Crocetin treatment differentially changed the expression of
genes in the hippocampi of aged mice to bring about a change in memory
behavior
To understand the molecular basis of changes observed in the memory
behavior of treated mice, we isolated the hippocampi from the brain of
mice and sequenced the whole transcriptome. To achieve greater accuracy
in transcriptome sequencing, we used a depth of 40 million reads per
sample. We conducted PCA analysis to compare the control and
crocetin-treated groups. The results revealed significant insights into
the variance and underlying patterns within the datasets. The initial
nine principal components (PC1 to PC9) accounted for 84.06% of the
total variance, suggesting potential treatment-related effects (Figure
2A & B). Further, differential gene expression analysis revealed that
out of 22,096 protein-coding genes, 154 genes were differentially
expressed (Figure 2C). A detailed differential gene expression list is
provided as supplementary spreadsheet SS1.
We performed a hierarchical clustering to ensure to distinguish the
upregulated and downregulated genes. We found a significant upregulation
of Bdnf, Gabbr2, Gad2, and Drosha that correlated to the improved brain
function and behavior of treated mice (Figure 2D and Supplementary
Figure S3). Further, some of the genes downregulated after crocetin
treatment could also be linked to improvement in brain function, these
included Hck, Amigo3, Top1mt, and Lcp1 (Figure 2E).
Further analysis revealed that mitochondrial genes belonging to
different complexes of ETC were significantly upregulated. The
upregulated genes included ND1, ND2, ND4, ND4L, ND5, and ND6 related to
NADH dehydrogenase from complex I, CYTB from complex III, Uqcrq from
complex IV, and ATP6 and ATP8 from complex V (Figure 2F). Few more ETC
genes, such as ND3, COX1, COX2, and COX3, were also found upregulated,
though non-significantly (Supplementary Spreadsheet SS1).