The Identification of Potential Factors Associated with the Development of Type 2 Diabetes

Abstract

Type 2 diabetes (T2D) arises when pancreatic ␤-cells fail to compensate for systemic insulin resistance with appropriate insulin secretion. However, the link between insulin resistance and ␤-cell failure in T2D is not fully understood. To explore this association, we studied transgenic MKR mice that initially develop insulin resistance in skeletal muscle but by 8 weeks of age have T2D. In the present study, global islet protein and gene expression changes were characterized in diabetic MKR versus non-diabetic control mice at 10 weeks of age. Using a quantitative proteomics approach (isobaric tags for relative and absolute quantification (iTRAQ)), 159 proteins were differentially expressed in MKR compared with control islets. Marked up-regulation of protein biosynthesis and endoplasmic reticulum stress pathways and parallel down-regulation in insulin processing/secretion, energy utilization, and metabolism were observed. A fraction of the differentially expressed proteins identified (including GLUT2, DNAJC3, VAMP2, RAB3A, and PC1/3) were linked previously to insulin-secretory defects and T2D. However, many proteins for the first time were associated with islet dysfunction, including the unfolded protein response proteins (ERP72, ERP44, ERP29, PPIB, FKBP2, FKBP11, and DNAJB11), endoplasmic reticulumassociated degradation proteins (VCP and UFM1), and multiple proteins associated with mitochondrial energy metabolism (NDUFA9, UQCRH, COX2, COX4I1, COX5A, ATP6V1B2, ATP6V1H, ANT1, ANT2, ETFA, and ETFB). The mRNA expression level corresponding to these proteins was examined by microarray, and then a small subset was validated using quantitative real time PCR and Western blot analyses. Importantly ϳ54% of differentially expressed proteins in MKR islets (including proteins involved in proinsulin processing, protein biosynthesis, and mitochondrial oxidation) showed changes in the proteome but not transcriptome, suggesting post-transcriptional regulation. These results underscore the importance of integrated mRNA and protein expression measurements and validate the use of the iTRAQ method combined with microarray to assess global protein and gene changes involved in the development of T2D.

UFM1 Protects Macrophages from oxLDL-Induced Foam Cell Formation Through a Liver X Receptor α Dependent Pathway

“…On the contrary, the efflux of accumulated cholesterol in macrophages is mediated by the cholesterol reverse transporter family, including SR-BI, ABCA1, and ABCG1 41,42) . Therefore, we delineated the mechanism of UFM1 to attenuate lipid accumulation by examining the alterations results are consistent with a previous report that UFM1 is expressed in various tissues and cell lines and that UFM1 is linked with the acti vation of the ER stress response in atherosclerosis, ischemic heart injury, and T2D 21,48,49) . Taken together, our findings strongly indicate that UFM1 is upregulated in ma crophages under atherosclerotic conditions, both in vivo and in vitro and that UFM1 may be a potential therapeutic target for atherosclerosis.…”

Supplement of TCA cycle intermediates protects against high glucose/palmitate-induced INS-1 beta cell death

“…Reports showing that the flux of the TCA cycle was reduced in type 2 diabetes and that an enhanced mitochondrial metabolism accounted for adaptation of beta cells to high-fat diet-induced insulin resistance [40,41] support that appropriate oxidation metabolism is essential for maintenance of cell viability in HG/PA-exposed beta cells. In addition to an insufficient supply of fuel substrates, it was reported that the ATP synthesis process was impaired in FFA-treated cells [42,43] and expression of the molecules related to energy metabolism were decreased in islets of diabetic subjects [44]. Collectively, energy-producing metabolism is impaired in HG/PA-treated cells, which may explain the induction of beta cell glucolipotoxicity.…”

Proteomics in diabetes research

“…A β-cell hypertrophy is also seen in the MKR mouse, an insulin resistance model (Lu, et al 2008). The MKR mouse harbours a dominant-negative insulin-like growth factor-1 receptor mutation specifically targeted to skeletal muscle (Fernandez, et al 2001), thus they have no primary β-cell defect.…”