Diet-Derived Short Chain Fatty Acids Stimulate Intestinal Epithelial Cells To Induce Mucosal Tolerogenic Dendritic Cells.

The gastrointestinal tract is continuously exposed to many environmental factors that influence intestinal epithelial cells and the underlying mucosal immune system. In this article, we demonstrate that dietary fiber and short chain fatty acids (SCFAs) induced the expression of the vitamin A-converting enzyme RALDH1 in intestinal epithelial cells in vivo and in vitro, respectively. Furthermore, our data showed that the expression levels of RALDH1 in small intestinal epithelial cells correlated with the activity of vitamin A-converting enzymes in mesenteric lymph node dendritic cells, along with increased numbers of intestinal regulatory T cells and a higher production of luminal IgA. Moreover, we show that the consumption of dietary fiber can alter the composition of SCFA-producing microbiota and SCFA production in the small intestines. In conclusion, our data illustrate that dietary adjustments affect small intestinal epithelial cells and can be used to modulate the mucosal immune system.

Vagal innervation is required for the formation of tertiary lymphoid tissue in colitis.

Tertiary lymphoid tissue (TLT) is lymphoid tissue that forms in adult life as a result of chronic inflammation in a tissue or organ. TLT has been shown to form in a variety of chronic inflammatory diseases, though it is not clear if and how TLT develops in the inflamed colon during inflammatory bowel disease. Here, we show that TLT develops as newly formed lymphoid tissue in the colon following dextran sulphate sodium induced colitis in C57BL/6 mice, where it can be distinguished from the preexisting colonic patches and solitary intestinal lymphoid tissue. TLT in the inflamed colon develops following the expression of lymphoid tissue-inducing chemokines and adhesion molecules, such as CXCL13 and VCAM-1, respectively, which are produced by stromal organizer cells. Surprisingly, this process of TLT formation was independent of the lymphotoxin signaling pathway, but rather under neuronal control, as we demonstrate that selective surgical ablation of vagus nerve innervation inhibits CXCL13 expression and abrogates TLT formation without affecting colitis. Sympathetic neuron denervation does not affect TLT formation. Hence, we reveal that inflammation in the colon induces the formation of TLT, which is controlled by innervation through the vagus nerve.

Vitamin A metabolism and mucosal immune function are distinct between BALB/c and C57BL/6 mice.

The vitamin A metabolite retinoic acid (RA) has been reported to suppress Th1 responses and enhance Th2 responses. Here, we investigated whether differences in vitamin A metabolism could underlie the differences between C57BL/6 and BALB/c mice, which are reportedly seen as Th1 and Th2 responders, respectively. BALB/c mice were shown to have higher intestinal epithelial expression of RALDH1 (where RALDH is retinaldehyde dehydrogenase), and, consequently, higher RALDH activity in MLN-DCs, leading to an increased ability to induce IgA class switching in B cells. Furthermore, within BALB/c mice, induction of IgA secretion as well as increased accumulation of regulatory T cells (Treg) in the intestinal lamina propria was observed. Additionally, as BALB/c mice are more resistant to dextran sulphate sodium (DSS) induced colitis, mice that lacked vitamin A in their diet had a more severe form of DSS-induced colitis compared to control mice. Therefore, the level of RA production and consequently the degree of RA-mediated signaling is crucial for the efficiency of the mucosal immune system.

Expression of retinaldehyde dehydrogenase enzymes in mucosal dendritic cells and gut-draining lymph node stromal cells is controlled by dietary vitamin A.

The vitamin A metabolite retinoic acid (RA) plays a crucial role in mucosal immune responses. We demonstrate in this study that RA-producing retinaldehyde dehydrogenase (RALDH) enzymes are postnatally induced in mesenteric lymph node (MLN) dendritic cells (DCs) and MLN stromal cells. RALDH enzyme activity in lamina propria-derived CD103(+) MLN-DCs did not depend on TLR signaling. Remarkably, RA itself could directly induce RALDH2 in both DCs and stromal cells in vitro. Furthermore, upon provision of a vitamin A-deficient diet, it was found that RA-mediated signaling was strongly reduced within the small intestines, while RALDH2 mRNA and RALDH enzyme activity in lamina propria DCs and MLN-DCs, as well as RALDH2 mRNA expression in MLN stromal cells, were strongly diminished. Moreover, supply of vitamin A to vitamin A-deficient mice restored RA-mediated signaling in the intestine and RALDH activity in lamina propria-derived CD103(+) MLN-DCs. Our results show that RA-dependent signaling within the intestine is indispensable for RALDH activity in the draining MLN.

Stem cells from adipose tissue allow challenging new concepts for regenerative medicine.

