Saturated fatty acids entrap PDX1 in stress granules and impede islet beta cell function

Abstract

Aims/hypothesis

Failure of pancreatic and duodenal homeobox factor 1 (PDX1) to localise in the nucleus of islet beta cells under high-fat diet (HFD) conditions may be an early functional defect that contributes to beta cell failure in type 2 diabetes; however, the mechanism of PDX1 intracellular mislocalisation is unclear. Stress granules (SGs) are membrane-less cytoplasmic structures formed under stress that impair nucleocytoplasmic transport by sequestering nucleocytoplasmic transport factors and components of the nuclear pore complex. In this study, we investigated the stimulators that trigger SG formation in islet beta cells and the effects of SGs on PDX1 localisation and beta cell function.

Methods

The effect of palmitic acid (PA) on nucleocytoplasmic transport was investigated by using two reporters, S-tdTomato and S-GFP. SG assembly in rat insulinoma cell line INS1 cells, human islets under PA stress, and the pancreas of diet-induced obese mice was analysed using immunofluorescence and immunoblotting. SG protein components were identified through mass spectrometry. SG formation was blocked by specific inhibitors or genetic deletion of essential SG proteins, and then PDX1 localisation and beta cell function were investigated in vitro and in vivo.

Results

We showed that saturated fatty acids (SFAs) are endogenous stressors that disrupted nucleocytoplasmic transport and stimulated SG formation in pancreatic beta cells. Using mass spectrometry approaches, we revealed that several nucleocytoplasmic transport factors and PDX1 were localised to SGs after SFA treatment, which inhibited glucose-induced insulin secretion. Furthermore, we found that SFAs induced SG formation in a phosphoinositide 3-kinase (PI3K)/eukaryotic translation initiation factor 2α (EIF2α) dependent manner. Disruption of SG assembly by PI3K/EIF2α inhibitors or genetic deletion of T cell restricted intracellular antigen 1 (TIA1) in pancreatic beta cells effectively suppressed PA-induced PDX1 mislocalisation and ameliorated HFD-mediated beta cell dysfunction.

Conclusions/interpretation

Our findings suggest a link between SG formation and beta cell dysfunction in the presence of SFAs. Preventing SG formation may be a potential therapeutic strategy for treating obesity and type 2 diabetes.

Graphical abstract

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Data availability

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

Abbreviations

ALS:

Amyotrophic lateral sclerosis

EIF2α:

Eukaryotic translation initiation factor 2α

ER:

Endoplasmic reticulum

G3BP1:

GAP SH3 binding protein 1

GSIS:

Glucose-stimulated insulin secretion

HFD:

High-fat diet

ISRIB:

Integrated stress response inhibitor

NES:

Nuclear export sequence

NLS:

Nuclear localisation signal

PA:

Palmitic acid

PDX1:

Pancreatic and duodenal homeobox factor 1

PI3K:

Phosphoinositide 3-kinase

PIC:

Stalled (preinitiation) translation complex

RAN:

Ran GTPase

SFA:

Saturated fatty acid

SG:

Stress granule

siRNA:

Small interfering RNA

TIA1:

T cell restricted intracellular antigen 1

TIAL1:

TIA1 cytotoxic granule associated RNA binding protein like 1

WCL:

Whole cell lysate

WT:

Wild-type

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Acknowledgements

The S-GFP plasmid was a kind gift from F. U. Hartl (Department of Cellular Biochemistry, the Max Planck Institute of Biochemistry, Germany). We thank W. Liu (Institute of Translational Medicine, Nanjing Medical University, China) for valuable suggestions. We thank J. Zhang (The Second Xiangya Hospital of Central South University, China) for technical support with INS1 cell culture.

Authors’ relationships and activities

The authors declare that there are no relationships or activities that might bias, or be perceived to bias, their work.

Funding

This work was supported by the National Key R&D Program of China (grant no. 2016YFC1305000), the National Natural Science Foundation of China (grant no. 81803750, 81770778), the Key Medical Talents Project of Jiangsu Province (grant no. ZDRCA2016088), the Key Project of Jiangsu Science and Technology Plan (grant no. BE2017738) and the Jiangsu Province Innovative and Entrepreneurial Team Grant. This project was also supported by the Project Program of State Key Laboratory of Natural Medicines, China Pharmaceutical University (SKLNMZZCX201820) and the “Double First-Class” University Project (CPU2018GF04).

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YuL, CQ and MuZ conceived and designed the work. MuZ, CQ and CJY performed the cell experiments and acquired data. XJX and HMC performed the animal experiments and acquired data. MengZ, LQ, YanL and RG contributed to sample preparation and data acquisition. MuZ and CQ interpreted the data and wrote the manuscript. CJY, XJX, HMC, MengZ, LQ, YanL and RG made contributions to revising the article for important intellectual content. YuL revised the manuscript critically. All authors gave final approval of the version to be published. YuL is the guarantor of this work, has full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

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Correspondence to Xiaojun Xu or Cheng Qian or Yu Liu.

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Zhang, M., Yang, C., Zhu, M. et al. Saturated fatty acids entrap PDX1 in stress granules and impede islet beta cell function. Diabetologia (2021). https://doi.org/10.1007/s00125-021-05389-4

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Keywords

  • Glucose-stimulated insulin secretion
  • Pancreatic and duodenal homeobox factor 1
  • Saturated fatty acids
  • Stress granules
  • Type 2 diabetes