Page 123 - GPD-4-2

Gene & Protein in Disease Pediatric glioma circadian clock genes

treating both stages of cancer. Additional studies should from studies capable of spatially resolving gene activity
examine clock gene expression in recurrent tumors of within tumor regions that are known to differ in their
other glioma types. Furthermore, clock gene expression stem cell properties. 101,102 It is also unclear whether the
should be evaluated in recurrent tumors of glioma types circadian clocks in the sampled tumors were disturbed or
not thoroughly examined here, such as DIPG, another suppressed by the cancer or, alternatively, the cancer was
high-grade pediatric tumor that appears to be related to facilitated by a disrupted clock within the tissue of origin.
GBM. 36 Much still needs to be explored concerning the circadian
clocks functioning within tumors in situ and how they
4.3. Evaluating clock gene activity in pediatric interact with the rest of the body, altering rhythms within
gliomas at different times of day and beyond the cancer cells.
This study did not attempt to detect changes in circadian
rhythms in the various glioma groups relative to non-tumor 4.4. Clock gene activity elevated in pediatric glioma
tissue, which might provide insight into the observed subtypes
differences in gene expression. What was examined was Examining the relative expression of the clock genes across
any significant departures in expression above or below four recognized MB subtypes provided a detailed view of
that in equivalent normal tissue. To characterize any which subtypes may rely on these genes either in circadian
circadian rhythms in the pediatric glioma tissue, the tumor timing or in a non-clock function. In the bulk tumor data,
cells would, ideally, need to be maintained in vitro, perhaps the Group 4 subtype had elevated expression of seven genes
as tumorsphere cultures, and then synchronized through relative to the other subtypes, and Group 3 had two. These
currently available methods so that the cells oscillate results were supported by the scRNA-seq analysis that
together with a common phase of the circadian cycle. As revealed significantly higher expression of circadian clock
99
with adult glioma cells, expression would then be assayed genes in G3 and G4 than in the SHH and WNT subtypes.
in these patient-derived cells at intervals to measure Interestingly, elevated TIMELESS expression was also
multiple circadian cycles. observed more frequently in the G3 and G4 subtypes
A previous study by Huang et al., comparing of the bulk tumor studies, which, along with its higher
100
microarray-assayed transcriptomes of pediatric and expression relative to normal tissue in several of the other
adult MB tumors, found by GSEA that the pediatric glioma datasets examined, further argues for its value in
cells have upregulated expression of a gene set described developing novel treatment strategies. Nevertheless, the
as “entrainment of circadian clock by photoperiod” TIMELESS expression did not appear to be elevated relative
(GO:0043153). Several of the members of this probe gene to the rest of the circadian gene set in the pHGG and MB
set were also tested in our study (CRY1, CRY2, PER1, PER2, scRNA-seq results. Along with nearly all core clock genes,
and PER3). Like their results with MB tumor samples, TIMELESS was expressed in a larger percentage of the
we found that PER2 and PER3 were suppressed in adult malignant MB cells than the immune cells, although it is
GBM relative to normal tissue but not in the two pediatric not accurate to consider these stromal cells comparable
GBM datasets (Griesing, 2013 and Buczkowicz, 2014). to normal tissue because of the effects from the tumor
Furthermore, we detected a significant increase of CRY1 in microenvironment. An analysis of the spatial expression of
adult GBM, but not in pediatric GBM, which differs from TIMELESS protein within the tumor cell types is needed to
their MB results. It would be useful to test whether glioma determine whether its functions are promising targets for
cells use this gene set to entrain their circadian clocks to anticancer treatments.
daily oscillations in hormones, cytokines, nutrients, etc., Circadian clock genes should be examined for their
in their extracellular environment. Evidence supports the possible role in any of the critical cancer progression events
entrainment of GBM circadian clocks to daily oscillations involving G3 and G4 MB subtypes. G3 cells are considered
in blood cortisol. 11 the most aggressive of the four subtypes, whereas the SHH
It is unlikely that the tumor samples used to produce and WNT subtypes are associated with more favorable
transcriptomic data were collected from patients at a patient outcomes. 103,104 The G3 and G4 subtypes appear
consistent time of day, suggesting that the values could to be part of a continuum arising during development,
have fluctuated in response to influences from circadian as genes expressed in cells derived from specific neural
rhythms in gene expression. The extent of endogenous precursors are inappropriately regulated, leading to tumor
circadian rhythms in gene expression in pediatric tumor formation. Also, the G3 and G4 subtypes are more than
105
cell types remains unknown. Of course, these conclusions twice as likely to have metastasized before treatment than
that are drawn mostly from bulk tumor data would benefit are SHH and WNT tumors. Medulloblastoma cells are
106

Volume 4 Issue 2 (2025) 17 doi: 10.36922/gpd.4112