Ivanovic 2022 Abstract Bioblast

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P13.
Ivanovic Tijana
Ivanovic Tijana, Krako Jakovljevic N, Pavlovic K, Ciric D, Kravic-Stevovic T, Markovic I, Lalic NM (2022) Relationship of insulin resistance and mitochondria-associated endoplasmic reticulum membranes MAM in an in vitro lipotoxicity model.
Bioblast 2022: BEC Inaugural Conference. In: https://doi.org/10.26124/bec:2022-0001

Link: Bioblast 2022: BEC Inaugural Conference

Ivanovic Tijana, Krako Jakovljevic Nina, Pavlovic Kasja, Ciric D, Kravic-Stevovic T, Markovic Ivanka, Lalic Nebojsa M (2022)

Event: Bioblast 2022

Excessive lipid accumulation in hepatic cells is the hallmark of several metabolic disorders, particularly hepatic steatosis, insulin resistance (IR) and diabetes mellitus. Recent studies have shown that phosphorylation of Akt, a key kinase in the insulin signaling pathway, may occur in ER – mitochondria contact sites, known as MAMs (Mitochondria-Associated endoplasmic reticulum Membranes) [1]. One of the key MAM proteins is Glucose–regulated protein 75 (Grp75) which enables calcium transport from endoplasmic reticulum to mitochondria. Grp75 levels were found to be significantly reduced in IR in vitro, along with Akt phosphorylation levels and MAM concentration, implying that this protein could be the link between IR and MAM. Furthermore, mitochondrial dysfunction has widely been associated with diabetes and IR, which highlights the importance of MAM exploration. In order to investigate the effects of lipotoxicity on MAM and mitochondrial function, we treated hepatocytes with palmitate, a common unsaturated fatty acid used for studying in vitro lipotoxicity.

Human hepatocellular carcinoma (Huh7) cell line was used for all experiments. Cells were treated with 0.4 mM palmitate for 24 h. Cell viability was estimated by using acid phosphatase assay. For microscopy analysis, cells were transfected with Split - GFP pasmid that targets MAM region, and stained with MitoTracker Red. Samples were examined using confocal microscopy. For investigating insulin signalling and MAM protein levels, immunoblotting was performed. Mitochondrial respiration was measured with Oroboros O2k high-resolution respirometry.

Viability of Huh7 cells was not affected by palmitate. Preliminary data showed that palmitate treated cells had a lower number of MAM and lower mitochondrial content with reduced levels of GRP75, compared to untreated cells. Palmitate treatment impaired insulin response, observed as lower phosphorylated Akt levels compared to untreated cells. Mitochondrial function was altered in PA treated cells, which was observed by lower respiration rate in ROUTINE and OXPHOS state and P-L control efficiency (1-L/P) compared to control cells, as characterized previously in detail [1].

To conclude, palmitate treatment induced IR, which was confirmed by impaired insulin signaling. Furthermore, the adverse effects were found in mitochondrial function and content and number of MAM, which may imply the potential of MAM in insulin signaling. Taking into account that mitochondria in our model had decreased respiration rate and impaired coupling efficiency, it is important to additionally clarify the relationship between these processes and their importance for mitochondrial function and energy metabolism.

  1. Krako Jakovljevic N et al (2021) In vitro models of insulin resistance: Mitochondrial coupling is differently affected in liver and muscle cells. https://doi.org/10.1016/j.mito.2021.10.001

Keywords: lipotoxicity, diabetes, hepatocytes, MAM, mitochondria

O2k-Network Lab: RS Belgrade Lalic NM


Affiliations

Ivanovic T1, Krako Jakovljevic N1, Pavlovic K1, Ciric D2, Kravic-Stevovic T2, Markovic I3, Lalic NM1
  1. Clinic for Endocrinology, Diabetes and Metabolic Diseases, Clinical Centre of Serbia, Faculty of Medicine, Univ Belgrade - [email protected]
  2. Inst of Histology and Embryology, Faculty of Medicine, Univ Belgrade
  3. Inst of Medical and Clinical Biochemistry, Faculty of Medicine, Univ Belgrade

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