Retinoic Acid Is Elevated in the Mucosa of Patients With Active Ulcerative Colitis and Displays a Proinflammatory Role by Augmenting IL-17 and IFNγ Production.

BACKGROUND: All-trans retinoic acid (RA) plays a crucial role in promoting Foxp3+ Treg generation while reciprocally inhibiting Th1/Th17 generation. Our previous research highlighted that in the face of inflammatory conditions, RA plays a contrary role where it aggravates intestinal inflammation by promoting interferon (IFN) γ and interleukin (IL)-17 differentiation in vitro. METHODS: In this study we translated our in vitro results into a clinical setting where we estimated mucosal and serum RA levels along with the immunophenotypic profile (IL-17, IFNγ, Foxp3, IL-10) in adaptive (CD4, CD8) and innate-like T cells (mucosal associated invariant T cells and γδ T cells) in patients with ulcerative colitis in remission or with active inflammation. RESULTS: This is the first study to estimate RA levels in the human gut and shows that patients with active disease had increased mucosal RA levels as compared with patients in remission (4.0 vs 2.5 ng/mL; P < 0.01) and control patients (3.4 vs 0.8 ng/mL; P < 0.0001). This effect was accompanied by significantly elevated IL-17 and IFNγ in tissue CD4+, CD8+, mucosal associated invariant T+ cells, and γδ + T cells. Moreover, the raised RA levels in patients with active disease showed a positive correlation with proinflammatory cytokines (IL-17, IFNγ) and a negative correlation with IL-10. We also found that RA negatively correlated with IL-9, thereby reinstating our previous finding that RA inhibits Th9 differentiation. CONCLUSIONS: These data confirm our previous in vitro results that in the presence of inflammation, RA plays a crucial role in maintaining gut inflammation by upregulating proinflammatory markers.

Peripheral blood-derived monocytes show neuronal properties and integration in immune-deficient rd1 mouse model upon phenotypic differentiation and induction with retinal growth factors.

BACKGROUND: Cell therapy is one of the most promising therapeutic interventions for retinitis pigmentosa. In the current study, we aimed to assess if peripheral blood-derived monocytes which are highly abundant and accessible could be utilized as a potential candidate for phenotypic differentiation into neuron-like cells. METHODS: The peripheral blood-derived monocytes were reconditioned phenotypically using extrinsic growth factors to induce pluripotency and proliferation. The reconditioned monocytes (RM) were further incubated with a cocktail of growth factors involved in retinal development and growth to induce retinal neuron-like properties. These cells, termed as retinal neuron-like cells (RNLCs) were characterized for their morphological, molecular and functional behaviour in vitro and in vivo. RESULTS: The monocytes de-differentiated in vitro and acquired pluripotency with the expression of prominent stem cell markers. Treatment of RM with retinal growth factors led to an upregulation of neuronal and retinal lineage markers and downregulation of myeloid markers. These cells show morphological alterations resembling retinal neuron-like cells and expressed photoreceptor (PR) markers. The induced RNLCs also exhibited relative membrane potential change upon light exposure suggesting that they have gained some neuronal characteristics. Further studies showed that RNLCs could also integrate in an immune-deficient retinitis pigmentosa mouse model NOD.SCID-rd1 upon sub-retinal transplantation. The RNLCs engrafted in the inner nuclear layer (INL) and ganglion cell layer (GCL) of the RP afflicted retina. Mice transplanted with RNLCs showed improvement in depth perception, exploratory behaviour and the optokinetic response. CONCLUSIONS: This proof-of-concept study demonstrates that reconditioned monocytes can be induced to acquire retinal neuron-like properties through differentiation using a defined growth media and can be a potential candidate for cell therapy-based interventions and disease modelling for ocular diseases.