TGF‐β1 potentiates astrocytic nitric oxide production by expanding the population of astrocytes that express NOS‐2

Abstract

Both transforming growth factor-beta1 (TGF-beta1) and nitric oxide synthase-2 (NOS-2) are upregulated under various neuropathological states. Evidence suggests that TGF-beta1 can either attenuate or augment NOS-2 expression, with the prevailing effect dependent on the experimental paradigm employed and the cell-type under study. The purpose of the present study was to determine the effect of TGF-beta1 on astrocytic NOS-2 expression. In purified astrocyte cultures, TGF-beta1 alone did not induce NOS-2 or NO production. However, NO production induced by lipopolysaccharide (LPS) plus IFNgamma was enhanced by TGF-beta1 in a concentration-dependent manner between 10 and 1,000 pg/mL. The presence of IFNgamma was not necessary for this effect to occur, as TGF-beta1 enhanced NO production induced by LPS in a similar fashion. In cultures stimulated with LPS plus IFNgamma, the enhancement of NO production by TGF-beta1 was associated with a corresponding increase in NOS-2 mRNA and protein expression. Interestingly, immunocytochemical assessment of NOS-2 protein expression demonstrated that TGF-beta1 augmented astrocytic NO production, specifically by increasing the pool of astrocytes capable of expressing NOS-2 induced by either LPS (approximately threefold) or LPS plus IFNgamma (approximately sevenfold). In a broader sense, our results suggest that TGF-beta1 recruits a latent population of astrocytes to respond to stimulation by pro-inflammatory mediators.

TGF-β1 reduces the heterogeneity of astrocytic cyclooxygenase-2 and nitric oxide synthase-2 gene expression in a stimulus-independent manner

“…We demonstrated previously that treatment with TGF-β1 enhances astrocytic nitric oxide production induced by LPS plus interferon-γ (IFNγ) by increasing the number of astrocytes in a population that express NOS-2 [14]. To test whether TGF-β1 augments COX-2 expression in murine astrocytes, COX-2 mRNA and protein expression were examined in murine primary astrocyte cultures by qRT-PCR and Western blot analysis, respectively.…”

“…Protein lysates were generated from cell cultures as previously described [14]. Protein concentrations were determined using the BCA Assay (Pierce).…”

Over-production of nitric oxide by oxidative stress-induced activation of the TGF-β1/PI3K/Akt pathway in mesangial cells cultured in high glucose

“…TGF-β1 is required for NF-kappaB-mediated modulation of iNOS activity when controlling the induction of the Epstein-Barr virus replication cycle [40] . A report showed that TGF-β1 stimulates NO production in astrocytes by recruiting distinct cell subpopulations [41] . Therefore, the iNOS expression induced by the TGF-β1/PI3K/Akt pathway may be a main reason for NO over-production in MCs cultured in high glucose ( Figure 6).…”

The role of the JAK-STAT pathway in neural stem cells, neural progenitor cells and reactive astrocytes after spinal cord injury

“…Reactive astrocytes can preserve neurons and oligodendrocytes, and protect motor functions after SCI (72,76,78), potentially due to the astrocyte-secretory polypeptides (astrocyte-derived cytokines and trophic factors), which alter the microenvironment (83)(84)(85). These cytokines include IL-1β, TNF-α, IL-6, IL-11 and transforming growth factor-β1 (86)(87)(88)(89)(90)(91)(92) and the trophic factors include brain-derived neurotrophic factor, glial cell line-derived neurotrophic factor, nerve growth factor (NGF), CNTF, basic fibroblast growth factor and leukemia inhibiting factor (LIF) (93)(94)(95)(96)(97). Recently, increasing evidence has indicated that cytokines and trophic factors secreted by reactive astrocytes may protect the injured tissues and cells through the JAK-STAT pathway (82,98).…”