26A4. Ephrin-B2 binds to EphA2 triggering internalization with pendrin inducing EphA2 autophosphorylation weakly. The identified EphA2 mutants attenuate ephrin-B2- but not ephrin-A1-induced EphA2 internalization with pendrin. Our results uncover an unexpected role of the Eph/ephrin system in epithelial function.

While biallelic mutations of the SLC26A4 gene cause non-syndromic hearing loss with enlarged vestibular aqueducts or Pendred syndrome, a considerable number of patients carry mono-allelic mutations. Here the authors identify EPHA2 as another causative gene of Pendred syndrome with SLC26A4.

Regulation of programmed cell death ligand 1 expression by atypical protein kinase C lambda/iota in cutaneous angiosarcoma

The expression of immune checkpoint proteins such as programmed cell death protein 1 (PD‐1) and its ligand (PD‐L1) has been shown to correlate with patient prognosis in many malignant cancers. The expression of PD‐L1 is controlled by c‐Myc; however, further upstream regulation of PD‐L1 expression is largely unknown. We have previously shown that atypical protein kinase C lambda/iota (aPKCλ) phosphorylates the Forkhead box protein O1 (FoxO1) transcription factor at Ser218 to suppress its DNA‐binding ability, thereby regulating c‐Myc expression and controlling physiologic and pathologic endothelial proliferation. The presence of phosphorylation of FoxO1 at Ser218 (pSer218 FoxO1) in cutaneous angiosarcoma (CAS) strongly correlates with poor patient prognosis. Here, we reported that patients with PD‐L1⁺ cells in CAS lesions showed significantly worse prognosis compared to those that were PD‐L1⁻. Expression of PD‐L1 correlated with that of aPKCλ or the presence of pSer218FoxO1. Moreover, suppression of aPKCλ expression or inhibition of its activity in HUVECs or AS‐M, an established human angiosarcoma cell line, resulted in decreased PD‐L1 expression. Our results suggest that combined treatment with immune checkpoint inhibitors and aPKCλ inhibitors could be a novel treatment strategy for CAS patients.

PAR-3 controls endothelial planar polarity and vascular inflammation under laminar flow

Impaired cell polarity is a hallmark of diseased tissue. In the cardiovascular system, laminar blood flow induces endothelial planar cell polarity, represented by elongated cell shape and asymmetric distribution of intracellular organelles along the axis of blood flow. Disrupted endothelial planar polarity is considered to be pro-inflammatory, suggesting that the establishment of endothelial polarity elicits an anti-inflammatory response. However, a causative relationship between polarity and inflammatory responses has not been firmly established. Here, we find that a cell polarity protein, PAR-3, is an essential gatekeeper of GSK3β activity in response to laminar blood flow. We show that flow-induced spatial distribution of PAR-3/aPKCλ and aPKCλ/GSK3β complexes controls local GSK3β activity and thereby regulates endothelial planar polarity. The spatial information for GSK3β activation is essential for flow-dependent polarity to the flow axis, but is not necessary for flow-induced anti-inflammatory response. Our results shed light on a novel relationship between endothelial polarity and vascular homeostasis highlighting avenues for novel therapeutic strategies.

Caspase activation is not required for villous cytotrophoblast fusion into syncytiotrophoblasts

The villous trophoblast renews itself by fusion of individual stem cells (cytotrophoblasts, CT) with a functional syncytium (syncytiotrophoblast, ST). The literature indicates that fusion occurs with limited activation (proteolytic cleavage) of caspase-8 in CT and is inhibited either by blocking caspase-8 synthesis or inhibiting activation with a caspase-8-specific inhibitor, zIETD. We challenge part of this evidence: inhibition of differentiation with caspase-8 inhibitors. Br-cAMP-stimulated differentiation of isolated CT into multinucleated syncytia in culture is not blocked with three different low molecular weight inhibitors of caspase-8: broad caspase inhibitors zVAD-fmk and qVD-OPh and the caspase-8-specific inhibitor zIETD-fmk. Syncytialization was determined by desmoplakin staining of intracellular boundaries surrounding >2 nuclei and by diffusion within fused cells of long-lived cytoplasmic staining from half of original CT to the unstained half. Differentiation of isolated CT into hCGβ-secreting syncytiotrophoblast was also not blocked by the inhibitors nor was upregulation of hCGβ secretion blocked in ST-stripped and regenerated 5 day explant cultures. The ratio of CT to ST nuclei present was also not changed in explant cultures by caspase inhibitors. The effectiveness of caspase inhibitors was demonstrated by their ability to completely block TNFα-induced apoptosis. We conclude that activation of caspases in general, and caspase-8 in particular, is not required for villous CT differentiation into ST. However, another role of intact caspase-8 (proform) in CT differentiation remains possible.

