JOIN USScientists are trying to demystify the biology of glioblastoma, a type of brain tumour, which is considered more dangerous than the other types, writes Bharani Muppavarapu
The story of glioblastoma research has all the makings of a Dan Brown novel; the protagonist making small but sure steps towards understanding his rival’s malicious intentions and the unravelling of a plot that seems to thicken with every page. The ‘rival’ in my metaphor is glioblastoma, a highly aggressive and a grievously common form of brain tumour that occurs in adults. It is known for being notoriously unresectable due to its high metastasing capacity, which may sometimes involve important regions of the brain. The ‘Robert Langdons’ (the protagonist of Dan Brown’s Robert Langdon series) of this story are the scientists attempting to unravel the biology of glioblastoma, in an attempt to identify where the deregulation occurs; in other words, the scene of the crime.
Researchers in the laboratory of Professor Kumaravel Somasundaram at the Department of Microbiology and Cell Biology at the Indian Institute of Science (IISc), Bengaluru have progressed closer to demystifying the biology of glioblastoma with their recent work. “We have identified epigenetically regulated fibromodulin as an inducer of glioma cell migration and it might serve as a potential target for developing therapeutic strategies in glioblastoma,” says Baisakhi Mondal, a student under Professor Kumaravel.
Decoding glioblastoma
In this study, the group, in collaboration with National Institute of Mental Health and Neurosciences (NIMHANS) and Sri Sathya Sai Institutes of Higher Medical Sciences, attempted to answer the widely pondered questions — What makes glioblastoma so lethally different from other tumours and what genes are dysregulated in this grade of tumour? To answer these, they used an integrated genome-wide DNA methylation analysis to compare differences of gene expression regulation between an aggressive form of glioblastoma (grade IV) and a lesser grade tumour (grade II). Gene expression is a tightly controlled process; certain parts of DNA can be modified to regulate gene expression. Since these changes occur at a region of DNA next to the sequences that actually code for genes, this form of regulation is termed ‘epigenetic regulation’. Specific enzymes add methyl groups to specific portions of promoters cause ‘silencing’ of genes. The technique used in the study also defines the methylation or ‘silenced’ state of promoter regions in glioblastoma and a grade II tumour.
The group identified a gene called fibromodulin (FMOD) among 350 genes unique to glioblastoma, which was sparsely methylated than the lower grade tumour tissues. In normal healthy individuals, FMOD protein is seen in large amounts in connective tissue but very little in normal brain. However, in glioblastoma FMOD levels increase due to loss of promoter methylation. The FMOD protein was previously reported by work from their lab to have a good prognosis when ‘silenced’.
Next, they turned their attention to the deeper question about fibromodulin’s modus operandi — how does fibromodulin aid glioblastoma in donning a metastatic avatar? They conducted experiments which silenced FMOD expression and studied gene sets that were affected most profoundly by the protein’s absence. Their analysis revealed that elements of the cellular cytoskeleton are most affected. Therefore, this hints about FMOD’s role in movement of glioma cells and by extrapolation, tumour cell migration.
Therapeutic interventions
Based on these results, it was hypothesised that FMOD may be needed for glioma cell migration and to prove this supposition, FMOD was silenced in FMOD overexpressing cells and invasive or migration capacity of these cells was tested using different in vitro assays, a type of scientific test that is performed in a laboratory. They also analysed one of the cytoskeletal elements, actin, in presence and absence of FMOD which revealed abrogation in actin function in the absence of FMOD to demonstrate its effects on cytoskeletal functions. In addition, they carried out several experiments to show that several molecules of the identified signalling pathway are, indeed, in attendance in the cancerous condition. All these results point towards FMOD’s role in making glioblastoma aggressively metastatic.
These results suggested that FMOD experiences a relaxed epigenetic regulation (less methylation) in glioblastoma and it ultimately gifts glioma with increased migration capacity and that the FMOD promoter methylation and transcript levels are independent predictors of survival in glioblastoma. Finally, the group concludes that fibromodulin may be used as target for therapeutic intervention to improve survival in glioblastoma. “In short, FMOD promoter methylation positively correlates with favourable prognosis and high FMOD transcript levels predicted poor prognosis in Glioblastoma,” divulges Baisakhi.