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Objectives: Diabetes secondary to chronic pancreatitis (CP) presents clinical challenges due to lack of understanding on factor(s) triggering insulin secretory defects. Therefore, we aimed to delineate the molecular mechanism of β-cell dysfunction in CP., Materials and Methods: Transcriptomic analysis was conducted to identify endocrine-specific receptor expression in mice and human CP on microarray. The identified receptor (NR4A1) was overexpressed in MIN6 cells using PEI linear transfection. RNA-Seq analysis of NR4A1-overexpressed (OE) MIN6 cells on NovaSeq6000 identified aberrant metabolic pathways. Upstream trigger for NR4A1OE was studied by InBio Discover and cytokine exposure, whereas downstream effect was examined by Fura2 AM-based fluorimetric and imaging studies. Mice with CP were treated with IFN-γ-neutralizing monoclonal antibodies to assess NR4A1 expression and insulin secretion., Results: Increased expression of NR4A1 associated with decreased insulin secretion in islets (humans: controls 9 ± 0.2, CP 3.7 ± 0.2, mice: controls 8.5 ± 0.2, CP 2.1 ± 0.1 μg/L). NR4A1OE in MIN6 cells (13.2 ± 0.1) showed reduction in insulin secretion (13 ± 5 to 0.2 ± 0.1 μg/mg protein per minute, P = 0.001) and downregulation of calcium and cAMP signaling pathways. IFN-γ was identified as upstream signal for NR4A1OE in MIN6. Mice treated with IFN-γ-neutralizing antibodies showed decreased NR4A1 expression 3.4 ± 0.11-fold ( P = 0.03), showed improved insulin secretion (4.4 ± 0.2-fold, P = 0.01), and associated with increased Ca 2+ levels (2.39 ± 0.06-fold, P = 0.009)., Conclusions: Modulating NR4A1 expression can be a promising therapeutic strategy to improve insulin secretion in CP., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)

We have previously reported that bacterial endotoxin LPS attenuates expression of PHLPP, a ser/thr phosphatase, at both transcript and protein levels in different immune cells, however the underlying molecular mechanism is unknown and is of significant interest. Here, in line with the decreased transcript levels upon LPS treatment, we observed that LPS caused significant reduction in PHLPP promoter activity. We observed that SP1, a transcription factor frequently associated with inflammation, was recruited to the PHLPP promoter region. Ectopic expression of SP1 enhanced both transcript and protein levels of PHLPP while knockdown of SP1 or pharmacological inhibition of SP1 DNA binding by mithramycin reduced PHLPP expression. Moreover, over-expression of SP1 co-activators CBP/p300 augmented SP1 driven PHLPP promoter activity. Of note, LPS treatment depleted SP1 and CBP protein levels due to which recruitment of SP1 to PHLPP promoter was reduced. Further, we found that re-introduction of SP1 restored promoter activity and transcript levels of PHLPP in LPS stimulated cells. Collectively, our data revealed the molecular mechanism underlying the regulation of PHLPP expression during LPS induced macrophage inflammatory response., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Chronic inflammatory diseases such as insulin resistance, Type 2 diabetes, neurodegenerative diseases etc., are shown to be caused due to imbalanced activation states of macrophages. MicroRNAs which are transcriptional/post-transcriptional regulators of gene expression drive several pathophysiological processes including macrophage polarization. However the functional role of microRNAs in regulating inflammation induced insulin resistance is ill defined. In our current study we observed that the expression of miR-712 was reduced in macrophages exposed to LPS and IFN-γ. Ectopic expression of miR-712 in RAW 264.7 mouse macrophages impaired the expression of iNOS protein and secretion of pro-inflammatory cytokines such as TNF-α, IL-6 and IFN-β which in turn led to improved insulin stimulated glucose uptake in co-cultured L6 myoblasts. Mechanistically, we identified that miR-712 targets the 3'UTR of a potent inflammatory gene LRRK2 and dampens the phosphorylation of p38 and ERK1/2 kinases. Taken together, our data underscore the regulatory role of miR-712 in restoring insulin stimulated glucose uptake by myoblasts through down-regulating macrophage mediated inflammatory responses., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Uncontrolled inflammation leads to several diseases such as insulin resistance, T2D and several types of cancers. The functional role of microRNAs in inflammation induced insulin resistance is poorly studied. MicroRNAs are post-transcriptional regulatory molecules which mediate diverse biological processes. We here show that miR-16 expression levels are down-regulated in different inflammatory conditions such as LPS/IFNγ or palmitate treated macrophages, palmitate exposed myoblasts and insulin responsive tissues of high sucrose diet induced insulin resistant rats. Importantly, forced expression of miR-16 in macrophages impaired the production of TNF-α, IL-6 and IFN-β leading to enhanced insulin stimulated glucose uptake in co-cultured skeletal myoblasts. Further, ectopic expression of miR-16 enhanced insulin stimulated glucose uptake in skeletal myoblasts via the up-regulation of GLUT4 and MEF2A, two key players involved in insulin stimulated glucose uptake. Collectively, our data highlight the important role of miR-16 in ameliorating inflammation induced insulin resistance., (Copyright © 2015 Elsevier B.V. and Société Française de Biochimie et Biologie Moléculaire (SFBBM). All rights reserved.)

The mechanisms underlying inflammation induced insulin resistance are poorly understood. Here, we report that the expression of PIMT, a transcriptional co-activator binding protein, was up-regulated in the soleus muscle of high sucrose diet (HSD) induced insulin resistant rats and TNF-α exposed cultured myoblasts. Moreover, TNF-α induced phosphorylation of PIMT at the ERK1/2 target site Ser(298). Wild type (WT) PIMT or phospho-mimic Ser298Asp mutant but not phospho-deficient Ser298Ala PIMT mutant abrogated insulin stimulated glucose uptake by L6 myotubes and neonatal rat skeletal myoblasts. Whereas, PIMT knock down relieved TNF-α inhibited insulin signaling. Mechanistic analysis revealed that PIMT differentially regulated the expression of GLUT4, MEF2A, PGC-1α and HDAC5 in cultured cells and skeletal muscle of Wistar rats. Further characterization showed that PIMT was recruited to GLUT4, MEF2A and HDAC5 promoters and overexpression of PIMT abolished the activity of WT but not MEF2A binding defective mutant GLUT4 promoter. Collectively, we conclude that PIMT mediates TNF-α induced insulin resistance at the skeletal muscle via the transcriptional modulation of GLUT4, MEF2A, PGC-1α and HDAC5 genes.