The aetiology, clinical presentations and outcome of febrile encephalopathy in children in Papua New Guinea

BACKGROUND

Febrile encephalopathy, defined as fever, seizures and/or altered consciousness, is a common presentation in children in tropical developing countries. Outcomes range from complete recovery through varying degrees of neurological disability which slowly resolve or remain permanent to death from either the acute illness or complications. Whilst bacterial meningitis accounts for a proportion of children affected, the aetiology in many remains unclear but includes malaria and probably viral encephalitis.

AIM

To understand the aetiology, presentation and outcome of febrile encephalopathy in children in Papua New Guinea.

METHODS

Children aged between 1 month and 12 years presenting to Port Moresby General Hospital with febrile encephalopathy were studied prospectively. A detailed history and examination and the following laboratory investigations were undertaken as appropriate: cerebrospinal fluid (CSF) microscopy and bacterial culture, gram stain, measurement of protein and glucose and latex agglutination testing for Haemophilus influenzae, Streptococcus pneumoniae and Neisseria meningitides; Ziehl-Neelsen staining and india ink examination on selected samples; IgM for Japanese encephalitis, dengue, rubella and measles; PCR testing and mycobacterial culture for Mycobacterium tuberculosis. Blood was tested for flavivirus, measles and rubella IgM and IgG.

RESULTS

149 children were enrolled in the study. 129 had a lumbar puncture and CSF examination; 66 had a normal CSF white cell count. A clinical or laboratory-based diagnosis was possible for 140 children, but a definite pathogen was identifiable for only 55 (37%). The diagnoses included bacterial meningitis in 33 (S. pneumonia 16, H. influenza 13 and N. meningitides 4), tuberculous meningitis (5), probable tuberculous meningitis (18), malaria (10), cryptococcal meningitis (1), flavivirus encephalitis (5), rubella encephalitis (1), hepatic encephalopathy (1) and HIV encephalopathy (1). There were 28 cases of meningitis of unspecified aetiology. Of the five children with IgM-confirmed flavivirus encephalitis, one had dengue serotype 1 and two had Japanese encephalitis. Twenty-five children (including three of the five children with CSF flavivirus IgM) had serological IgG evidence of previous flavivirus infection. A history of multiple convulsions, the presence of neck stiffness and use of the Glasgow coma score (GCS) and TB score chart helped to identify children with bacterial meningitis and an adverse outcome and those with febrile convulsions.

CONCLUSION

The study confirms the importance of S. pneumonia and H. influenza as major causes of febrile encephalopathy in children in Papua New Guinea. Flaviviruses including Japanese encephalitis are a cause of the febrile encephalopathy syndrome, as is Mycobacterium tuberculosis. All children with febrile encephalopathy should have their GCS and TB scores recorded and should be examined for neck stiffness, and a history of the frequency of convulsions should be recorded. These basic clinical data can help to discriminate aetiology, to guide treatment and monitoring and to identify the children at highest risk of adverse outcome.

Alberta's new health research paradigms: Are graduate students being prepared for interdisciplinary team research?

Strategic prioritization of research agendas to address health problems with a large social and economic burden has increased the demand for interdisciplinary research. Universities have addressed the need for interdisciplinary research in their strategic documents. However, research training to equip graduates for careers in interdisciplinary research teams has not kept pace. We offer recommendations to graduate students, universities, health services organizations, and health research funders designed to increase the capacity for interdisciplinary research team training, and provide an example of an existing training program.

WHO criteria for measles elimination: a critique with reference to criteria for polio elimination

Smallpox was formally declared as eradicated in 1979. Smallpox is the only infectious disease of humans that has ever been eradicated. Poliomyelitis has been eliminated from three of the six World Health Organization (WHO) regions although not all countries within those regions always meet the elimination criteria. Elimination criteria for measles are being discussed. We use poliomyelitis and measles as examples to illustrate our assertion that the current approach to documenting measles elimination relies too heavily on criteria for surveillance quality, disadvantaging countries with long established and relatively inflexible surveillance systems. We propose an alternative approach to documenting measles elimination, with the two key criteria being molecular evidence to confirm the lack of a circulating endemic genotype for at least one year and maintenance of 95% coverage of one dose of measles-containing vaccine, with an opportunity for a second dose. Elimination status should be reviewed annually. We suggest four principles that should guide development of final criteria to document measles elimination: countries that have eliminated measles should be able to meet the elimination criteria; quality surveillance criteria are necessary but not sufficient to define elimination; quality surveillance criteria should be guided by elimination criteria, not the other way around; and elimination criteria should not differ between the WHO regions without good reason.

