Identification of residues in the first transmembrane domain of the P2X7 that regulates receptor trafficking, sensitization, and dye uptake function.

P2X receptors (P2X1-7) are trimeric ion channels activated by extracellular ATP. Each P2X subunit contains two transmembrane helices (TM1 and TM2). We substituted all residues in TM1 of rat P2X7 with alanine or leucine one by one, expressed mutants in HEK293T cells, and examined the pore permeability by recording both membrane currents and fluorescent dye uptake in response to agonist application. Alanine substitution of G27, K30, H34, Y40, F43, L45, M46, and D48 inhibited agonist-stimulated membrane current and dye uptake, and all but one substitution, D48A, prevented surface expression. Mutation V41A partially reduced both membrane current and dye uptake, while W31A and A44L showed reduced dye uptake not accompanied by reduced membrane current. Mutations T28A, I29A, and L33A showed small changes in agonist sensitivity, but they had no or small impact on dye uptake function. Replacing charged residues with residues of the same charge (K30R, H34K, and D48E) rescued receptor function, while replacement with residues of opposite charge inhibited (K30E and H34E) or potentiated (D48K) receptor function. Prolonged stimulation with agonist-induced current facilitation and a leftward shift in the dose-response curve in the P2X7 wild-type and most functional mutants, but sensitization was absent in the W31A, L33A, and A44L. Detailed analysis of the decay of responses revealed two kinetically distinct mechanisms of P2X7 deactivation: fast represents agonist unbinding, and slow might represent resetting of the receptor to the resting closed state. These results indicate that conserved and receptor-specific TM1 residues control surface expression of the P2X7 protein, non-polar residues control receptor sensitization, and D48 regulates intrinsic channel properties.

Intestinal mycobiome associated with diagnosis of inflammatory bowel disease based on tissue biopsies.

Analysis of mycobiome from formalin-fixed, paraffin-embedded (FFPE) biopsies should preferentially detect only fungi which are actually present in the intestine wall, in contrast to stool samples, which are limited by the diet composition. Next generation sequencing provides the advantage of analyzing many species from a single sample. Consequently, canonical correspondence analysis divided fungal genera present in FFPE intestinal tissues into three well-defined experimental groups (negative controls - NC, Crohn's disease - CD, ulcerative colitis - UC). Simultaneously, the analysis showed that particular fungal genera are associated with these experimental groups and several fungal genera occurred in all experimental groups equally. Our results also showed a noticeable increase of Ascomycota proportion from NC, through CD to UC. Fungal genera Malassezia, Cladosporium and Toninia occurred in all experimental groups assuming that they are common components of the intestinal mycobiome. Other fungal genera found only in the NC experimental group were non-pathogenic and might bring some benefits. In contrast, CD and UC samples were characterized by an accumulation of genera with inhibitive effects on growth of other fungal genera and the presence of opportunistic pathogens. Furthermore, a decrease in the fungal genus Malassezia in inflammatory tissues was observed; Specifically, the UC experimental group showed a connection between the presence of Candida and seven time's lower amounts of Malassezia (compared to amounts found in NC). The CD experimental group was characterized by the simultaneous presence of Engyodontium album with Lecanicillium, and indicates a possible pathogenic effect of Ramularia in disease development. LAY SUMMARY: Mycobiome analysis of formalin-fixed and paraffin-embedded biopsies may highlight actual fungal genera composition in the intestinal wall. Interestingly, experimental groups of Crohn's disease and ulcerative colitis clearly differed by structure of their mycobiomes.