👤 Takashi Ohama

Postprandial hypertriglyceridemia (PHTG) is an independent risk factor for coronary heart diseases. PHTG exhibits accumulation of apoB-48 containing chylomicron remnants (CM-Rs) and apoB-100 containing VLDL remnants (VLDL-Rs), which are both known to be atherogenic. However, unlike VLDL-Rs, structural and functional characterization of CM-Rs remains to be elucidated due to challenges in separating CM-Rs from VLDL-Rs. Recently, we successfully isolated CM-Rs and VLDL-Rs utilizing anti-apoB-48 or apoB-100 specific antibodies. This study aimed to characterize the proteome of CM-Rs along with that of VLDL-Rs. Eight healthy subjects were enrolled. Venous blood was drawn 3 hours after high-fat-containing meals. We isolated CM-Rs and VLDL-Rs from sera through combination of ultracentrifugation and immunoprecipitation using apoB-48 or apoB-100 specific antibodies, followed by shotgun proteomic analysis. We identified 42 CM-Rs or VLDL-Rs-associated proteins, including 11 potential newly identified proteins such as platelet basic protein (PPBP) and platelet factor 4, which are chemokines secreted from platelets. ApoA-I, apoA-IV, and clusterin, which are also known as HDL-associated proteins, were significantly more abundant in CM-Rs. Interestingly, apoC-I, which reduces the activity of lipoprotein lipase and eventually inhibits catabolism of remnant proteins, was also more abundant in CM-Rs. Moreover, we identified proteins involved in complement regulation such as complement C3 and vitronectin, and those involved in acute-phase response such as PPBP, serum amyloid A protein 2, and protein S100-A8, in both CM-Rs and VLDL-Rs. We have firstly characterized the proteome of CM-Rs. These findings may provide an explanation for the atherogenic properties of CM-Rs. Show less

Colorectal cancer (CRC) remains a significant global health concern, demanding a more profound comprehension of its molecular foundations for the development of improved therapeutic strategies. This study aimed to elucidate the role of protein phosphatase 6 (PP6), a member of the type 2A protein phosphatase family, in CRC. Protein phosphatase 6 functions as a heterotrimer with a catalytic subunit (PP6c), regulatory subunits (PP6Rs; PP6R1, PP6R2, and PP6R3), and scaffold subunits (ANKRD28, ANKRD44, and ANKRD52). Elevated PP6c expression has been identified in CRC tissues compared to normal mucosa, aligning with its potential involvement in CRC pathogenesis. PP6c knockdown resulted in decreased colony-forming ability and in vivo proliferation of various CRC cell lines. Transcriptome analysis revealed that PP6c knockdown resulted in altered expression of genes associated with cancer stemness. Notably, the PP6c-PP6R3 complex is a key player in regulating cancer stem cell (CSC) markers. Additionally, increased PP6c expression was observed in CSC-like cells induced by sphere formation, implicating the role of PP6c in CSC maintenance. This study highlights the role of PP6c in CRC and suggests that it is a potential therapeutic target disrupting a pathway critical for CRC progression and stem cell maintenance. Show less

We previously reported that the patients with cholesteryl ester transfer protein (CETP) deficiency (CETP-D) show marked changes in the size and lipid compositions of high-density lipoprotein (HDL) and that they are not protected from atherosclerotic cardiovascular diseases, despite increased serum HDL-cholesterol (HDL-C) levels. HDL particles carry a variety of proteins, some of which are known to have antiatherogenic functions. This study aimed to investigate the protein composition of HDL particles in patients with CETP-D. Eight patients with complete deficiency of CETP and 8 normolipidemic healthy subjects were enrolled. We performed shotgun proteomic analysis to investigate the proteome of ultracentrifugally isolated HDL. We identified 79 HDL-associated proteins involved in lipid metabolism, protease inhibition, complement regulation, and acute-phase response, including 5 potential newly identified HDL-associated proteins such as angiopoietin-like3 (ANGPTL3). Spectral counts of apolipoprotein (apo) E were increased in patients with CETP-D compared with controls (60.3 ± 6.9 vs 43.7 ± 2.5, P < .001), which is concordant with our previous report. Complement regulatory proteins such as C3, C4a, C4b, and C9 were also significantly enriched in HDL from patients with CETP-D. Furthermore, apoC-III and ANGPTL3, both of which are now known to associate with increased atherosclerotic cardiovascular diseases, were enriched in patients with CETP-D compared with normolipidemic subjects (35.9 ± 5.3 vs 27.1 ± 3.7, 2.3 ± 1.1 vs 0.4 ± 1.1, respectively; P < .01). We have characterized HDL-associated proteins in patients with CETP-D. We identified a significant increase in the amount of apoE, apoC-III, ANGPTL3, and complement regulatory proteins. These proteomic changes might be partly responsible for the enhanced atherogenicity of patients with CETP-D. Show less

