AD has been well known as a proteopathy disease which caused by formation of Aβ plaqueand tau tangles in the brain (
36). In addition to Aβ plaque, there are toxic oligomers of Aβ that bind to neuronal surface receptors. These interactions play important roles in loss of neurons connections (
37,
38). On the other hand, tauopathy fragmentize the neuron's transport system (
39), so the researchers are interested to reduction of amyloid levels, prevention of amyloid aggregation/toxicity and tau phosphorylation/aggregation. Since several different proteins, such as APP, APOE, BACE (Aβ cleaving enzyme), PS1/2, secretases, and tau play important roles in the pathology of AD, Therefore, inhibition of BACE, PS-1 and g-secretase are important activities in treatment of AD. A number of strategies such as acetylcholinesterase inhibitors, anti-oxidants, anti-inflammatory agents, hormone therapy, cholesterol-lowering agents and vaccination, are being investigated for treating or slowing the progression of AD (
1-
6). Today, herbal treatments as mainly alternative medicine for Alzheimer's are widely expanded. Here, neuroprotective mechanism of LE wasinvestigated by proteomics approach. Previously determined that such protective effect might be related to antiglutamatergic, calcium channel blocking and antioxidant activity (
24,
40,
41). These pharmacologic activities of lavender linked to presence of a lot of monoterpenes (especially linalyl acetate, linalool) (
22,
42). Proteomics act as effective target discovery system that applied to rapid identification of proteins, which are likely to be targets for therapeutic development. As represented in
Figure 1, the analysis of hippocampal proteome determined some proteins with different expression level in three groups (N, Aβ and Aβ+LE).
These proteins belong to the biological process correlate neuroprotective effect of LA tomake removing Aβ plaques or restructuring AD neurons after treatment with LE. These proteins included Snca, Hspa, Prdx2, Apoa1, Atp5a1 and NF-L which comprehensively are explained in table 1. Protein–protein interaction as a powerful proteomic activity is applied for interpretation of interactions of these proteins to each other's. Beside on, the brain function likewise other organs can be explained by protein complexes in different terms such as the number, type and location. Protein networks analysis by proteomics tools can help to description of neurobiological phenomena (
43). In addition to, co-expression patterns of genes displaying as gene set, protein complex or part of a functionally related pathway, so in this study proteins are studied in network models for more resolution.
Alpha-synuclein (Snca), the most important protein in this study, is aprotein whose accumulation is common to many neurodegenerative diseases (
44), and it is non-Aβ component in AD amyloid that modulates the APP mRNA. This protein is found only in brain (hippocampus, brain stem and cortex). Snca is tau protein binding and can interact significantly with tubulin (
45,
46), and it is also acts as a molecular chaperone in configuration of SNARE complexes (
47,
48). Several Yeast genes in lipid metabolism display in Snca toxicity (
49) in contrary its possible antioxidant activity (
50). Since Snca specifically expressed in neuronal cell bodies and synapses, it may be involved in the regulation of dopamine release and transport phenomena, so that has been reported to accumulate abnormally in AD, PD and inflammatory demyelinating disease (
44). Additionally, mutations in Snca were found to be associated with rare familial cases of early-onset of PD (
51,
52). Amongst many versatile functions of Snca, it has been mainly described to beinvolved in the regulation of membrane stability and/or turnover and display in synapse, axon, synaptosome, clathrin-coated vesicle, and cellular response to oxidative stress. Binding proteins (
Figure 2a), like Bad, have been identified as Snca target (
35).Bad (Bcl2 antagonist of cell death) that responses to reactive oxygen species acts in different pathways such as ErbB signaling pathway and apoptosis, which have been extensively described in the context of AD. In this context, interactions with PD associated proteins like leucine-rich repeat kinase 2 (Lrrk2), Protein DJ-1 (Prkce) and Tyrosine3-monooxygenase (Th) may lead in neuron development and differentiation associated with lavender treatment (
53,
54). In this study, additional isoforms of Snca seem to exist with different expression while previously specified increasing level of Snca in AD (
55). Snca levels were significantly reduced in aged condition in all structures except hippocampus while up-regulated in presynaptic terminals during synaptic rearrangement (
56). However, here, up-regulation of several isoforms of Snca was detected in treated with LE sample. Based on conflicting evidences, Snca is associated with a non-apoptotic de novo expression after axotomy of adult rat that shown slow form of neurodegeneration in facial motor neurons (
57). Besides, pro-apoptotic function in AD pathogenesis, de novo over-expression of Snca in hippocampus neuron after treatment with LA have a number of its neuroprotective effects such as tau substitution act in cellular transport, cellular localization,vesicle trafficking, membrane stability, cooperation with clathrin and amphiphysin to increase endocytosis, regulation of neurotransmitter transport, membrane depolarization, positive regulation of transmission of nerve impulse, regulation of post synaptic membrane potential, and finally act as oxidoreductase and antioxidant enzyme.