The perspective of an innovative new concept integrating tissue-engineering techniques with an established surgical technique is described. The focus is primarily on a one-step surgical procedure using adipose tissue-derived mesenchymal stem cells, a calcium phosphate scaffold as a carrier, and a bioresorbable polymer cage to facilitate spinal interbody fusion. We address the harvesting and processing of clinically relevant quantities of adipose tissue-derived mesenchymal stem cells, triggering of these stem cells toward lineage-specific differentiation, seeding of the triggered stem cells on a bioresorbable scaffold, and implantation of the resulting tissue-engineered construct. The integrated steps can be accomplished within one surgical procedure in a surgical theater. Although the proposed concept has been developed for spinal fusion, potential application in other surgical disciplines is presumed realistic.

Adipose tissue-derived mesenchymal stem cells acquire bone cell-like responsiveness to fluid shear stress on osteogenic stimulation.

To engineer bone tissue, mechanosensitive cells are needed that are able to perform bone cell-specific functions, such as (re)modeling of bone tissue. In vivo, local bone mass and architecture are affected by mechanical loading, which is thought to provoke a cellular response via loading-induced flow of interstitial fluid. Adipose tissue is an easily accessible source of mesenchymal stem cells for bone tissue engineering, and is available in abundant amounts compared with bone marrow. We studied whether adipose tissue-derived mesenchymal stem cells (AT-MSCs) are responsive to mechanical loading by pulsating fluid flow (PFF) on osteogenic stimulation in vitro. We found that ATMSCs show a bone cell-like response to fluid shear stress as a result of PFF after the stimulation of osteogenic differentiation by 1,25-dihydroxyvitamin D3. PFF increased nitric oxide production, as well as upregulated cyclooxygenase-2, but not cyclooxygenase-1, gene expression in osteogenically stimulated AT-MSCs. These data suggest that AT-MSCs acquire bone cell-like responsiveness to pulsating fluid shear stress on 1,25-dihydroxyvitamin D3-induced osteogenic differentiation. ATMSCs might be able to perform bone cell-specific functions during bone (re)modeling in vivo and, therefore, provide a promising new tool for bone tissue engineering.

Osteogenic differentiation strategies for adipose-derived mesenchymal stem cells.

Adipose stem cell preparations, either obtained as a freshly isolated so-called stromal vascular fraction (SVF) or as cells cultured to homogeneity and then referred to as adipose stem cells (ASCs), have found widespread use in a broad variety of studies on tissue engineering and regenerative medicine applications, including bone repair.For newcomers within the field, but also for established research laboratories having up to 10 years of expertise in this research area, it may be convenient to strive for, and use consensus protocols (1) for studying the osteogenic differentiation potential of ASC preparations in vitro, and (2) for osteogenic induction regimes for in vivo implementation. To assist in achieving this goal, this chapter describes various step-by-step osteogenic differentiation protocols for adipose-derived stem cell populations (SVF as well as ASCs) currently applied within our laboratory, with particular emphasis on protocols aimed at intra-operative use. The protocols describe the use of inducing compounds, including the bone morphogenetic proteins (BMPs), 1,25-dihydroxyvitamin-D3, and polyamines, as well as methods and parameters for evaluating the level of differentiation achieved.We would appreciate receiving feedback on the protocols described; this will facilitate the development of consensus protocols, which in turn will allow better comparison of data sets generated by different research groups. This continuing standardization, which might be reported on at international meetings like those of IFATS ( http://www.IFATS.org ), might be of benefit for the whole ASC research community.

Differential effects of bone morphogenetic protein-2 and transforming growth factor-beta1 on gene expression of collagen-modifying enzymes in human adipose tissue-derived mesenchymal stem cells.

Adipose tissue-derived mesenchymal stem cells (AT-MSCs) in combination with bone morphogenetic protein-2 (BMP-2) or transforming growth factor-beta1 (TGF-beta1) are under evaluation for bone tissue engineering. Posttranslational modification of type I collagen is essential for functional bone tissue with adequate physical and mechanical properties. We investigated whether BMP-2 (10-100 ng/mL) and/or TGF-beta1 (1-10 ng/mL) affect gene expression of alpha2(I) procollagen and collagen-modifying enzymes, that is, lysyl oxidase and lysyl hydroxylases 1, 2, and 3 (encoded by PLOD1, 2, and 3), by human AT-MSCs. BMP-2, but not TGF-beta1, increased alkaline phosphatase activity after 28 days, indicating osteogenic differentiation of AT-MSCs. At day 4, both BMP-2 and TGF-beta1 upregulated alpha2(I) procollagen and PLOD1, which was downregulated at day 28. TGF-beta1, but not BMP-2, downregulated PLOD3 at day 28. Lysyl oxidase was upregulated by TGF-beta1 at day 4 and by BMP-2 at day 7. Neither BMP-2 nor TGF-beta1 affected PLOD2. In conclusion, these results suggest that AT-MSCs differentially respond to BMP-2 and TGF-beta1 with changes in gene expression of collagen-modifying enzymes. AT-MSCs may thus be able to appropriately modify type I collagen to form a functional bone extracellular matrix for tissue engineering, dependent on the growth factor added.