Ritian Jin,Jude Juventus Aweya,Rong Lin,Wuyin Weng,Jiaqi Shang,Dangfeng Wang,Yiling Fan,Shen Yang
VLATSGPG (VLA) was a DPP-IV inhibitory peptide isolated from salmon ( Salmo Salar ) skin. Here, we demonstrated that VLA inhibited the activation of PERK through the AKT signaling pathway. Furthermore, we investigated the effect of VLA on free fatty acid (FFA)-induced lipid accumulation disorder and inflammation in HepG2 cells, elucidating the potential regulatory mechanism in this nonalcoholic fatty liver disease cell model. VLA reduced the mRNA expression of adipogenic factors FAS, ACC, and SCD-1 through the PERK/eIF2α pathway and the level of apolipoprotein B-100 secretion. These may contribute to the reducing FFA-induced lipid accumulation in cells and reducing intracellular lipid levels. In addition, VLA increased IκBα mRNA expression via the PERK/IκBα pathway, inhibited the NF-κB p65 activation, and thus inhibited cell inflammation.
Here, we characterize the activities of two depeptidyl peptidase-IV (DPP-IV) inhibitory peptides, VLATSGPG and LDKVFER, using the Caco-2 monolayer model for the intestine. VLATSGPG and LDKVFR inhibited the DPP-IV in the cells via a mixed-type inhibition mode, with in situ IC50 values of 207.3 and 148.5 μM, respectively. Furthermore, VLATSGPG and LDKVFR were transported intact across the cells, with Papp values of 2.41 ± 0.16 and 4.23 ± 0.29 × 10–7 cm/s, respectively. Fragmented peptides were identified in the basolateral side of the membrane. Two of these, GPG and VLA, exhibited high inhibitory activities of 83.6 ± 3.3 and 58.5 ± 2.5%, respectively, at 100 μM concentration. Although 3 mM VLATSGPG and LDKVFR were transported across the epithelium in a concentration-dependent manner, their transport did not damage the tight junction proteins, ZO-1 and occludin. This study demonstrates that the two peptides potentially regulate DPP-IV activity in the intestine.
Ritian Jin,Haowei Ren,Minhe Liao,Jiaqi Shang,Dangfeng Wang,Meng Li,Ning Liu
The peptide VLATSGPG (VLA) is known to inhibit dipeptidyl peptidase IV (DPP-IV), although its mechanism in relieving endoplasmic reticulum (ER) stress is unclear. In this study, we found that treating HepG2 cells with 1.0 mM VLA reduced DPP-IV activity by 73.7 ± 4.8% without changing the DPP-IV mRNA expression level. In addition, 1.0 and 0.5 mM VLA alleviated palmitic acid (PA)-induced cell death and intracellular calcium imbalances. The levels of apoptosis-related proteins (caspase-3, caspase-9, and CHOP) were reduced by VLA treatment, which was presumed to be related to ER stress. Further studies confirmed that VLA alleviated PA-induced morphological damage to the ER and reduced the levels of the ER stress marker proteins (BIP, p-PERK, and p-IRE1α). VLA alleviated PA-induced ER stress in HepG2 cells independent of DPP-IV enzymatic activity inhibition. These findings have implications for developing novel treatment approaches for liver diseases caused by ER stress.
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