Heat shock protein 5 (Hspa5) belongs to the heat shock protein 70 family and displays in protein complex assembly inside the ER (
58). It was determined regulatory role of HSPA5 in the stress response (
59). It also is anti-apoptotic protein display in prion diseases (
Figure 2b) related to proteins such as Eif2ak3 and Creb1. Biological process of Eif2ak3 is regulation of nervous system development and demonstrates in AD, whereas Creb1 be involved in the neuron differentiation and neuron projection development and display in HD (
35). In this study, Hspa5 had 2.5 fold more expressionin the presence of lavender while in AD has even lower expression than normal hippocampus. Hspa5 as a heat shock protein implies its neuroprotective function that may be relate to anti-apoptotic protection of LA.
Mitochondrial membrane ATP synthase (Atp5a1) is a protein in respiratory chain deal with generation of ATP from ADP (
35), it binds to Atp5b, Atp5d,Atp5o, ATP6, Atp5f1, Atp5j, Atp5c1, Atp5i, Ndufv1, Atp5g1(
Figure 2c). All of interacted proteins except Atp5i are composed of pathways like oxidative phosphorylation, AD, PD, HD (
35). Beforehand Tsuji T
et al. (
60) determined decreasing amount of Atp5a1 in AD, but in our study, increased expression of Atp5a1 in AD group than the two other groups was seen.
Neurofilament light polypeptide (NF-L) is a member of the actin proteinand intermediate filament (IF). IFs are primordial components of cytoskeleton and nuclear envelope. It seems that level of IF gene expression directly controls axonal diameter, which in turn controls how fast electrical signals travel down the axon. IFs are subdivided into three major subgroups IF- L, M, and H which are involved in the maintenance of neuronal caliber (
61-
63). NF-L (
Figure 2d) binds to Mapk12 (mitogen-activated protein kinase 12), Mapk13, Mapk14, Nefh (neurofilament), Nefm, Prph (peripherin) and Prph2 which are involved in pathway associated to Amyotrophic Lateral Sclerosis (ALS). Sod1, superoxide dismutase 1 that is related to ALS is composed to HD and Prion diseases (
35). Increment of NF-L level was specified in AD (
64), in this study LA lead to 3.7 fold more expression than the other two groups. This effect may be related to microtubule cytoskeleton organization, regulation of neurogenesis and prevents, or reduces the frequency, rate orextent of cell death by apoptotic process (
35).
Thioredoxin peroxidase 1 (Prdx2, TDX1) is an antioxidant protein involvedin cellular redox regulation. By reducing peroxides through thioredoxin system may act to get rid of peroxides generated during metabolism. It might also regulate the intracellular concentrations of H
2O
2 or involved in the neurotrophic process (
65). It binds to proteins Atp5h and Atp5o (
Figure 2e) that are in oxidative phosphorylation, AD, PD, HD, Park7 (peroxiredoxin activity) in PD, Cat in ALS, Sod1 in ALS, HD and Priondiseases and Sod2 in HD (
35). It is reported that its expression increasesin AD (
66) but here we found down regulated in AD than the two other groups and LE causes increasing Prdx2 expression to 2.8 fold.
Apolipoprotein A-I (ApoA-I), the major protein of high-density lipoprotein(HDL), belongs to the apolipoprotein A1/A4/E family takes part in the cholesterol reverse transport from tissues to the liver for excretion. It also exhibits its anti-inflammatory activity in inflammatory responses. As renal inflammation it plays an important role in ischemia/reperfusion (I/R) injury of the kidney. ApoA-I improved renal function by decreasing I/R-induced inflammatory responses such as inhibition release of inflammatory cytokines and neutrophil infiltration and activation (
67). It binds Carkd, Tmem160, RGD1309998, Exosc4, Fdx1l, LOC687308, Nudt14, Mrpl28, Mrps23 and Mrps33, (
Figure 2f) that all of them are located in mitochondria (
35). Previous investigation assigned decreasing ApoA-I in AD (
68), but here seen increases to 1.6 fold in AD that might be affiliated to its anti-inflammatory activity.
Previous study illustrated the protective effect of aqueous extract of lavender on eliminating Aβ in in trahippocampal Aβ-injected rat model of AD (
20,
30), here we evaluated the mechanism of this beneficial effect related to expression some protective proteins such as Snca, Hspa, Prdx2, Apoa1, Atp5a1 and NF-L as protein target for monoterpen agents (rosmarinic acid, caffeic acid, luteolin 7-Oglucoside,methyl carnosoate (
69)) in LA that trigger mechanisms such as anti-lipid peroxidation, antiglutamatergic and anti-inflammatory activities (
69).