Fasting and postprandial hypertriglyceridemia (PHTG) are caused by the accumulation of triglyceride (TG)-rich lipoproteins and their remnants, which have atherogenic effects. Fibrates can improve fasting and PHTG; however, reduction of remnants is clinically needed to improve health outcomes. In the current study, we investigated the effects of a novel selective peroxisome proliferator-activated receptor α modulator (SPPARMα), K-877 (Pemafibrate), on PHTG and remnant metabolism. Male C57BL/6J mice were fed a high-fat diet (HFD) only, or an HFD containing 0.0005% K-877 or 0.05% fenofibrate, from 8 to 12 weeks of age. After 4 weeks of feeding, we measured plasma levels of TG, free fatty acids (FFA), total cholesterol (TC), HDL-C, and apolipoprotein (apo) B-48/B-100 during fasting and after oral fat loading (OFL). Plasma lipoprotein profiles after OFL, which were assessed by high performance liquid chromatography (HPLC), and fasting lipoprotein lipase (LPL) activity were compared among the groups. Both K-877 and fenofibrate suppressed body weight gain and fasting and postprandial TG levels and enhanced LPL activity in mice fed an HFD. As determined by HPLC, K-877 and fenofibrate significantly decreased the abundance of TG-rich lipoproteins, including remnants, in postprandial plasma. Both K-877 and fenofibrate decreased intestinal mRNA expression of ApoB and Npc1l1; however, hepatic expression of Srebp1c and Mttp was increased by fenofibrate but not by K-877.Hepatic mRNA expression of apoC-3 was decreased by K-877 but not by fenofibrate. K-877 may attenuate PHTG by suppressing the postprandial increase of chylomicrons and the accumulation of chylomicron remnants more effectively than fenofibrate. Show less

We previously reported that patients with cholesteryl ester transfer protein (CETP) deficiency (CETP-D) have a higher prevalence of atherosclerotic cardiovascular disease, in spite of increased HDL-C levels. However, characterization of HDL in CETP-D has not been well described. Therefore, we examined HDL particle number (PN) rather than HDL-C level. Nine patients with CETP-D and 9 normolipidemic subjects were enrolled. We performed gel permeation high-performance liquid chromatography (GP-HPLC) analysis, determined the cholesterol and triglyceride composition of all lipoprotein subclasses, and calculated the PN of each subclass, which consisted of 3 VLDL (large, medium, and small), 4 LDL (large, medium, small, and very small), and 5 HDL (very large, large, medium, small, and very small) subclasses. The PNs of large and medium LDL were significantly lower in CETP-D than that in healthy subjects (0.66- and 0.63-fold decrease, respectively; p<0.001), whereas the PN of very small LDL, which is known to be atherogenic, was significantly higher (1.36-fold increase, p = 0.016). The PNs of very large and large HDL in CETP-D were markedly higher than that in healthy subjects (19.9- and 4.5-fold increase, respectively; p<0.001), whereas the PNs of small and very small HDL, which have more potent anti-atherogenic functions, were significantly lower (0.76- and 0.61-fold decrease, respectively; p<0.001). We have assessed the PNs of detailed subclasses of patients with CETP-D for the first time. The PN of larger HDL was markedly increased, that of smaller HDL was decreased, and that of very small LDL was increased, suggesting that CETP-D has pro-atherogenic lipoprotein properties. Show less

Protein phosphatase 6 (PP6) is an essential Ser/Thr phosphatase conserved among eukaryotes. The Saccharomyces cerevisiae homologue of PP6 called Sit4 depends on association with SAPS domain subunits. This study used a human SAPS domain subunit FLAG-PP6R1 to identify endogenous interacting proteins. Mass spectrometry identified coprecipitating proteins as PP6 catalytic subunit and three ankyrin repeat proteins (Ankrd28, Ankrd44, and Ankrd52). These proteins have extensive sequence identity to one another but segregate into separate branches on a phylogenetic tree for vertebrate species, suggesting individual biological functions. Tagged Ankrd28 coprecipitated with PP6, not with PP2A or PP4, and with SAPS domain subunits PP6R1 and PP6R3. Tagged PP6 coprecipitated endogenous SAPS domain subunits and Ankrd28. The C-terminal region of PP6R1 was sufficient to coprecipitate Ankrd28, but not PP6, demonstrating that PP6R1 acts as a scaffold with separate regions for binding to PP6 and to Ankrd28. Endogenous PP6 holoenzymes with PP6R1 and PP6R3 subunits were resolved by DEAE chromatography and eluted together with Ankrd28 at Mr > 440 kDa from Superose 12. Knockdown of PP6R1 or Ankrd28, but not PP6R3, produced equivalent enhancement of IkappaBepsilon degradation in response to TNFalpha. The results suggest that PP6 functions as a heterotrimer, composed of the PP6 catalytic subunit bound to a SAPS domain scaffold subunit that associates with Ankrd28. We propose that the SAPS and ankyrin repeat regulatory subunits determine the function and specificity of PP6. Show less

Plasma high density lipoprotein (HDL)-cholesterol levels are inversely correlated to the risk of atherosclerotic cardiovascular diseases. Reverse cholesterol transport (RCT) is one of the major protective systems against atherosclerosis, in which HDL particles play a crucial role to carry cholesterol derived from peripheral tissues to the liver. Recently, ATP-binding cassette transporters (ABCA1, ABCG1) and scavenger receptor (SR-BI) have been identified as important membrane receptors to generate HDL by removing cholesterol from foam cells. Adiponectin (APN) secreted from adipocytes is one of the important molecules to inhibit the development of atherosclerosis. Epidemiological studies have revealed a positive correlation between plasma HDL-cholesterol and APN concentrations in humans, although its mechanism has not been clarified. Therefore, in the present study, we investigated the role of APN on RCT, in particular, cellular cholesterol efflux from human monocyte-derived and APN-knockout (APN-KO) mice macrophages. APN up-regulated the expression of ABCA1 in human macrophages, respectively. ApoA-1-mediated cholesterol efflux from macrophages was also increased by APN treatment. Furthermore, the mRNA expression of LXRalpha and PPARgamma was increased by APN. In APN-KO mice, the expression of ABCA1, LXRalpha, PPARgamma, and apoA-I-mediated cholesterol efflux was decreased compared with wild-type mice. In summary, APN might protect against atherosclerosis by increasing apoA-I-mediated cholesterol efflux from macrophages through ABCA1-dependent pathway by the activation of LXRalpha and PPARgamma. Show less