## 4 Discussion  
Our previous work reported the ability of curcumin to reduce the TG2 overexpression induced by retinoic acid in human nervous cell lines [25]. On the basis of these previous data, and other data present in the literature, we analyzed the effects of curcumin and of another nutraceutical with known anti-inflammatory properties, such as PEA, on the TG2 expression in mouse microglial cells. The present study provides the evidence that curcumin, a naturally occurring compound derived from turmeric (Curcuma longa) that has long been suggested to have strong therapeutic or preventive potential against several major human diseases because of its anti-oxidative, anti-cancerous and anti-inflammatory effects, and the endocannabinoid PEA, are capable of down-regulating the lipopolysaccharide- or amyloid-\(\beta\) 1-42 peptide-induced overexpression of TG2 in mouse microglial cells. In fact, we found that, similarly to curcumin, PEA exerted protective effects on microglia cells. The anti-inflammatory and neuroprotective effects of PEA have been largely demonstrated in different neuroinflammatory conditions associated with CNS disorders [32; 33]. This effect was associated with the reduction in an inflammatory cell phenotype, as suggested by the reduction in the proinflammatory markers and the increase in the typical anti-inflammatory markers of microglia. TG2 is both an intracellular and extracellular transglutaminase found in many cells and tissues [3] and is involved in several physiological processes, such as apoptotic cell death [4; 5; 6], in which the enzyme is induced and activated in apoptotic cells, and cross-linked proteins accumulate in the fragments (apoptotic bodies) of cells undergoing programmed cell death [7; 8]. Recently, the data from numerous studies have demonstrate the involvement of TG2 in Celia disease (CD), while more recently, a large body of literature has suggested that TG2 could be involved in neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease (PD) and other neurodegenerative diseases [18; 19]. Moreover, it has also been suggested that this enzyme has a possible role in the neuroinflammation process, which is often present during these neurodegenerative disorders [20]. Significantly, curcumin is known to exert anti-inflammatory effects by interrupting NF-kB signaling at multiple levels, very likely by inhibiting the activity of the inhibitor of NF-kB kinase (IKK). In fact, many observations indicate that curcumin indeed shows valuable potential in cancer treatment through inhibiting the activity of I-kB kinase, IKK [21]. Since data from the literature have suggested that TG2 activates the pro-inflammatory transcriptional factor NF-kB  
Figure 7: Panel (**A**): Western blot for TG2 expression. BV2 cells were cultured in medium supplemented or not with 10 uM of PEA or Cu, and A\(\beta\)1-42 (1 uM) for 48 h. SDS-PAGE was blotted with antibody against TG2. GAPDH protein expression was used as loading control. The experiments were performed at least 3 different times and the results were always similar; Panel (**B**): graph shows the densitometric intensity the full lanes (TG2 full length and splicing variants)/GAPDH bands ratio. # \(p\) value \(<\) 0.05 compared with control group (NT). ## _p_\(<\) 0.05 compared with A\(\beta\)1-42 group. in multiple ways, either by inducing the polymerization of its inhibitory subunit I-kB\(\alpha\), which, in turn, results in the dissociation of NF-kB and its translocation to the nucleus, where it is capable of up-regulating host inflammatory genes [22], or by a non-canonical pathway [23], and, on the other side, NF-kB regulatory response elements are also present in the transglutaminase 2 promoter [24], we analyzed the effects of curcumin and the endocannabinoid PEA on TG2 expression in murine microglial cells. In fact, most of the anti-inflammatory effects of PEA have been attributed to the activation of peroxisome proliferatorator-activated receptor-alpha (PPAR-\(\alpha\)) [34].