WHO criteria for measles elimination: a critique with reference to criteria for polio elimination

Smallpox was formally declared as eradicated in 1979. Smallpox is the only infectious disease of humans that has ever been eradicated. Poliomyelitis has been eliminated from three of the six World Health Organization (WHO) regions although not all countries within those regions always meet the elimination criteria. Elimination criteria for measles are being discussed. We use poliomyelitis and measles as examples to illustrate our assertion that the current approach to documenting measles elimination relies too heavily on criteria for surveillance quality, disadvantaging countries with long established and relatively inflexible surveillance systems. We propose an alternative approach to documenting measles elimination, with the two key criteria being molecular evidence to confirm the lack of a circulating endemic genotype for at least one year and maintenance of 95% coverage of one dose of measles-containing vaccine, with an opportunity for a second dose. Elimination status should be reviewed annually. We suggest four principles that should guide development of final criteria to document measles elimination: countries that have eliminated measles should be able to meet the elimination criteria; quality surveillance criteria are necessary but not sufficient to define elimination; quality surveillance criteria should be guided by elimination criteria, not the other way around; and elimination criteria should not differ between the WHO regions without good reason.

Serological profile of sporadic acute viral hepatitis in an area of hyper-endemic hepatitis B virus infection

BACKGROUND

Located in the south western part of Saudi Arabia, the Gizan region is largely a rural community in which hepatitis B and chronic liver disease including hepatocellular carcinoma are highly prevalent.

AIM OF STUDY

To determine the relative frequencies of acute hepatitis A, B, C and E in acute viral hepatitis in an area of hyperendemic hepatitis B infection.

METHODS AND MATERIALS

In a prospective study 246 consecutive patients (179 males and 67 females) diagnosed in a 2-year period were tested for markers of Hepatitis A virus (HAV), hepatitis B virus (HBV), hepatitis C (HCV) and hepatitis E virus (HEV).

RESULTS

Of the patients tested, 131 (53.3%) were children ( < 10 years), and 42 (17%) were 11 - 20 years in age. Ig M anti -HAV, IgM anti-HBV, anti- HCV and IgM anti-HEV were positive in 37%, 19.1%, 3.7% and 13.7% respectively. Markers of these viruses were absent in 24.4%. Among 131 children (< 10 years) the commonest cause of AVH was HAV occurring in 57.3% of the cases. In adults (> 21 years) HBV was found in 35.6% and IgM anti -HAV was detected in only 6.8%. In contrast to the age- related decline in the frequency of acute HA, the proportion of acute HE were similar in all age groups (13.7% in children, 16.7% in adolescents and 11.0% in adults).

CONCLUSION

The study indicated that HAV is still a common cause of AVH particularly among children in Gizan. Acute 1-113 had a low occurrence among the children, evidently as a consequence of the integration of HB vaccine into the Saudi Arabian national EPI, 10 years ago. With the availability of combined HB and HA vaccines, It should be possible to graft the vaccination against HAV on to the existing program in Saudi Arabia. Affecting 13.4% of the group studied, sporadic HEV constitute a significant cause of AVH in this population. Until HEV vaccine becomes widely available, its prevention would be mainly by the improvement of socio - economic and hygienic standards of the population.

Perception of social value predicts participation in school-based research

OBJECTIVE

To investigate factors affecting the participation of schools in a serosurvey.

METHODS

A telephone interview was conducted with a representative of 80 schools (response rate 92%). The schools had been randomly selected to participate in a seroprevalence survey evaluating a measles vaccination campaign of Victorian school-aged children in 1998.

RESULTS

Univariate analysis suggested that responses to the interview were not influenced by school level (primary/secondary), geographic location, funding source or participation in the seroprevalence survey. There was, however, a strong association of participation in the seroprevalence survey with the perception of value to students and the value to the community. Factor analysis identified two issues: the societal value and practical issues, which explained most of the variance in participation (pseudo R2 = 0.84).

CONCLUSION

The perception of the benefits of the study strongly influenced the decision by school representatives to participate in the seroprevalence survey.

IMPLICATIONS

Recruitment of schools for health-related research may be improved if the number of research projects in schools is monitored and possibly restricted, and the social value of the research is emphasised.

