Dissertation defence (Cell Biology and Anatomy): MSc Nicko Widjaja
MSc Nicko Widjaja defends the dissertation in Cell Biology and Anatomy titled “Bone Marrow Adipose Tissue: A Distinct and Metabolically Active Fat Depot” at the University of Turku on 27 November 2026 at 12.00 (University of Turku, Medisiina C, Osmo Järvi lecture hall, Kiinamyllynkatu 10, Turku).
Opponent: Professor Christa Maes (Katholieke Universiteit Leuven, Belgium)
Custos: Adjunct Professor Kaisa Ivaska (University of Turku)
Summary of the Doctoral Dissertation:
Adipose tissue, commonly known as fat, is a specialised organ that helps regulate energy balance by storing excess nutrients and releasing those when energy is needed, such as during exercise or fasting. Fat is distributed throughout the body in distinct depots, each with its own characteristics and functions. Subcutaneous fat, found beneath the skin, stores excess dietary energy, whereas brown fat, found in certain specific areas, generates heat in response to cold. Interestingly, fat is also found inside our bones, within the bone marrow. However, our understanding of this bone marrow fat remains limited, particularly regarding how it differs from other fat depots and what role it plays in the body's metabolism.
This doctoral dissertation explores the characteristics and metabolic functions of bone marrow fat in laboratory rats. First, we investigated how adipocytes – the principal nutrient-handling cells of adipose tissue – respond to a high-fat diet. We found that bone marrow adipocytes became significantly larger after the dietary intervention, signifying their metabolic activity in response to the changes in dietary fat intake. We then examined whether dietary changes and running exercise could reverse these effects. Despite a significant reduction in the overall body fat percentage, the size of bone marrow adipocytes remained largely unchanged. These findings suggest that bone marrow fat behaves differently than the other fat depots.
To explore these differences further, we analysed samples of adipose tissues at the molecular level using a scientific technology called RNA-sequencing. This enabled us to obtain a comprehensive overview – known as a transcriptome – of each fat depot, as if we saw the whole forest for the trees. The transcriptomes of each adipose tissue (the forest in the previous analogy) contain distinct patterns of RNA expression (individual trees), supporting the evidence that bone marrow fat is distinct from white and brown fats at the molecular level. We also observed that several biological pathways related to lipid uptake were activated in rats fed with a high-fat diet. This previously less-known mechanism of lipid uptake provides the molecular evidence for the metabolic role of bone marrow adipocytes.
The metabolic activity of cells and the rate at which glucose is taken up by adipocytes can be measured by tracing a radioactive glucose analogue. Using this method, we found that the bone marrow, which is enriched in adipocytes, had higher levels of glucose uptake than the skeletal muscle and liver. This result provides further evidence that bone marrow fat is metabolically active and participates in the body's handling of nutrients.
In summary, my doctoral research studies the previously rather unknown fat depot located inside bone marrow at the cellular (adipocyte size) and molecular (RNA-sequencing and glucose uptake measurement) levels. Moreover, moderate dietary changes and running exercise were insufficient to significantly alter bone marrow adipocyte size after a period of high-fat feeding. These findings highlight the distinctive biology of bone marrow fat and provide the groundwork to further understand its contribution to health and disease. Overall, this doctoral dissertation compiles two novel findings about bone marrow adipose tissue and highlights its role as a distinct and metabolically active fat depot.
