Sphingosine Kinase 1 Regulates Differentiation of Human and Mouse Lung Fibroblasts Mediated by TGF-β1

Abstract

Transforming growth factor beta (TGF-beta) contributes to the progression of pulmonary fibrosis through up-regulation of alpha-smooth muscle actin (alpha-SMA) as lung myofibroblast differentiation. Bioactive sphingosine 1-phosphate (S1P) has been shown to mimic TGF-beta signals; however, the function of S1P in lung fibrotic process has not been well documented. We found, in a mouse model of bleomycin lung fibrosis, that SPHK1 and alpha-SMA were colocalized within lung fibrotic foci and that these expressions were significantly increased in primary cultured fibroblasts. Using human lung fibroblasts WI-38, we explored the rationale of sphingosine kinase (SPHK) with TGF-beta1 stimulation. SPHK inhibitors and small interference RNA (siRNA) targeted SPHK1 decreased alpha-SMA and fibronectin expression up-regulated by TGF-beta1. In the meantime, SPHK1 inhibition did not affect smad2 phosphorylation in response to TGF-beta1. Then we examined whether S1P receptors transactivation may affect TGF-beta signals. siRNA against S1P(2) and S1P(3), but not S1P(1), reduced alpha-SMA expression as well as Y-27632, Rho kinase inhibitor. We also detected activation of Rho GTPase upon stimulation of TGF-beta1 on the cell membrane where S1P(2) or S1P(3) was overexpressed. These data suggested that SPHK1 activation by TGF-beta1 leads to Rho-associated myofibroblasts differentiation mediated by transactivated S1P receptors in the lung fibrogenic process.

Inhibition of serine palmitoyltransferase delays the onset of radiation-induced pulmonary fibrosis through the negative regulation of sphingosine kinase-1 expression

“…9A ). Next, and in concert with previous fi ndings (36)(37)(38), SphK1 was confi rmed to mediate TGF-␤ -induced signaling in nHLFB. In these cells, the downregulation of SphK1 expression by SphK1 siRNA substantially decreased TGF-␤ -induced ␣ -SMA expression ( Fig.…”

“…This may appear to contradict our earlier fi ndings; however, radiation pneumonitis and RIF are time-separate events with no active fi brogenesis going on at the pneumonitis stage of RILI. In fact, current fi ndings are well supported by the known profibrotic (36)(37)(38) and proliferative ( 40,42,43 ) role for the SphK1-S1P signaling axis, refl ecting the increased remodeling, the hallmark of fi brogenesis, in RIF lungs.…”

“…2 ). Interestingly, the link between the inhibition of SPT and the delay in RIF progression seems to converge at SphK1, the enzyme that is known to be induced by TGF-␤ and is critical for fi broblast differentiation and fi brogenesis (36)(37)(38). We show here a substantial upregulation of SphK1 expression and activity and elevated levels of DHS1P and S1P in the lung tissue and plasma in RIF mice, with myriocin being able to decrease the observed RIF-associated changes in all those parameters.…”

Thematic Review Series: Sphingolipids. Cross-talk at the crossroads of sphingosine-1-phosphate, growth factors, and cytokine signaling*

“…The prolonged activation of SphK1 plays a role in TGFb induction of TIMP-1 mRNA. SphK1 expression in myofibroblasts was also increased by TGFb (47). Interestingly, TGFb also induced a rapid increase in intracellular S1P in these cells (47), suggesting that TGFb regulation of SphK1 may also occur both transcriptionally and posttranslationally.…”

“…TGFb is important for progression of pulmonary fibrosis. TGFb stimulates SphK1, leading to an increase in S1P that in turn binds to its receptors, leading to upregulation of asmooth muscle actin expression, which is involved in the lung fibrogenic process (47) (Fig. 3).…”