Quantitative Viral Outgrowth Assay to Measure the Functional SIV Reservoir in Myeloid Cells

The role of CD4+ T cells in HIV infection and the latent reservoir, that is, latently infected cells that harbor replication competent virus, has been rigorously assessed. We have previously reported a quantitative viral outgrowth assay (QVOA) for SIV that demonstrated the frequency of latently infected CD4+ T cells is approximately 1 in a million cells, similar to that of HIV infected individuals on ART. However, the frequency of productively infected monocytes in blood and macrophages in tissues has not been similarly studied. Myeloid cells are infected during acute HIV and SIV infection; however, unlike lymphocytes, they are resistant to the cytopathic effects of the virus. Moreover, tissue-resident macrophages have the ability to self-renew and persist in the body for months to years. Thus, tissue macrophages, once infected, have the characteristics of a stable viral reservoir. A better understanding of the number of productively infected macrophages is critical to understanding the role of infected myeloid cells as a viral reservoir. In order to assess the functional latent reservoir. we have developed specific QVOAs for monocytes in blood, and macrophages in spleen, BAL and brain, which are described in detail in this chapter.

Predictors of patient and system delay for primary percutaneous coronary intervention

Background

The delay times of the patient and the system for primary percutaneous coronary intervention (p-PCI) have a determining impact on the prognosis of patients with acute myocardial infarction with ST segment elevation (STEMI).

Purpose

To identify the predictors of patient and system delay for p-PCI in the period of 2020 at a reference hospital for p-PCI.

Methods

Patients submitted to p-PCI in the period from March to September 2020 were included and compared with the same period in 2019. We analyzed the differences between the two groups regarding the patient's delay times, time from the onset of symptoms to the first medical contact (FCM) and the system (time from the first contact with the health system to p-ICP). Data collection of the patient's previous history, coronary intervention performed and post-PCI follow-up was performed using the electronic patient record. Univariate analysis and logistic regression models from multivariate analysis were used to determine the predictors of “patient delay” and “system delay” and adjusted for confounding factors. The analysis was performed with a significance level of 5%.

Results

We included in the study 255 patients who underwent p-PCI, of which 122 in the period from 2020 and 133 in the period from 2019. Regarding the characteristics of the population, there were no significant differences between the two periods. Regarding the patient's delay time, there were no statistically significant differences. The variable first medical contact with a non p-PCI center was the only variable associated with system delay>90 minutes in the multivariate analysis, OR (6.18: 95% CI, 1.91–20), p=0.002. There was a statistically significant association between the period of 2020 (pandemic period) and total ischemia time, but with a negative effect, dependent variable adjusted for confounding factors [adjusted OR: −0.10; 95% CI: −107.61 to −5.57; p=0.03].

Conclusion

In this study, the patient's admission to a non p-PCI centers was identified as the only predictor of longer delay until p-PCI (system delay). However, these results should serve as a contribution to decision making in order to mitigate risks, regardless of any associated catastrophe and eventually alert the population not to neglect the symptoms suspected of acute myocardial infarction.

Funding Acknowledgement

Type of funding sources: None.

Clarifying the Cryptic Host Specificity of Blastocystis spp. Isolates from Alouatta palliata and A. pigra Howler Monkeys

Although the presence of cryptic host specificity has been documented in Blastocystis, differences in infection rates and high genetic polymorphism within and between populations of some subtypes (ST) have impeded the clarification of the generalist or specialist specificity of this parasite. We assessed the genetic variability and host specificity of Blastocystis spp. in wild howler monkeys from two rainforest areas in the southeastern region of Mexico. Fecal samples of 225 Alouatta palliata (59) and A. pigra (166) monkeys, belonging to 16 sylvatic sites, were analyzed for infection with Blastocystis ST using a region of the small subunit rDNA (SSUrDNA) gene as a marker. Phylogenetic and genetic diversity analyses were performed according to the geographic areas where the monkeys were found. Blastocystis ST2 was the most abundant (91.9%), followed by ST1 and ST8 with 4.6% and 3.5%, respectively; no association between Blastocystis ST and Alouatta species was observed. SSUrDNA sequences in GenBank from human and non-human primates (NHP) were used as ST references and included in population analyses. The haplotype network trees exhibited different distributions: ST1 showed a generalist profile since several haplotypes from different animals were homogeneously distributed with few mutational changes. For ST2, a major dispersion center grouped the Mexican samples, and high mutational differences were observed between NHP. Furthermore, nucleotide and haplotype diversity values, as well as migration and genetic differentiation indexes, showed contrasting values for ST1 and ST2. These data suggest that ST1 populations are only minimally differentiated, while ST2 populations in humans are highly differentiated from those of NHP. The host generalist and specialist specificities exhibited by ST1 and ST2 Blastocystis populations indicate distinct adaptation processes. Because ST1 exhibits a generalist profile, this haplotype can be considered a metapopulation; in contrast, ST2 exists as a set of local populations with preferences for either humans or NHP.

