Lack of evidence for functional luteinising hormone chorionic gonadotropin receptors in non-pregnant human endometrial stromal cells

The human luteinising hormone chorionic gonadotropin receptor (LHCGR) is a G-protein coupled receptor activated by both human chorionic gonadotropin (hCG) and luteinizing hormone (LH), two structurally related gonadotropins with essential roles in ovulation and maintenance of the corpus luteum. LHCGR expression predominates in ovarian tissues where it elicits functional responses through cyclic adenosine mononucleotide (cAMP), Ca2+ and extracellular signal-regulated kinase (ERK) signalling. LHCGR has also been localized to the human endometrium, with purported roles in decidualization and implantation. However, these observations are contentious. In this investigation, transcripts encoding LHCGR were undetectable in bulk RNA sequencing datasets from whole cycling endometrial tissue and cultured human endometrial stromal cells (EnSC). However, analysis of single-cell RNA sequencing data revealed cell-to-cell transcriptional heterogeneity and identified a small subpopulation of stromal cells with discernible LHCGR transcripts. In HEK-293 cells expressing recombinant LHCGR, both hCG and LH elicited robust cAMP, Ca2+ and ERK signals that were absent in wild type HEK-293 cells. However, none of these responses were recapitulated in primary EnSC cultures. In addition, proliferation, viability and decidual transformation of EnSC were refractory to both hCG and LH, irrespective of treatment to induce differentiation. Although we challenge the assertion that LHCGR is expressed at a functionally active level in the human endometrium, the discovery of a discrete subpopulation of EnSC that express LHCGR transcripts may plausibly account for the conflicting evidence in the literature.

CNNM proteins selectively bind to the TRPM7 channel to stimulate divalent cation entry into cells

Magnesium is essential for cellular life, but how it is homeostatically controlled still remains poorly understood. Here, we report that members of CNNM family, which have been controversially implicated in both cellular Mg2+ influx and efflux, selectively bind to the TRPM7 channel to stimulate divalent cation entry into cells. Coexpression of CNNMs with the channel markedly increased uptake of divalent cations, which is prevented by an inactivating mutation to the channel’s pore. Knockout (KO) of Trpm7 in cells or application of the TRPM7 channel inhibitor NS8593 also interfered with CNNM-stimulated divalent cation uptake. Conversely, KO of CNNM3 and CNNM4 in HEK-293 cells significantly reduced TRPM7-mediated divalent cation entry, without affecting TRPM7 protein expression or its cell surface levels. Furthermore, we found that cellular overexpression of phosphatases of regenerating liver (PRLs), known CNNMs binding partners, stimulated TRPM7-dependent divalent cation entry and that CNNMs were required for this activity. Whole-cell electrophysiological recordings demonstrated that deletion of CNNM3 and CNNM4 from HEK-293 cells interfered with heterologously expressed and native TRPM7 channel function. We conclude that CNNMs employ the TRPM7 channel to mediate divalent cation influx and that CNNMs also possess separate TRPM7-independent Mg2+ efflux activities that contribute to CNNMs’ control of cellular Mg2+ homeostasis.

Investigating the Effect of Kappa Opioid Receptor Agonists on Serotonin Transporter Function in HEK-293 Cells

<p>The serotonin (5-HT) transporter (SERT) and the kappa opioid receptor (KOPr) are important brain proteins. Currently, it is known that KOPr modulates 5-HT concentrations but the biochemical mechanisms responsible remain enigmatic. The 5-HT and KOPr relationship is thought to involve SERT because both SERT and KOPr co-localise in the dorsal raphe nucleus (DRN), a brain region involved in drug addiction, affective disorders, and stress homeostasis. Thus, elucidating the KOPr and SERT relationship will clarify biomedical targets for these disorders. To investigate this relationship the effect of KOPr activation on SERT function was examined in HEK-293 cells co-expressing myc-rKOPr and eGFP-tagged hSERT. We found the KOPr agonists U50,488H, Salvinorin A (Sal A) and DS-3-240 had no acute (5 min) effect on SERT function as measured by rotating disc electrode voltammetry (RDEV) incubated with 1’-diethyl-2,2’-cyanine iodide (D-22; 1.5 mM) and by confocal microscopy. Interestingly, SERT function significantly decreased with chronic (30 min) exposure to U50,488H (**p<0.01) and Sal A (**p<0.01) as measured with a novel high-throughput assay; this decrease was also attenuated with 5 min pre-treatment of the SERT inhibitor, fluoxitene (***p<0.001). Furthermore, this novel high-throughput assay also replicated our laboratories recent finding that chronic (30 min) exposure to U50,488H (**p<0.01) and Sal A (**p<0.01) significantly increase dopamine transporter (DAT) function in HEK-293 cells co-expressing myc-rKOPr and eYFP-tagged DAT. Collectively, these findings suggest in this cell model that chronic (30 min) KOPr activation by U50,488H and Sal A decreases SERT function.</p>

Investigating the Effect of Kappa Opioid Receptor Agonists on Serotonin Transporter Function in HEK-293 Cells

