Figure 1.
Eating probiotics blocks a gut microbiota-immunity-obesity axis.
L. reuteri protects mice from Western diet-associated obesity. Data are shown in male outbred Swiss mice at the age of 5 months. Numerous crown-like structures (CLS) caused by adipocyte death-related inflammation, and focal pyogranulomatous inflammation (PGI) arise in abdominal fat of ‘fast food’-fed but not probiotic-fed animals. Probiotics increase anti-inflammatory Foxp3+ regulatory (Treg) cells and reduce pro-inflammatory Il17 protein to restore immune balance coinciding with a slender physique (a and b), without restructuring GI microbial communities (c). In the same mice, serum cytokine analysis shows that the pro-inflammatory Il-17-associated effect of obesity is systemic, and that L. reuteri negates this effect up-regulating the anti-inflammatory cytokine Il-10 (d). Humans frequently eating ‘fast food’ also show an elevated ratio of pro-inflammatory IL17+/anti-inflammatory Foxp3+ Treg in peripheral blood cells compared to subjects never eating ‘fast food’ (e). Probiotic-consuming slim mice chose similar calories when compared with obese animals, regardless of baseline diet, highlighting potential for translational medicine (f). Fat histology: Hematoxylin and eosin, Bars = 50 µm; MLN Immunohistochemistry: Diaminobenzidine chromogen, hematoxylin counterstain, Bars = 8.3 µm.
Figure 2.
Dietary supplementation with L. reuteri protects from age-associated Western diet obesity.
Specifically, the abdominal (epididymal) fat mass is significantly reduced in probiotic-consuming Swiss mice (a). The slenderizing effect of L. reuteri is also observed in the subcutaneous fat depot. The subcutaneous fat layer (SF) is significantly thicker and has many CLS (inset) in “fast food”-fed mice in contrast to mice eating the same diet and L. reuteri. There is thicker dermis and increased subcutaneous hair follicle profiles in the left inset of the “fast food”+probiotic skin image (b). Fad pad weight and subcutaneous fat thickness histomorphometric analyses show that probiotics protect from age-associated obesity irrespective of baseline diet (c). Eating probiotics benefits aged Swiss mice as well as the young animals, evident here from the body weight analysis of 7- and 9-months-old male and female mice (d). Skin histology: Hematoxylin and eosin, Bars = 250 µm.
Figure 3.
Mice exhibit an Interleukin 10-dependent Treg cell-mediated gut microbiota-immunity-obesity axis.
Genetically-inbred C57BL/6 strain mice similarly benefit from probiotic protection against Western diet-associated obesity and fat pathology, including CLS and focal pyogranulomatous inflammation as shown here in males at 5 months of age (a). Interleukin (Il) 10-deficient C57BL/6 male mice eating Westernized chow failed to benefit from oral L. reuteri supplementation. Mice from both experimental groups were obese and had increased CLS that were often seen coalescing to form focally diffuse areas of adipocyte necrosis (b). Fat histology: Hematoxylin and eosin. Bars = 250 µm (a) and 100 µm (b).
Figure 4.
Diet-associated fat pathology is transferable to naïve animals using purified T-lymphocytes.
Adoptive transfer of purified CD4+ cells from C57BL/6 wild type donor mice eating probiotics into C57BL/6 Rag2-null mice was sufficient to significantly reduce recipient body fat depots such as subcutaneous fat, as well as ameliorate abdominal fat pathology (a). Control diet-fed mice used as donors for lymphocyte transfer experiments showed IL10-dependent L.reuteri benefits including significantly less CLS in their abdominal fat (b). This immune-mediated protection requires Il10, as adoptive transfer of CD4+ cells from probiotic-fed Il10-deficient donors did not protect the recipient mice from obesity and associated fat pathology (c). Purified wild type CD4+ FoxP3+ Treg cells from mice eating L. reuteri were sufficient for beneficial effects in Rag2-null recipient mice rescuing them from obesity-associated pathology (d). Skin and fat histology: Hematoxylin and eosin. Bars skin = 250 µm, edididymal fat = 50 µm.
Figure 5.
Anti-obesity protection of oral probiotics in outbred Swiss mice requires CD25+ immune cells.
Depletion of CD4+CD25+ Treg cells entirely inhibits probiotic-induced protection from age-associated obesity and abdominal fat pathology (a). Probiotics protect from weight gain unless mice were simultaneously treated with anti-CD25 antibody, in which case animals rapidly became obese. Frequency of prototype crown-like structures was increased in abdominal fat after depletion of CD25+ cells but not in sham IgG-treated control animals (b). Fat histology: Hematoxylin and eosin. Bars = 100 µm.
Figure 6.
Proposed mechanistic overview.
In order to explain the ‘fast food’ versus ‘yogurt’ age-associated weight disparity observed in human subjects, we propose that Western-style dietary habits alter gut microbiota fueling an IL-6 driven, IL-17-dominant, systemic smoldering inflammatory milieu, ultimately leading to a vicious circle of obesity and inflammation. On the other hand, individuals consuming probiotic yogurt enrich their gut with probiotic bacteria that stimulate the anti-inflammatory arm of the immune system. Potent IL-10-associated Treg responses in these individuals rescue them from the inflammation-obesity cycle, thus increasing likelihood of a leaner physique.