Evidence for a geographical cline of casein haplotypes in Portuguese cattle breeds

Genetic variants of bovine milk proteins have been intensively used to characterize breeds and as markers for population/QTL studies throughout the world. However, a large number of cattle breeds including those found in Portugal, remain unstudied. In this work, we have analysed the genetic variation of six milk protein loci in 10 Portuguese cattle breeds by isoelectric focusing. High genetic diversities were generally found across breeds, with the exception of Mirandesa that showed a trend to fixation of the most common alleles in five loci, as well as of the rarer CSN3B allele. The casein haplotype BA2A was often the most frequent, followed by haplotypes BA2B and BA1A. Remarkably, CA2A was found to be the second most frequent haplotype in Southern breeds, supporting a geographical cline between Central-Northern European breeds and Bos indicus populations. Our data suggest that high genetic similarity among neighbouring Portuguese breeds is mainly caused by gene flow, and that the geographical distribution of particular casein haplotypes may indicate an influence of African cattle.

Heterodimerization of calcium sensing receptors with metabotropic glutamate receptors in neurons

Calcium sensing (CaR) and Group I metabotropic glutamate receptors exhibit overlapping expression patterns in brain, and share common signal transduction pathways. To determine whether CaR and Group I metabotropic glutamate receptors (mGluRs) (mGluR1alpha and mGluR5) can form heterodimers, we immunoprecipitated CaR from bovine brain and observed co-precipitation of mGluR1alpha. CaR and mGluR1alpha co-localize in hippocampal and cerebellar neurons, but are expressed separately in other brain regions. In vitro transfection studies in HEK-293 cells established the specificity and disulfide-linked nature of the CaR:mGluR1alpha (CaR:mGluR5) interactions. CaR:mGluR1alpha (CaR:mGluR5) heterodimers exhibit altered trafficking via Homer 1c when compared with CaR:CaR homodimers. CaR becomes sensitive to glutamate-mediated internalization when present in CaR:mGluR1alpha heterodimers. These results demonstrate cross-family covalent heterodimerization of CaR with Group I mGluRs, and increase the potential role(s) for CaR in modulating neuronal function.

Calcium-sensing receptor activation induces intracellular calcium oscillations

Parathyroid hormone secretion is exquisitely sensitive to small changes in serum Ca2+concentration, and these responses are transduced via the Ca2+-sensing receptor (CaR). We utilized heterologous expression in HEK-293 cells to determine the effects of small, physiologically relevant perturbations in extracellular Ca2+ on CaR signaling via phosphatidylinositol-phospholipase C, using changes in fura 2 fluorescence to quantify intracellular Ca2+. Chronic exposure of CaR-transfected cells to Ca2+ in the range from 0.5 to 3 mM modulated the resting intracellular Ca2+concentration and the subsequent cellular responses to acute extracellular Ca2+ perturbations but had no effect on thapsigargin-sensitive Ca2+ stores. Modest, physiologically relevant increases in extracellular Ca2+concentration (0.5 mM increments) caused sustained (30–40 min) low-frequency oscillations of intracellular Ca2+ (∼45 s peak to peak interval). Oscillations were eliminated by 1 μM thapsigargin but were insensitive to protein kinase inhibitors (staurosporine, KN-93, or bisindolylmaleimide I). Staurosporine did increase the fraction of cells oscillating at a given extracellular Ca2+ concentration. Serum Ca2+ concentrations thus chronically regulate cells expressing CaR, and small perturbations in extracellular Ca2+ alter both resting intracellular Ca2+ as well as Ca2+ dynamics.

