Mitochondria-related transcriptional signature is downregulated in adipocytes in obesity ‒ a study of young healthy MZ twins

Supplementary data tables

Mitochondria-related transcriptional signature is downregulated in adipocytes in obesity ‒ a study of young
healthy MZ twins

Sini
Heinonen 1, Maheswary Muniandy1, Jana Buzkova2,
Adil Mardinoglu3,4, Amaia Rodríguez5, Gema Frühbeck5,
Antti Hakkarainen6, Jesper Lundbom6,7, Nina Lundbom6,
Jaakko Kaprio8,9,10, Aila Rissanen1,11, Kirsi
H. Pietiläinen1,8,12

1Obesity Research Unit,
Research Programs Unit, Diabetes and Obesity, University of Helsinki, Helsinki,
Finland 00014, 2Research Programs Unit, Molecular Neurology,
Biomedicum-Helsinki, University of Helsinki, Helsinki, Finland 00290, 3Department of Biology and Biological Engineering,
Chalmers University of Technology, SE‑412 96, Gothenburg, Sweden, 4Science for
Life Laboratory, KTH - Royal Institute of Technology, SE‑171 21, Stockholm, Sweden 5Metabolic Research Laboratory, Clínica
Universidad de Navarra, &

 CIBERobn, Instituto de Salud Carlos III,
Pamplona, Spain 31008, 6HUS Medical Imaging Center, Radiology,
University of Helsinki and Helsinki University Hospital, Helsinki, Finland 00014, 7Institute
for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes
Research, Heinrich Heine University, Düsseldorf, Germany, 8FIMM,
Institute for Molecular Medicine, University of Helsinki, Helsinki, Finland
00014,  9Finnish
Twin Cohort Study, Department of Public Health, University of Helsinki,
Helsinki Finland 00014, 10National Institute for Health and Welfare,
Department of Health, Helsinki, Finland 00271, 11Department of
Psychiatry, Helsinki University Central Hospital, Helsinki, Finland,12Endocrinology,
Abdominal Center, Helsinki University Hospital and University of Helsinki,
Helsinki, Finland 00290.

Abstract

Introduction:

Low mitochondrial activity in adipose tissue is
suggested to be an underlying factor in obesity and its metabolic
complications. It is still unknown however whether this is due to malfunction
of adipocytes or of other cells in adipose tissue.

Methods:

We studied young adult monozygotic (MZ) twin pairs
discordant (n = 14, intrapair
difference ΔBMI > 3 kg/m2) and concordant (n = 5, ΔBMI < 3 kg/m2) for BMI, identified from ten
birth cohorts of 22-36-year-old Finnish twins. Abdominal body fat distribution (magnetic
resonance imaging, MR), liver fat content (MR spectroscopy), insulin
sensitivity (oral glucose tolerance test OGTT), hs-CRP, serum lipids and
adipokines were measured. Subcutaneous abdominal adipose tissue biopsies were
obtained to analyze the transcriptomics patterns (Affymetrix U133 Plus 2.0
chips) of the
isolated adipocytes, as well as of the whole adipose tissue. Mitochondrial DNA
(mtDNA) transcript levels in adipocytes were measured by qRT-PCR. Western blots
of oxidative phosphorylation (OXPHOS) protein levels in adipocytes were
performed in heavy and lean unrelated individuals.

Results:

The heavier (BMI 29.9 ± 1.0 kg/m2) co-twins
of the discordant twin pairs had more subcutaneous, intra-abdominal and liver
fat and were more insulin-resistant (p<0.01
for all measures) than the leaner (24.1 ± 0.9 kg/m2) co-twins. Altogether
2538 genes in adipocytes and 2135 in adipose tissue were significantly
differentially expressed (nominal p<0.05)
between the co-twins. Pathway-analysis of these transcripts in both isolated
adipocytes and adipose tissue revealed that the heavier co-twins had reduced expression
of mitochondrial pathways, a result that was replicated when analyzing the
pathways behind most consistently downregulated genes in the heavy co-twins (in
at least 12 out of 14 pairs). Consistently upregulated genes in adipocytes were
related to inflammation.

As previously found in adipose tissue, we now
confirmed that mitochondrial DNA transcript levels (12S RNA, 16S RNA, COX1, ND5, CYTB; qRT-PCR),
expression of mitochondrial ribosomal protein transcripts (Affymetrix) and a
major mitochondrial regulator PGC-1α were reduced in the heavier co-twins’
adipocytes (p<0.05). OXPHOS
protein levels of complex I and III in adipocytes were lower in heavier than in
leaner individuals.

Conclusion:

Subcutaneous abdominal
adipocytes in obesity show global expressional downregulation of oxidative
pathways, mitochondrial transcripts and OXPHOS protein levels, and upregulation
of inflammatory pathways.

1. Conflict of Interest: None 

2. Funding:  Orion Foundation,
Biomedicum Helsinki Foundation, Paulo Foundation, Finnish Medical Foundation,
Maud Kuistila Foundation, Emil Aaltonen Foundation, Academy of Finland (Center
of Excellence grant# 265240, 272376, 263278
and 266286), Novo Nordisk
Foundation, Jalmari and Rauha Ahokas Foundation, Finnish Diabetes Research Foundation,
Finnish Foundation for Cardiovascular Research, Knut and Alice Wallenberg
Foundation, Fondo de Investigación Sanitaria-FEDER and CIBEROBN from the
Instituto de  Salud Carlos III, Spain, University
of Helsinki and Helsinki University Central Hospital grants.

Keywords:

Adipocytes, gene expression, mitochondria, obesity, twins