br Introduction Free fatty acids FFAs including saturated an

Introduction Free fatty acids (FFAs), including saturated and unsaturated FFAs, are the major source of lipid energy in human body and released mainly from adipose tissue by lipolysis of triglycerides (Miles and Nelson, 2007). FFAs circulating in the plasma are largely bound to the albumin, with a concentration of ~0.1 to 1.0mM. Lipotoxicity follows when non-adipose cells are exposed to chronic elevation of FFAs, which can result from disturbed balance between release and clearance of FFAs, e.g., on a high fat diet or under other metabolic conditions (Mittendorfer, 2011; Boden, 2008). Besides fatty acids trafficking alterations, high level of FFAs may also be a consequence of membrane phospholipid degradation caused by activated phospholipases in many pathological conditions, such as trauma, hypoxia and stroke (Farooqui and Horrocks, 1998). It has been reported that FFAs accumulated acutely after traumatic brain injury, with the concentration of palmitic oxyntomodulin cost (PA) in the brain increasing from ~60 to 180μM and stearic acid (SA) from ~50 to 350μM (Lipton, 1999). Moreover, elevated plasma FFA level can inhibit insulin\'s anti-lipolytic action which further increases the release of FFAs into circulation (Boden, 2008). Pathological accumulation of saturated FFAs in the human body can pose serious threat to normal cellular homeostasis, which has been suggested to be involved in the development of many chronic diseases, such as obese, diabetes and cardiovascular diseases (Gomez-Lechon et al., 2007; Saunders et al., 2008). Importantly, brain could uptake FFAs from plasma through the blood–brain barrier (Wang et al., 1994). In other words, elevated FFA level can exacerbate cellular damage directly on brain, leading to different extent of cognitive decline and brain abnormalities (Adibhatla and Hatcher, 2008). In addition, excessive saturated FFAs could freely penetrate placental barrier, thereby interfering with the development and growth of embryos, including the development of brain (Yu et al., 2009; Elahi et al., 2009; Tozuka et al., 2009). These data suggest that FFAs can readily enter and exert their destructive effects on the brain. There is growing evidence indicating that the deleterious effects of saturated FFAs on the brain have been associated with alterations of its cells. Cell death was obvious when nerve growth factor-differentiated PC12 cells were exposed to FFAs, such as SA and PA (Ulloth et al., 2003; Almaguel et al., 2009). FFAs exerted Alzheimer-like pathological effects on neurons through their actions on primary rat cortical astroglia (Patil et al., 2007). Neural stem cells (NSCs), residing in both fetal and adult brain, have been suggested to differentiate into various kinds of neurons and astrocytes and play important roles in the development and injuries repair of the brain (Temple, 2001; Alvarez-Buylla et al., 2002; Kim, 2004). Many factors have been shown to exert their effects on NSCs, influencing their proliferation, apoptosis and differentiation (Gao and Gao, 2007; Anthony et al., 2008). However, there is an apparent lack of information about the effects of saturated FFAs on NSCs. In view of this, it is desirable to explore the effects of elevated saturated FFAs on NSCs, as this might offer a possible explanation for the cognitive alterations and brain abnormalities of neurological disorders due to elevation of FFAs. In the present study, we have employed suspension culture to obtain mouse NSCs in vitro in the form of neurospheres. We next investigated the impact of PA, the most abundant saturated fatty acid in the diet or in the plasma, on NSCs in vitro with an aim to gain a further understanding of the underlying molecular mechanism of its effects on the stem cells.
Materials and methods
Results
Discussion Elevated FFA level has been associated with the development of many pathological conditions including neurological disorders. For instance, elevation of FFAs has been suggested to be a risk factor of Alzheimer\'s disease, with neurons and astrocytes being affected, which might be responsible for the cognitive decline in the brain (Patil et al., 2006, 2008). Cognitive abilities, such as learning and memory, depend on neurogenesis in the brain, which is involved in the proliferation, apoptosis and differentiation of NSCs and can be influenced by many stimuli (Fike, 2011; Tesone-Coelho et al., 2012; Lindqvist et al., 2006; Gao and Gao, 2007). Plasma saturated FFAs, such as SA and PA, could bring about deleterious effects on many cell types, with apoptosis being the most common phenomenon (Jiang et al., 2010; Wang et al., 2010; Malhi et al., 2006; Welters et al., 2006; Almaguel et al., 2009; Ricchi et al., 2009). Therefore, it is worthy to explore whether elevated saturated FFA level would also influence the apoptosis of NSCs. In the present study, we have chosen PA as a representative saturated fatty acid, to explore its effects on NSCs.