Síndrome do Intestino Irritável, microbiota e as suas interrelações com as perturbações mentais : uma revisão narrativa

Trabalho Final do Curso de Mestrado Integrado em Medicina, Faculdade de Medicina, Universidade de Lisboa, 2022Todos os animais, incluindo os humanos, desenvolveram associações com comunidades microbianas. Estas coleções de microrganismos, coletivamente designadas por microbiota, habitam as superfícies corporais ambientalmente expostas, com a comunidade do trato gastrointestinal a representar a coleção de microrganismos de maior densidade no corpo humano. O organismo humano estabelece uma relação dinâmica com a microbiota entérica e essa interação é essencial à homeostasia pois estados de disbiose favorecem o aparecimento de patologias gastrointestinais. Entre estas destaca-se o Síndrome do Intestino Irritável, uma doença funcional do sistema gastrointestinal caracterizada por dor, distensão abdominal e alterações da motilidade, e que tem sido associada a elevada prevalência de perturbações do foro psiquiátrico. Neste trabalho temos como objetivo realizar uma revisão bibliográfica, recorrendo ao motor de busca Pubmed, que nos permita caracterizar as funções da microbiota intestinal, compreender a influência da microbiota intestinal na etiologia da Síndrome do Intestino Irritável e abordar a relação entre a Síndrome do Intestino Irritável e a doença psiquiátrica. Deste trabalho resulta a demonstração da existência de interações entre hospedeiros e as suas comunidades bacterianas residentes na formação e função de sistemas neurológicos. Estas relações, que envolvem intrincadas vias de sinalização químicas e imunológicas, desempenham um papel na saúde e na forma como entendemos a doença neurológica. Outrora percecionada por defeitos em processos cerebrais, a doença mental está hoje distante da perspetiva centrada exclusivamente no cérebro. Na verdade, o cérebro e o intestino comunicam, através de um eixo bidirecional, cujo equilíbrio depende da composição da comunidade microbiana que habita o intestino. O papel modulador que este ecossistema exerce sobre o eixo cérebro-intestino será também abordado.All animals, including humans, have developed associations with microbial communities. These collections of microorganisms, collectively referred to as microbiota, inhabit environmentally exposed body surfaces, with the community of the gastrointestinal tract representing the highest density collection of microorganisms in the human body. The human body establishes a dynamic relationship with the enteric microbiota, and this interaction is essential for homeostasis, because states of dysbiosis favor the onset of gastrointestinal diseases. Among these is the Irritable Bowel Syndrome, a functional disease of the gastrointestinal system characterized by pain, abdominal distension and changes in motility, which has been associated with a high prevalence of psychiatric disorders. In this work, our main goal is to conduct a literature review, using the Pubmed search engine, with the objective of characterizing the functions of the gut microbiota, understanding the influence of the gut microbiota on the etiology of Irritable Bowel Syndrome, and addressing the interrelationship between Irritable Bowel Syndrome and psychiatric disease. With this work, we reveal the existence of interactions between hosts and their resident bacterial communities in the formation and function of neurological systems. These relationships, which involve intricate chemical and immunological signaling pathways, play a role in health and how we understand neurological disease. Once perceived as defects in brain processes, mental illness today is far removed from the exclusively brain-centric perspective. In fact, the brain and gut communicate, through a bidirectional axis, whose balance depends on the composition of the microbial community inhabiting the gut. The modulating role that this ecosystem plays on the brain-intestine axis will also be addressed

Structural and nucleic acid binding properties of hepatitis delta virus small antigen

AIM: To further characterize the structure and nucleic acid binding properties of the 195 amino acid small delta antigen, S-HDAg, a study was made of a truncated form of S-HDAg, comprising amino acids 61-195 (∆60HDAg), thus lacking the domain considered necessary for dimerization and higher order multimerization. METHODS: Circular dichroism, and nuclear magnetic resonance experiments were used to assess the structure of ∆60HDAg. Nucleic acid binding properties were investigated by gel retardation assays. RESULTS: Results showed that the truncated ∆60HDAg protein is intrinsically disordered but compact, whereas the RNA binding domain, comprising residues 94-146, adopts a dynamic helical conformation. We also found that ∆60HDAg fails to multimerize but still contains nucleic acid binding activity, indicating that multimerization is not essential for nucleic acid binding. Moreover, in agreement with what has been previously reported for full-length protein, no apparent specificity was found for the truncated protein regarding nucleic acid binding. CONCLUSION: Taken together these results allowed concluding that ∆60HDAg is intrinsically disordered but compact; ∆60HDAg is not a multimer but is still capable of nucleic acid binding albeit without apparent specificity.publishersversionpublishersversionpublishe

Hsp70 Chaperones and Type I PRMTs Are Sequestered at Intranuclear Inclusions Caused by Polyalanine Expansions in PABPN1

