Download 2016 department of medicine research day

2016 DEPARTMENT OF MEDICINE RESEARCH DAY
Title of Poster: Cytokines provoke G1 arrest and mitochondrial network dysfunction in
beta-cells
Presenter: Dr Chiara Montemurro
Division: Endocrinology/Medicine
☐ Faculty ☐ Fellow ☐ Resident ☒ Post-doc Research Fellow ☐ Graduate Student ☐ Medical Student ☐Other
Principal Investigator/Mentor: Dr Slavica Tudzarova-Trajkovska
Butler, Kenny Ekachai Vongbunyong and Peter Cawood Butler
Thematic Poster Category:
Co-Investigators: Tatyana Gurlo, Alexandra E
Nutrition, Digestion and Metabolism
Abstract
Background: Despite a greater capacity for beta-cell replication, the rate of beta-cell loss and diabetes
onset in individuals who develop type 1 diabetes is more rapid in young childhood than in adults. The
reduction of beta-cell mass is believed to be due to beta cell apoptosis mediated by the release of
cytokines, such as IL-1β, TNF-α and IFN-γ, known to induce cell death via induction of mitochondrial
stress. We questioned whether cytokines could block the progression of beta cells through the cell
cycle, increasing their vulnerability to cell death, along with mitochondrial network dysfunction.
Study design: To test this hypothesis, we evaluated DNA content profile, mitochondrial network and
apoptosis in cells synchronized at different stages of cell cycle prior exposure to cytokines or vehicle.
Cells were synchronized at G1/S, S and G2/M by serum starvation and aphidicolin addiction.
Enrichment of cells in different phases of cell cycle was demonstrated by FACS analysis of DNA
content.
Results: Beta-cells at G1/S transition showed a highly interconnected tubular filamentous
mitochondrial network that underwent fragmentation in S and G2/M phases. Fragmentation of
mitochondria advancing through cell cycle was associated with increased expression of the
mitochondrial fission protein pDRP1. Mitochondrial respiration and glycolysis were both increased in S
and G2/M phases compared to G1/S. Cytokine treatment caused a marked increase in apoptosis in
cells synchronized at G1/S phase. The proportion of beta-cells that transitioned to the S phase was
only ~30% of controls after prior exposure to cytokines with a similar proportion reaching the G2/M
phase of cell cycle check point. Cells in G1/S exposed to cytokines had fragmented and swollen
mitochondria; this effect of cytokines on mitochondrial morphology was not readily appreciable in beta
cells at the S and G2/M phases of cell cycle. Reduction of mitochondrial function and glycolysis caused
by cytokines in cells at G1/S was persistent in cells that transitioned in S and G2/M phases.
Conclusion: Shape and function of the mitochondrial network adaptively undergo transition during
beta-cell cycle. Cytokines cause cell cycle arrest and death at the G1/S check point together with
mitochondrial dysfunction. These data are consistent with the hypothesis that loss of beta cell mass in
type 1 diabetes may be accelerated in young children due to increased vulnerability of beta cells
entering cell cycle. In this perspective, therapies stimulating beta-cell division in patients with type 1
diabetes should be carefully evaluated.