En un estudio reciente publicado en Huésped celular y microbiolos investigadores estudiaron las interacciones entre la dieta y los microbios comensales en la autoinmunidad.
La microbiota comensal y la dieta pueden influir en los mecanismos de autoinmunidad en trastornos como la diabetes tipo 1 (DT1). Sin embargo, no está claro si los microbios median en las intervenciones dietéticas y justifica una mayor investigación. La identificación de intervenciones dietéticas independientes del microbioma y la exploración de interacciones particulares de la dieta comensal que potencien la autoinmunidad podrían ayudar a mejorar el manejo de los trastornos autoinmunes.
Sobre el estudio
En el presente estudio, los investigadores exploraron los efectos regulados y no regulados por el microbioma de las intervenciones dietéticas en el manejo de los trastornos autoinmunes.
Se seleccionaron ratones no obesos diabéticos (NOD). transglutaminasa 2 (TGM2) knockout (KO) para los experimentos, y se analizó la caseína hidrolizada (HC) como fuente de proteína. Para investigar si los efectos antidiabéticos de la dieta a base de caseína dependían del microbioma, se expuso a ratones NOD, en condiciones libres de gérmenes (GF) y libres de patógenos específicos (SPF), a formulaciones que contenían proteína de caseína intacta (IC ), o para comer (intervención dietética de control).
Para dilucidar los mecanismos involucrados en la protección contra la diabetes tipo 1, se evaluaron los efectos de la caseína en los linfocitos T autoinmunes, para lo cual se transfirieron células de bazo de animales murinos no diabéticos con dieta de caseína o dieta chow a NOD.TCRaKO o NOD inmunosuprimidos. scid o ratones. Posteriormente, se determinó el número de linfocitos T reguladores (Tregs) en las células de los islotes pancreáticos infiltrados y en los ganglios linfáticos pancreáticos (PLN) de los animales murinos.
Para investigar si la caseína influye en la secreción/producción de insulina, dando como resultado una atenuación indirecta de la autoinmunidad, se llevaron a cabo la prueba de tolerancia a la insulina intraperitoneal (IPITT) y la prueba de tolerancia a la glucosa intraperitoneal (IPGTT). Se detectaron microbios bacterianos que digieren gluten, se prepararon digestos de gluten y los digestos de gluten estimularon macrófagos peritoneales para investigar la contribución de la proteólisis del gluten a la inmunidad inmunológica innata.
Los sobrenadantes de cultivo se probaron para respuestas a corto plazo [tumor necrosis factor (TNF) expression] y respuestas tardías [interleukin-6 (IL-6) expression. The digests were treated with polymyxin B, and Limulus amebocyte lysate (LAL) assays were performed. Pancreatic islets of NOD.scid murine animals were subjected to single-cell ribonucleic acid (RNA) sequencing (SCS), T cell receptor (TCR) sequencing, and 16S ribosomal ribonucleic acid (rRNA) sequencing analyses, and the bacterial ribosomal RNA was amplified using polymerase chain reaction (PCR).
In addition, differential gene expression, multiparameter flow cytometry, enzyme-linked immunospot (ELISPOT), Western blot, and immunofluorescence analyses were performed. T lymphocyte proliferation was assessed in vitro and in vivo. CRISPR-Cas9 analysis was performed to investigate whether transglutaminase 2 gene activation promoted T1D. Further, the team investigated whether gnotobiotic mice colonization with E. faecalis would facilitate T1D development, and the role of lipopolysaccharide-driven signaling in T1D development was explored.
Results
The casein-based diet protected non-obese diabetic murine animals in traditional and GF conditions by physiologic improvements in insulin secretion to suppress the activation of autoimmune mechanisms independent of the microbiome composition. Gluten-activated autoimmune pathways, triggered by microbe-mediated gluten proteolysis. Cytokine expression was stimulated by lipopolysaccharide-dependent proteolytic gluten digestion.
Type 1 diabetes developed among germ-free animals colonized with E. faecalis containing gluten-digesting protease enzymes but not among animals colonized with bacteria lacking proteases. E. faecalis-mediated digestion of gluten-induced T lymphocyte-activating peptide molecules and enhanced innate immunological mechanisms by increasing the reactivity of macrophages to lipopolysaccharides. Gnotobiotic non-obese diabetic Toll4– murine animals colonized with Enterococcus faecalis on casein+ gluten diets showed resistance to type 1 diabetes.
The HC diet lowered β lymphocyte stress and T1D in a microbiome-independent manner. The promotion of gluten-mediated pancreatic islet cell inflammation depended on the gluten digestion ability of the commensal microbes. The findings indicated that altering the physiologic pathways of the target organ (such as the pancreas for insulin production) might inhibit or delay autoimmune activation, which is attainable irrespective of the commensal microbiome complexity.
Two critical biological functions of gut microbes associated with proteolytic gluten digestion were noted, i.e., the secretion of adaptive immune system-activating peptides, and enhancement of the LPS-regulated induction of innate immunological mechanisms. The digestion of gluten by microbial protease enzymes promoted type 1 diabetes development.
HC-regulated protection was not related to the active inhibition of immune effector pathways, but instead due to a decrease in the initial sensitization steps. The decrease in insulin production by casein did not depend on the adaptive immunological system-mediated injury, indicative of a direct impact on hormone-producing cells. Gluten potentiated autoimmunity by directly acting on the immunological system, and promoted diabetogenic pathways.
Overall, the study findings showed that casein-based diets could probably lower the incidence of autoimmune or type 1 diabetes by improving the insulin-secretion physiology, irrespective of the commensal microbiome composition. Protease-producing microbial organisms and gluten could reverse HC-regulated protection.