Dimerization of the calcium-sensing receptor occurs within the extracellular domain and is eliminated by Cys --> Ser mutations at Cys101 and Cys236

Calcium-sensing receptors are present in membranes as dimers that can be reduced to monomers with sufhydryl reagents. All studies were carried out on the human calcium-sensing receptor tagged at the carboxyl terminus with green fluorescent protein (hCaR-GFP) to permit identification and localization of expressed proteins. Truncations containing either the extracellular agonist binding domain plus transmembrane helix 1 (ECD/TMH1-GFP) or the transmembrane domain plus the intracellular carboxyl terminus (TMD/carboxyl terminus-GFP) were used to identify the dimerization domain. ECD/TMH1-GFP was a dimer in the absence of reducing reagents, whereas TMD/carboxyl-terminal GFP was a monomer in the absence or presence of reducing agents, suggesting that dimerization occurs via the ECD. To identify the residue(s) involved in dimerization within the ECD, cysteine --> serine point mutations were made in residues that are conserved between hCaR and metabotropic glutamate receptors. Mutations at positions 60 and 131 were expressed at levels comparable to wild type in HEK 293 cells, had minimal effects on hCaR function, and did not eliminate dimerization, whereas mutations at positions 101 and 236 greatly decreased receptor expression and resulted in significant amounts of monomer in the absence of reducing agents. The double point mutant hCaR(C101S/C236S)-GFP was expressed more robustly than either C101S or C236S and covalent dimerization was eliminated. hCaR(C101S/C236S)-GFP had a decreased affinity for extracellular Ca2+ and slower response kinetics upon increases or decreases in agonist concentration. These results suggest that covalent, disulfide bond-mediated dimerization of the calcium-sensing receptor contributes to stabilization of the ECD and to acceleration of the transitions between inactive and active receptor conformations.

A carboxyl-terminal domain controls the cooperativity for extracellular Ca2+ activation of the human calcium sensing receptor. A study with receptor-green fluorescent protein fusions

Calcium sensing receptors are part of a growing G protein-coupled receptor family, which includes metabotropic glutamate, gamma-aminoisobutyric acid, and pheromone receptors. The distinctive structural features of this family include large extracellular domains that bind agonist and large intracellular, carboxyl-terminal domains of as yet undefined function(s). We have explored the contribution(s) of the carboxyl terminus of the human calcium sensing receptor (CaR) by assessing extracellular Ca2+-mediated changes in intracellular Ca2+ in individual HEK-293 cells transfected with CaR clones. In-frame fusion of EGFP to the carboxyl terminus of CaR had no effect on either the dose response for extracellular Ca2+ activation or CaR desensitization. Carboxyl-terminal truncations, fused in-frame with EGFP (CaRDelta1024-EGFP, CaRDelta908-EGFP, CaRDelta886-EGFP, and CaRDelta868-EGFP), were assessed for alterations in Ca2+-dependent activation or desensitization. Significant effects on the dose-response relation for extracellular Ca2+ were observed only for the CaRDelta868 truncation, which exhibited a decreased affinity for extracellular Ca2+ and a decrease in the apparent cooperativity for Ca2+-dependent activation. The alterations in extracellular Ca2+ affinity and cooperativity observed with CaRDelta868 were recapitulated by a point mutation, T876D, in the full-length CaR-EGFP background. All truncations with wild type dose-response relations exhibited desensitization time courses that were comparable to the full-length CaR, whereas the CaRDelta868 receptor desensitized completely after two exposures to 10 mM Ca2+. Interestingly, the CaR point mutation T876D exhibited desensitization comparable to wild type CaR, suggesting that this mutation specifically modifies CaR cooperativity. In conclusion, these studies suggest that amino acid residues between 868 and 886 are critical to the apparent cooperativity of Ca2+-mediated activation of G proteins and to CaR desensitization.

Ca2+-sensing receptors in intestinal epithelium

Expression of Ca2+-sensing receptors (CaR) was demonstrated in several human intestinal epithelial cell lines (T84, HT-29, and Caco-2) and in rat intestinal epithelium by both reverse transcriptase-polymerase chain reaction (PCR) and Northern blotting of RNA. Restriction patterns of the PCR products were of the sizes predicted by the human and rat sequences. CaR agonists (Ca2+, poly-L-arginine, protamine) mediated an increase in intracellular Ca2+ in HT-29-18-C1 cells (monitored by changes in fura 2 fluorescence), which was dependent on release from thapsigargin-sensitive stores. U-73122, an inhibitor of phosphatidylinositol-phospholipase C, eliminated the CaR agonist-mediated rise in intracellular Ca2+, whereas its inactive analog, U-73343, had no effect. Pertussis toxin pretreatment had no effect on CaR agonist-mediated modulation of intracellular Ca2+. Taken together, these studies demonstrate that CaR are expressed in intestinal epithelial cells and couple to mobilization of intracellular Ca2+. The presence of CaR in intestinal epithelial cells presents a new locus for investigations into the role(s) of extracellular Ca2+ in modulating intestinal epithelial cell differentiation and transepithelial Ca2+ transport.