ELISA for IgG-class antibody to hepatitis E virus based on a highly conserved, conformational epitope expressed in Escherichia coli

In assays based on most recombinant hepatitis E virus (HEV) antigens, the IgG antibody responses to HEV are observed commonly to wane or disappear after the acute phase of infection. Such IgG assays have therefore been used for the diagnosis of acute HEV infection, but they have limited usefulness in seroepidemiological studies. Using western immunoblotting, it was shown previously that the open reading frame (ORF) 2.1 antigen, representing the carboxy-terminal 267 amino acids (aa) of the capsid protein, exposes a conformational epitope which allows optimal detection of convalescent antibody compared to other proteins expressed in Escherichia coli. This conformational epitope is shown to be highly conserved between divergent human HEV isolates, and the development of a sensitive and highly specific enzyme immunoassay (ELISA) based on this recombinant antigen is described. The ORF2.1 ELISA allows the detection and quantitation of both acute- and convalescent phase HEV-specific IgG, and will help to define better the antibody responses to the virus and the prevalence of HEV infection worldwide.

Washing and trypsin treatment of in vitro derived bovine embryos exposed to bovine viral diarrhea virus

Gametes, somatic cells and materials of animal origin in media are potential sources for introducing bovine viral diarrhea virus (BVDV) into systems for production of IVF bovine embryos. Further, the efficacy of washing and trypsin treatment for removal of BVDV from IVF embryos is questionable. Washing and trypsin treatments recommended by the International Embryo Transfer Society for in vivo-derived embryos were applied to in vitro-derived, virus-exposed, bovine embryos in this side-by-side comparison of treatments. Embryos for the study were produced in a virus-free system in which follicular oocytes were matured and fertilized in vitro and presumptive zygotes were co-cultured with bovine uterine tubal cells for 7 d. A total of 18 trials was performed, 9 using a noncytopathic BVDV and 9 using a cytopathic BVDV. In each trial, 4 equal groups of 10 or less, zona pellucida-intact embryos/ova were assembled, including 2 groups of morulae and blastocysts (M/B) and 2 groups of nonfertile or degenerated ova (NFD). Each group was prewashed and exposed to 10(4) to 10(6) TCID50/mL of either noncytopathic (SD-1) or cytopathic (NADL) BVDV for 2 h. Following in vitro viral exposure, one group of M/B and one group of NFD were washed. The other groups of M/B and NFD were trypsin-treated. Both treatments were consistent with IETS guidelines. After in vitro exposure to noncytopathic BVDV and washing, viral assays of 100% (9/9) and 78% (7/9) of the groups of M/B and NFD ova, respectively, were positive. After in vitro exposure to cytopathic BVDV and washing, viral assay of 33% (3/9) of the groups of both M/B and NFD ova were positive. After in vitro exposure to noncytopathic BVDV and trypsin treatment, viral assay of 44% (4/9) of groups of M/B and 67% (6/9) of groups of NFD ova were positive. Finally, after in vitro exposure to cytopathic BVDV and trypsin treatment, viral assay of 22% (2/9) of the groups of M/B and 44% (4/9) of the groups of NFD ova were positive. Contingency table analysis, in which data was stratified by embryo type and virus biotype, was used to compare results. While a difference existed between results of the 2 treatments of groups of M/B within the noncytopathic biotype (P = 0.01, Mantel Haenszel Chi-square), no difference was observed between comparison of treatment between all groups in both biotypes (P > 0.05).

Climate-related corrections for improved estimation of energy expenditure from heart rate in children

The purpose of this study was to determine the relationship between children's heart rate (HR) and climatic heat stress at several O2 uptake (Vo2) levels and to construct equations and nomograms for an improved estimation of energy expenditure (EE) from HR monitoring. On four occasions 12 boys and 8 girls (8-11 yr) cycled for 5 min each at 35, 55, and 75% of peak Vo2 (random order), with rest periods in between, in a climatic chamber. The randomly assigned conditions were 22 degrees C dry bulb temperature, 50% relative humidity (RH); 28 degrees C, 55% RH; 32 degrees C, 52% RH; or 35 degrees C, 58% RH. HR and Vo2 were determined during the final 2 min of rest and exercise bouts. HR measured at a dry bulb temperature (T) (HRmeas) was then related to a HR at 22 degrees C that would have been expected to occur at an identical Vo2 (HRcalc22) by using individual 22 degrees C HR-Vo2 regression lines. HRcalc22 could be estimated from HRmeas.[1.175032-(0.007956.T)], with a mean error of prediction for the entire group < 1.5 beats/min for each temperature. The following conclusions were drawn: 1) children's HR at a given Vo2 increases linearly with ambient temperature at 22-35 degrees C, 50-60% RH; and 2) HR can be corrected for the influence of climate in groups of children resting and exercising at the above conditions, thereby reducing the error of estimating EE from HR.