Decreased FABP5 and DSG1 protein expression following PAX6 knockdown of differentiated human limbal epithelial cells.

PAX6 haploinsufficiency related aniridia is characterized by disorder of limbal epithelial cells (LECs) and aniridia related keratopathy. In the limbal epithelial cells of aniridia patients, deregulated retinoic acid (RA) signaling components were identified. We aimed to visualize differentiation marker and RA signaling component expression in LECs, combining a differentiation triggering growth condition with a small interfering RNA (siRNA) based aniridia cell model (PAX6 knock down). Primary LECs were isolated from corneoscleral rims of healthy donors and cultured in serum free low Ca2+ medium (KSFM) and in KSFM supplemented with 0.9 mmol/L Ca2+. In addition, LECs were treated with siRNA against PAX6. DSG1, PAX6, KRT12, KRT 3, ADH7, RDH10, ALDH1A1, ALDH3A1, STRA6, CYP1B1, RBP1, CRABP2, FABP5, PPARG, VEGFA and ELOVL7 expression was determined using qPCR and western blot. DSG1, FABP5, ADH7, ALDH1A1, RBP1, CRABP2 and PAX6 mRNA and FABP5 protein expression increased (p ≤ 0.03), PPARG, CYP1B1 mRNA expression decreased (p ≤ 0.0003) and DSG1 protein expression was only visible after Ca2+ supplementation. After PAX6 knock down and Ca2+ supplementation, ADH7 and ALDH1A1 mRNA and DSG1 and FABP5 protein expression decreased (p ≤ 0.04), compared to Ca2+ supplementation alone. Using our cell model, with Ca2+ supplementation and PAX6 knockdown with siRNA treatment against PAX6, we provide evidence that haploinsufficiency of the master regulatory gene PAX6 contributes to differentiation defect in the corneal epithelium through alterations of RA signalling. Upon PAX6 knockdown, DSG1 differentiation marker and FABP5 RA signaling component mRNA expression decreases. A similar effect becomes apparent at protein level though differentiation triggering Ca2+ supplementation in the siRNA-based aniridia cell model. Expression data from this cell model and from our siRNA aniridia cell model strongly indicate that FABP5 expression is PAX6 dependent. These new findings may lead to a better understanding of differentiation processes in LECs and are able to explain the insufficient cell function in AAK.

In Silico Identification of Novel Interactions for FABP5 (Fatty Acid-Binding Protein 5) with Nutraceuticals: Possible Repurposing Approach.

Fatty Acid Binding-Protein 5 (FABP5) is a cytoplasmic protein, which binds long-chain fatty acids and other hydrophobic ligands. This protein is implicated in several physiological processes including mitochondrial ß-oxidation and transport of fatty acids, membrane phospholipid synthesis, lipid metabolism, inflammation and pain. In the present study, we used molecular docking tools to determine the possible interaction of FABP5 with six selected compounds retrieved form Drugbank. Our results showed that FABP5 binding pocket included 31 polar and non-polar amino acids, and these residues may be related to phosphorylation, acetylation, ubiquitylation, and mono-methylation. Docking results showed that the most energetically favorable compounds are NADH (-9.12 kcal/mol), 5'-O-({[(Phosphonatooxy)phosphinato]oxy}phosphinato)adenosine (-8.62 kcal/mol), lutein (-8.25 kcal/mol), (2S)-2-[(4-{[(2-Amino-4-oxo-1,4,5,6,7,8-hexahydro-6-pteridinyl)methyl]amino}benzoyl)amino]pentanedioate (-7.17 kcal/mol), Pteroyl-L-glutamate (-6.86 kcal/mol) and (1S,3R,5E,7Z)-9,10-Secocholesta-5,7,10-triene-1,3,25-triol (-6.79 kcal/mol). Common interacting residues of FABP5 with nutraceuticals included SER16, LYS24, LYS34, LYS40 and LYS17. Further, we used the SwissADME server to determine the physicochemical and pharmacokinetic characteristics and to predict the ADME parameters of the selected nutraceuticals after molecular analysis by docking with the FABP5 protein. Amongst all compounds, pteroyl-L-glutamate is the only one meeting the Lipinski's rule of five criteria, demonstrating its potential pharmacological use. Finally, our results also suggest the importance of FABP5 in mediating the anti-inflammatory activity of the nutraceutical compounds.

Clinical relevance of gene expression in localized and metastatic prostate cancer exemplified by FABP5.

PURPOSE: Fatty acid-binding protein 5 (FABP5), a transport protein for lipophilic molecules, has been proposed as protein marker in prostate cancer (PCa). The role of FABP5 gene expression is merely unknown. METHODS: In two cohorts of PCa patients who underwent radical prostatectomy (n = 40 and n = 57) and one cohort of patients treated with palliative transurethral resection of the prostate (pTUR-P; n = 50) FABP5 mRNA expression was analyzed with qRT-PCR. Expression was correlated with clinical parameters. BPH tissue samples served as control. To independently validate findings on FABP5 expression, three microarray and sequencing datasets were reanalyzed (MSKCC 2010 n = 216; TCGA 2015 n = 333; mCRPC, Nature Medicine 2016 n = 114). FABP5 expression was correlated with ERG-fusion status, TCGA subtypes, cancer driver mutations and the expression of druggable downstream pathway components. RESULTS: FABP5 was overexpressed in PCa compared to BPH in the cohorts analyzed by qRT-PCR (radical prostatectomy p = 0.003, p = 0.010; pTUR-P p = 0.002). FABP5 expression was independent of T stage, Gleason Score, nodal status and PSA level. FABP5 overexpression was associated with the absence of TMPRSS2:ERG fusion (p < 0.001 in TCGA and MSKCC). Correlation with TCGA subtypes revealed FABP5 overexpression to be associated with SPOP and FOXA1 mutations. FABP5 was positively correlated with potential drug targets located downstream of FABP5 in the PPAR-signaling pathway. CONCLUSION: FABP5 overexpression is frequent in PCa, but seems to be restricted to TMPRESS2:ERG fusion-negative tumors and is associated with SPOP and FOXA1 mutations. FABP5 overexpression appears to be indicative for increased activity in PPAR signaling, which is potentially druggable.