Genomic instability at loci with tandem arrays of simple repeats is the cause for many neurological, neurodegenerative and neuromuscular diseases. When located in coding regions, disease-associated expansions of trinucleotide repeats are translated into homopolymeric amino acid stretches of glutamine or alanine. Polyalanine expansions in the poly(A)-binding protein nuclear 1 (PABPN1) gene causes oculopharyngeal muscular dystrophy (OPMD). To gain novel insight into the molecular pathophysiology of OPMD, we studied the interaction of cellular proteins with normal and expanded PABPN1. Pull-down assays show that heat shock proteins including Hsp70, and type I arginine methyl transferases (PRMT1 and PRMT3) associate preferentially with expanded PABPN1. Immunofluorescence microscopy further reveals accumulation of these proteins at intranuclear inclusions in muscle from OPMD patients. Recombinant PABPN1 with expanded polyalanine stretches binds Hsp70 with higher affinity, and data from molecular simulations suggest that expansions of the PABPN1 polyalanine tract result in transition from a disordered, flexible conformation to a stable helical secondary structure. Taken together, our results suggest that the pathological mutation in the PABPN1 gene alters the protein conformation and induces a preferential interaction with type I PRMTs and Hsp70 chaperones. This in turn causes sequestration in intranuclear inclusions, possibly leading to a progressive cellular defect in arginine methylation and chaperone activity

Clastosome: a subtype of nuclear body enriched in 19S and 20S proteasomes, ubiquitin, and protein substrates of proteasome.

Nuclear bodies represent a heterogeneous class of nuclear structures. Herein, we describe that a subset of nuclear bodies is highly enriched in components of the ubiquitin-proteasome pathway of proteolysis. We coined the term clastosome (from the Greek klastos, broken and soma, body) to refer to this type of nuclear body. Clastosomes contain a high concentration of 1) ubiquitin conjugates, 2) the proteolytically active 20S core and the 19S regulatory complexes of the 26S proteasome, and 3) protein substrates of the proteasome. Although detected in a variety of cell types, clastosomes are scarce under normal conditions; however, they become more abundant when proteasomal activity is stimulated. In contrast, clastosomes disappear when cells are treated with proteasome inhibitors. Protein substrates of the proteasome that are found concentrated in clastosomes include the short-lived transcription factors c-Fos and c-Jun, adenovirus E1A proteins, and the PML protein. We propose that clastosomes are sites where proteolysis of a variety of protein substrates is taking place

The intranuclear mobility of messenger RNA binding proteins is ATP dependent and temperature sensitive

fAter being released from transcription sites, messenger ribonucleoprotein particles (mRNPs) must reach the nuclear pore complexes in order to be translocated to the cytoplasm. Whether the intranuclear movement of mRNPs results largely from Brownian motion or involves molecular motors remains unknown. Here we have used quantitative photobleaching techniques to monitor the intranuclear mobility of protein components of mRNPs tagged with GFP. The results show that the diffusion coefficients of the poly(A)-binding protein II (PABP2) and the export factor TAP are significantly reduced when these proteins are bound to mRNP complexes, as compared with nonbound proteins. The data further show that the mobility of wild-type PABP2 and TAP, but not of a point mutant variant of PABP2 that fails to bind to RNA, is significantly reduced when cells are ATP depleted or incubated at 22°C. Energy depletion has only minor effects on the intranuclear mobility of a 2,000-kD dextran (which corresponds approximately in size to 40S mRNP particles), suggesting that the reduced mobility of PABP2 and TAP is not caused by a general alteration of the nuclear environment. Taken together, the data suggest that the mobility of mRNPs in the living cell nucleus involves a combination of passive diffusion and ATP-dependent processes

In vivo aggregation properties of the nuclear poly(A)-binding protein PABPN1

A broad range of degenerative diseases is associated with intracellular inclusions formed by toxic, aggregation-prone mutant proteins. Intranuclear inclusions constitute a pathological hallmark of oculopharyngeal muscular dystrophy (OPMD), a dominantly inherited disease caused by (GCG) repeat expansions in the gene that encodes for nuclear poly(A) binding protein (PABPN1). The mutation results in an extended polyalanine stretch that has been proposed to induce protein aggregation and formation of intranuclear inclusions. Here we show that normal PABPN1 is inherently aggregation-prone when exogenously expressed in either HeLa or myogenic C2 cells. Similar deposits of insoluble PABPN1 are formed by variant forms of the protein containing either a polyalanine expansion or a complete deletion of the polyalanine tract, indicating that the mutation responsible for OPMD is not essential for formation of PABPN1 inclusions. In contrast, interfering with any of the protein domains required for stimulation of poly(A) polymerase prevents the formation of inclusions. Most surprisingly, photobleaching experiments reveal that both normal and expanded PABPN1 molecules are not irreversibly sequestered into aggregates, but rather move rapidly in and out of the inclusions. These findings have important implications for the interpretation of OPMD model systems based on exogenous expression of PABPN1