Retinoic acid (RA) is commonly used in vitro to differentiate stem cell populations including adult neural stem cells into neurons; however, the in vivo function of RA during adult neurogenesis remains largely unexplored. We found that depletion of RA in adult mice leads to significantly decreased neuronal differentiation within the granular cell layer of the dentate gyrus. RA contribution to neurogenesis occurs early, for RA deficiency also results in a decrease in newborn cells expressing an immature neuronal marker. Furthermore, although proliferation is unaffected during RA absence, cell survival is significantly reduced. Finally, a screen for retinoid-induced genes identifies metabolic targets including the lipid transporters, CD-36 and ABCA-1, the lipogenic master regulator SREBP1c as well as components of the Wnt signaling pathway. Our results reveal RA as a crucial contributor to early stages of adult neurogenesis and survival in vivo.hippocampus ͉ neural stem cells ͉ retinoic acid receptor ͉ vitamin A

Antibody responses to T cell-dependent antigens are reduced during vitamin A (VA) deficiency and restored by retinoids. To test whether retinoic acid (RA) and polyinosinic:polycytidylic acid (PIC), an inducer of interferons, can increase specific antibody production, VA-deficient rats were treated with all-trans-RA, PIC, or both at the time of primary immunization with tetanus toxoid. VA-deficient rats produced low primary and secondary anti-tetanus IgG responses (P<.001 vs. VA-sufficient controls). Both responses were increased synergistically by RA plus PIC (P<.0001). In VA-deficient spleens, mRNAs were low for interleukin (IL)-2 receptor-beta, interferon regulatory factor-1, and signal transducer and activator of transcription 1. Each, however, was induced by RA plus PIC (P<.0001 vs. controls). Conversely, IL-12 and IL-10 mRNAs were elevated in VA deficiency and were induced by PIC and suppressed by RA. Thus, RA plus PIC appears to be a promising combination for stimulating antigen-specific immunity. Several molecular factors identified here may partially account for the observed enhancement.

Summary Retinoic acid (RA), an active metabolite of vitamin A, may synergize with interferons (IFN) to evoke a heightened immune response, suggesting combination therapy as a promising treatment for various cancers. Recently, we demonstrated a strong synergism between RA and polyriboinosinic : polyribocytidylic acid (PIC), an inducer of IFN, on antibody production in immunocompromised vitamin A‐deficient animals. In the present study, we examined whether this combination could potentiate T‐cell‐dependent antibody production in non‐immunocompromised rats. Forty male Lewis rats were treated with 100 µg all‐trans‐RA, 20 µg PIC, or the combination in either an 11‐d study to evaluate antibody production, changes in lymphocyte populations, and cell proliferation, or a 21‐hr study to evaluate early changes in lymphocyte populations and gene expression. The combination of RA + PIC significantly potentiated anti‐tetanus IgG levels (P < 0·002). Similarly, this combination also increased the numbers of B cells and major histocompatibility complex (MHC) class II+ cells in spleen and lymph nodes, and natural killer (NK) cells in spleen and blood (P < 0·05). RA + PIC‐treated rats had significantly higher levels of interleukin (IL)‐10, IL‐12, and signal transducer and activator of transcription‐1 (STAT‐1) mRNA (P < 0·05), and STAT‐1 protein (P < 0·02). Treatments administered in vivo significantly modulated T‐cell proliferation to anti‐CD3/phorbol myristyl acetate + IFN‐αex vivo. These changes in antibody production, cell distribution, cytokine gene expression, and T‐cell proliferation suggest that the combination of RA + PIC stimulates humoral and cell‐mediated immunity, and deserves further testing in models of cancer chemoprevention in vivo.

Natural killer (NK) cells function in the regulation of immune responses and in the surveillance of malignant or other abnormal cells. Little is known of the effects of chronic marginal vitamin A (VA) status or VA supplementation, or their interaction with age, on NK cell number and cytolytic activity. We have conducted a two-factor (diet, age) study in which male Lewis rats were fed AIN-93M diet, modified to contain either 0.3 (designated marginal), 4.0 (control) or 50 (supplemented) mg retinol equivalents (RE)/kg diet, from the time of weaning until the ages of 2.5 mo (young), 8-10 mo (middle-aged) or 18-20 mo (old). Natural killer cells were identified and quantified in peripheral blood mononuclear cells (PBMC) and spleen with the use of flow cytometry, and NK cell cytotoxicity was assayed. The number and percentage of PBMC NK cells increased with age (P < 0.0001 by two-way ANOVA). For all age groups, values were lowest in rats with marginal VA status (P < 0.0001 vs. controls). NK cell lytic activity also declined with age (P = 0. 0003). As a result, NK cell lytic efficiency (lytic activity per NK cell) decreased markedly with age (P < 0.0001). Regardless of the donor's age or VA status, PBMC NK cell cytotoxicity doubled (100 +/- 25% increase) after exposure to interferon-alpha (5 x 10(5) U/L for 1 h before assay), indicating that IFN-stimulated lytic activity was related directly to basal NK cell activity. If the relationships observed in this animal model can be applied to humans, these data suggest that elderly people consuming diets chronically low in VA may be at increased risk for infectious or neoplastic diseases.

Lung cancer is the leading cause of cancer-related death in developed countries. Non-small cell lung cancer (NSCLC) represents 80% of the total lung cancer cases and is comprised of adenocarcinoma, adenosquamous carcinoma, squamous cell carcinoma and large cell carcinoma (LCC) subtypes. The ability of LCC to metastasize earlier than the other forms of lung cancer suggests anti-angiogenic drugs as effective agents to combat this cancer. Thalidomide is an anti-angiogenic drug that has shown promise in multiple hematological diseases, and myeloma and other cancers. However, the molecular mechanism by which thalidomide exerts its effects is poorly understood. Therefore, we evaluated the effectiveness of thalidomide on NSCLC cell growth, and found that LCC cells were growth inhibited by 40-60%. This effect seemed specific to LCC cancer cells, since other forms of NSCLC were only mildly affected by thalidomide. At the molecular level, thalidomide increased peroxisome proliferator-activated receptor gamma (PPARgamma) protein dose-dependently, and peroxisome proliferator response element activity. Further, thalidomide treatment of LCC cells decreased nuclear factor kappa B activity in a dose-dependent fashion, increased apoptosis and decreased the expression of angiogenic proteins. In our mouse xenograft model of lung cancer, we found that intratumoral thalidomide caused a 64% decrease in tumor growth; moreover, tumors from the thalidomide-treated mice expressed higher PPARgamma, than tumors from control mice. This study shows the antitumor activity of thalidomide against LCC tumors and suggests a model in which thalidomide exerts its antitumor effects on LCC cells through the induction of PPARgamma and subsequent downstream signaling. To our knowledge, this is the first study to show a link between thalidomide and PPARgamma.