PNPLA3, the triacylglycerol synthesis/hydrolysis/storage dilemma, and nonalcoholic fatty liver disease

Table 1 Patatin-like phospholipase domain containing 3 protein features and functions

PNPLA3 belongs to the IPLA2/lipase family. The protein encoded by PNPLA3 is a triacylglycerol lipase that mediates triacylglycerol hydrolysis in adipocytes. Multifunctional enzyme that has both triacylglycerol lipase and acylglycerol O-acyltransferase activity (http://genatlas.medecine.univ-paris5.fr/)

Lipid hydrolase with an unusual folding topology that differs from classical lipases[38]

The enzyme is highly regulated by changes in energy balance: nutritional control of PNPLA3 being affected by a feed-forward loop[36]

PNPLA3 mRNA increases during differentiation of rat adipocytes in an insulin-dependent manner[39]

PNPLA3 mRNA expression is upregulated by tri-iodothyronine in adipocytes in vitro, in humans and rats, and in vivo in rat WAT[39]

PNPLA3 mRNA expression is upregulated by tri-iodothyronine in adipocytes in vitro, in humans and rats, and in vivo in rat white adipose tissue[40]

Promoter region of the human adiponutrin/PNPLA3 gene is regulated by glucose and insulin[33]

Fasting significantly downregulates PNPLA3 mRNA expression in liver and adipose tissue[35]

Feeding significantly upregulates PNPLA3 mRNA in liver and fat[34]

Liver PNPLA3 mRNA is expressed in human liver in higher levels compared with adipose tissue[36]

PNPLA3 mRNA is highly expressed in liver of b/ob mice[40] and visceral and subcutaneous adipose issue in obese humans[41]

PNPLA3 mRNA is expressed in hepatocytes but not in Kupffer cells[35,36]

PNPLA3 is expressed in hepatocytes but not in liver endothelial and Kupffer cells; microarray-based gene profiling showed that the expression level of

PNPLA3 in hepatocytes is correlated with that of genes associated with the lipogenic pathway such as ME1, SPOT14, and SCD1[35]

PNPLA3 is regulated in human hepatocytes by glucose via ChREBP[42]

SREBP1c is able to induce PNPLA3 expression in human immortalized hepatocytes and in HepG2 hepatoma cells[37]

PNPLA3: Patatin-like phospholipase domain containing 3; SREBP1c: Sterol regulatory element binding protein 1; ChREBP: Carbohydrate-responsive element-binding protein; ME1: Malic enzyme; SCD1: Stearoyl-CoA desaturase 1.

Table 2 In silico prediction of rs738409 C or G alleles as putative and differential target sites of microRNA

rs738409-C miRNA	rs738409-G miRNA
hsa-miR-1233	hsa-miR-1181, hsa-miR-1295, hsa-miR-1298, hsa-miR-133a, hsa-miR-133b
hsa-miR-1249	hsa-miR-135a, hsa-miR-136, hsa-miR-139-5p, hsa-miR-190b, hsa-miR-222
hsa-miR-129-5p	hsa-miR-297, hsa-miR-324-5p, hsa-miR-331-5p, hsa-miR-34c-5p, hsa-miR-362-5p
hsa-miR-155	hsa-miR-370, hsa-miR-370, hsa-miR-376b, hsa-miR-384, hsa-miR-412, hsa-miR-432
hsa-miR-365	hsa-miR-449a, hsa-miR-449b, hsa-miR-452, hsa-miR-455-5p, hsa-miR-509-3-5p
hsa-miR-433	hsa-miR-511, hsa-miR-513a-5p, hsa-miR-513b, hsa-miR-515-3p, hsa-miR-516a-3p
hsa-miR-498	hsa-miR-516b, hsa-miR-518d-5p, hsa-miR-519b-5p, hsa-miR-519c-5p, hsa-miR-519e
hsa-miR-517a	hsa-miR-526a, hsa-miR-550, hsa-miR-552, hsa-miR-554, hsa-miR-557, hsa-miR-579
hsa-miR-517c	hsa-miR-582-5p, hsa-miR-584, hsa-miR-593, hsa-miR-600, hsa-miR-600, hsa-miR-601
hsa-miR-578	hsa-miR-609, hsa-miR-613, hsa-miR-623, hsa-miR-623, hsa-miR-623, hsa-miR-629
hsa-miR-586	hsa-miR-632, hsa-miR-636, hsa-miR-642, hsa-miR-642, hsa-miR-654-5p, hsa-miR-659
hsa-miR-874	hsa-miR-661, hsa-miR-663b, hsa-miR-664, hsa-miR-668, hsa-miR-760, hsa-miR-875-5p

Prediction was assessed by PITA miRNA prediction tool. Each allele was represented by at least 60 bp around the polymorphic base using a seed of 7 bp.

Table 3 Results of search for miRNA target sites on the 3’ untranslated region of the patatin-like phospholipase domain containing 3 gene by DIANA-microT v3.0 prediction tool

miRNA name	Binding category	UTR start	UTR stop	UTR binding NTs
hsa-miR-769-3p	8mer (pos 1)	89	117	GCC GAC U G GGAUCCCAG
hsa-miR-769-3p	7mer (pos 2)	389	417	GAGA GAUCCCA
hsa-miR-769-3p	7mer (pos 1)	699	727	G CAG GGC CGG AUCCCAG
hsa-miR-769-3p	7mer (pos 1)	834	862	G CA CCUG AUCCCAG
hsa-miR-516a-3p	8mer (pos 1)	128	156	UGAA AGGAAGCA
hsa-miR-516a-3p	7mer (pos 2)	216	244	GCU UUGGG AGGAAGC
hsa-miR-516a-3p	8mer (pos 2)	591	619	UG AAGGAAGC