<p>The serotonin (5-HT) transporter (SERT) and the kappa opioid receptor (KOPr) are important brain proteins. Currently, it is known that KOPr modulates 5-HT concentrations but the biochemical mechanisms responsible remain enigmatic. The 5-HT and KOPr relationship is thought to involve SERT because both SERT and KOPr co-localise in the dorsal raphe nucleus (DRN), a brain region involved in drug addiction, affective disorders, and stress homeostasis. Thus, elucidating the KOPr and SERT relationship will clarify biomedical targets for these disorders. To investigate this relationship the effect of KOPr activation on SERT function was examined in HEK-293 cells co-expressing myc-rKOPr and eGFP-tagged hSERT. We found the KOPr agonists U50,488H, Salvinorin A (Sal A) and DS-3-240 had no acute (5 min) effect on SERT function as measured by rotating disc electrode voltammetry (RDEV) incubated with 1’-diethyl-2,2’-cyanine iodide (D-22; 1.5 mM) and by confocal microscopy. Interestingly, SERT function significantly decreased with chronic (30 min) exposure to U50,488H (**p<0.01) and Sal A (**p<0.01) as measured with a novel high-throughput assay; this decrease was also attenuated with 5 min pre-treatment of the SERT inhibitor, fluoxitene (***p<0.001). Furthermore, this novel high-throughput assay also replicated our laboratories recent finding that chronic (30 min) exposure to U50,488H (**p<0.01) and Sal A (**p<0.01) significantly increase dopamine transporter (DAT) function in HEK-293 cells co-expressing myc-rKOPr and eYFP-tagged DAT. Collectively, these findings suggest in this cell model that chronic (30 min) KOPr activation by U50,488H and Sal A decreases SERT function.</p>

Direct addition of poly-lysine or poly-ethylenimine to the medium, a simple alternative to plate pre-coating

For most cell culture experiments, it is indispensable that the cells are firmly anchored to the culture plates, tolerating several rinsing steps, and withstanding shear forces or temperature changes without detaching. For semi-adherent cells such as the very common HEK 293 cells, this could so far be obtained only by time-consuming plate pre-coating with cationic polymer solutions. We report here, that i) pre-coating with the cheaper poly-ethylenimine (PEI) works as well as the commonly used poly-D-lysine (PDL), but more importantly and novel ii) that simple direct addition of either PEI (1.5 µg/ml) or PDL (2 µg/ml) to the cell culture medium results in strongly anchored HEK 293 cells, indistinguishable from ones seeded on pre-coated plates. Therefore, the replacement of plate pre-coating by direct addition of either PEI or PDL gives comparable excellent results, but is highly labour-, time-, and cost-efficient. Interestingly, additional experiments in this context showed that strong cell attachment requires only cationic polymers but not fetal calf serum added to the medium. Fetal calf serum is, however, of course required for further maintenance and growth of the cells.

Beyond Ca2+ signalling: the role of TRPV3 in the transport of NH4+

Mutations of TRPV3 lead to severe dermal hyperkeratosis in Olmsted syndrome, but whether the mutants are trafficked to the cell membrane or not is controversial. Even less is known about TRPV3 function in intestinal epithelia, although research on ruminants and pigs suggests an involvement in the uptake of NH4+. It was the purpose of this study to measure the permeability of the human homologue (hTRPV3) to NH4+, to localize hTRPV3 in human skin equivalents, and to investigate trafficking of the Olmsted mutant G573S. Immunoblotting and immunostaining verified the successful expression of hTRPV3 in HEK-293 cells and Xenopus oocytes with trafficking to the cell membrane. Human skin equivalents showed distinct staining of the apical membrane of the top layer of keratinocytes with cytosolic staining in the middle layers. Experiments with pH-sensitive microelectrodes on Xenopus oocytes demonstrated that acidification by NH4+ was significantly greater when hTRPV3 was expressed. Single-channel measurements showed larger conductances in overexpressing Xenopus oocytes than in controls. In whole-cell experiments on HEK-293 cells, both enantiomers of menthol stimulated influx of NH4+ in hTRPV3 expressing cells, but not in controls. Expression of the mutant G573S greatly reduced cell viability with partial rescue via ruthenium red. Immunofluorescence confirmed cytosolic expression, with membrane staining observed in a very small number of cells. We suggest that expression of TRPV3 by epithelia may have implications not just for Ca2+ signalling, but also for nitrogen metabolism. Models suggesting how influx of NH4+ via TRPV3 might stimulate skin cornification or intestinal NH4+ transport are discussed.

Increase of 5-HT levels is induced both in mouse brain and HEK-293 cells following their exposure to a non-viral tryptophan hydroxylase construct

Tryptophan hydroxylase type 2 (Tph2) is the rate-limiting enzyme for serotonin (5-HT) biosynthesis in the brain. Dysfunctional Tph2 alters 5-HT biosynthesis, leading to a deficiency of 5-HT, which could have repercussions on human behavior. In the last decade, several studies have associated polymorphisms of the TPH2 gene with suicidal behavior. Additionally, a 5-HT deficiency has been implicated in various psychiatric pathologies, including alcoholism, impulsive behavior, anxiety, and depression. Therefore, the TPH2 gene could be an ideal target for analyzing the effects of a 5-HT deficiency on brain function. The aim of this study was to use the construct pIRES-hrGFP-1a-Tph2-FLAG to treat CD1-male mice and to transfect HEK-293-cells and then to evaluate whether this treatment increases 5-HT production. 5-HT levels were enhanced 48 h post-transfection, in HEK-293 cells. Three days after the ocular administration of pIRES-hrGFP-1a-Tph2-FLAG to mice, putative 5-HT production was significantly higher than in the control in both hypothalamus and amygdala, but not in the brainstem. Further research will be needed on the possible application of this treatment for psychiatric diseases involving a Tph2 dysfunction or serotonin deficiency.