Glucocorticoids suppressed osteoblast differentiation by decreasing Sema3A expression via the PIK3/Akt pathway.

Glucocorticoids(GCs) are extensively used to treat inflammatory and autoimmune diseases. Excessive prolonged exposure to glucocorticoids is associated with an increased risk of osteoporosis. The inhibition of osteoblast differentiation by GCs is suggested as a major cause for GCs-induced osteoporosis (GIO). However, the precise mechanism underlying the role of GCs in osteoblasts differentiation is not fully elucidated. Semaphorin 3A (Sema3A), a secreted member of the Semaphorin family, enhances bone formation and promotes fracture healing, which is known to increase osteoblastic differentiation and stimulate osteogenesis in bone metabolism. Here, the present study explored the effect of Sema3A in osteoblast differentiation using dexamethasone (Dex) treatment of bone marrow stromal cells (BMSCs). Dex treatment decreased Sema3A expression in BMSCs in a dose-dependent manner. Moreover, Dex stimulation suppressed the differentiation of osteoblasts by reducing alkaline phosphatase (ALP) activity, osteoblastic marker genes expression and mineralization, but all of these effects were ameliorated by exogenous recombinant Sema3A administration. Furthermore, exogenous Sema3A administration reversed the Dex-mediated decrease in nuclear accumulation of ß-catenin and ß-catenin activity in BMSCs. Meanwhile, Dex was capable of simultaneously suppressing the phosphorylation of protein kinase B(Akt) and the expression level of Sema3A in BMSCs. These changes were significantly abolished by the PI3K/Akt agonist. These results suggest that Dex inhibits osteoblast differentiation by suppressing Sema3A expression via the PI3K/Akt pathway. These data provide new insights into the molecular mechanisms of Dex-induced osteoblast differentiation inhibition.

Modulation of semaphorin 3A expression by calcium concentration and histamine in human keratinocytes and fibroblasts.

BACKGROUND: Both neurotrophins and chemorepellents are involved in the elongation and sprouting of itch-associated C-fibers in the skin. Nerve growth factor (NGF) and semaphorin 3A (Sema3A) are representatives of these two types of axon-guidance factors, respectively. OBJECTIVE: We investigated the effects of calcium concentration and histamine on the expression of NGF and Sema3A in normal human epidermal keratinocytes (NHEK) and normal human fibroblasts (NHFb). METHODS: NHEK and NHFb were cultured under different calcium concentrations (0.15-0.9 mM) with or without histamine, and the expression of mRNA for NGF and SEMA3A was assessed by real-time PCR analysis. An immunohistochemical study was performed for Sema3A using normal skin and skin cancer specimens. RESULTS: In NHEK, SEMA3A expression was elevated by high calcium concentration and reduced by low calcium condition, while NGF expression was not dependent on calcium. Their expressions were unchanged by calcium in NHFb. Immunohistochemically, keratinocytes in the prickle layer of normal epidermis and squamous cell carcinoma cells were positive for Sema3A, sparing basal cells and suprabasal cells. The addition of histamine to NHEK at 10 µg/ml enhanced SEMA3A expression but depressed NGF expression. In NHFb, however, histamine decreased both NGF and SEMA3A levels. CONCLUSIONS: Sema3A inhibits C-fiber elongation/sprouting in the upper layers of the epidermis, where calcium concentration is high, thereby determining the nerve endings. Histamine reduces Sema3A production by fibroblasts, allowing C-fibers to elongate in the dermis. In contrast, the histamine-augmented keratinocyte production of Sema3A might suppress C-fiber elongation and exaggerated pruritus.

Inhibition of vascular endothelial growth factor (VEGF)-165 and semaphorin 3A-mediated cellular invasion and tumor growth by the VEGF signaling inhibitor ZD4190 in human colon cancer cells and xenografts.

We recently showed by DNA microarray analysis that vascular endothelial growth factor (VEGF) receptor (VEGFR) is expressed in HCT8/S11 human colon cancer cells, suggesting that several angiogenic factors may target colon cancer cells themselves. In this study, transcripts encoding the VEGF-165 and semaphorin 3A (Sema3A) receptors and coreceptors Flt-1, KDR/Flk-1, plexin A1, and neuropilins NP-1 and NP-2 were identified by reverse transcription-PCR in the human colon cancer cell lines HCT8/S11, HT29, HCT116, and PCmsrc. Collagen invasion induced by VEGF-165 and Sema3A in HCT8/S11 cells (EC(50), 0.4-1 nmol/L) required p42/44 mitogen-activated protein kinase and signaling through RhoA/Rho-kinase-dependent and -independent pathways, respectively. As expected, the VEGFR signaling inhibitor ZD4190 selectively abrogated the proinvasive activity of VEGF in collagen gels (IC(50), 10 nmol/L) and chick heart fragments. We identify a novel function for VEGF-165 and Sema3A as proinvasive factors for human colorectal cancer cells. Interestingly, oral administration of the single drug ZD4190 to athymic mice (50 mg/kg/d, once daily) inhibited by 70% the growth of HCT8/S11 tumor cell xenografts. Combinations between the src tyrosine kinase inhibitor M475271 and ZD4190 or cisplatin resulted in additive therapeutic activity against LNM35 human lung tumor xenografts. Our data have significant implications for new therapeutic approaches and individualized treatment targeting VEGFR and src signaling pathways in combination with established clinical drugs at primary tumors and distant metastases in colon and lung cancer patients.