Background and Aims: Sporadic colorectal cancer (CRC) development is a sequential process showing age-dependency,
uncontrolled epithelial proliferation and decreased apoptosis. During juvenile growth cellular proliferation and apoptosis
are well balanced, which may be perturbed upon aging. Our aim was to correlate proliferative and apoptotic activities in
aging human colonic epithelium and colorectal cancer. We also tested the underlying molecular biology concerning the
proliferation- and apoptosis-regulating gene expression alterations.
Materials and Methods: Colorectal biopsies from healthy children (n1 = 14), healthy adults (n2 = 10), adult adenomas
(n3 = 10) and CRCs (n4 = 10) in adults were tested for Ki-67 immunohistochemistry and TUNEL apoptosis assay. Mitosis- and
apoptosis-related gene expression was also studied in healthy children (n1 = 6), adult (n2 = 41) samples and in CRC (n3 = 34)
in HGU133plus2.0 microarray platform. Measured alterations were confirmed with RT-PCR both on dependent and
independent sample sets (n1=6, n2=6, n3 = 6).
Results: Mitotic index (MI) was significantly higher (p,0.05) in intact juvenile (MI = 0.3360.06) and CRC samples
(MI = 0.4260.10) compared to healthy adult samples (MI = 0.1560.06). In contrast, apoptotic index (AI) was decreased in
children (0.1360.06) and significantly lower in cancer (0.0660.03) compared to healthy adult samples (0.1760.05). Eight
proliferation- (e.g. MKI67, CCNE1) and 11 apoptosis-associated genes (e.g. TNFSF10, IFI6) had altered mRNA expression both
in the course of normal aging and carcinogenesis, mainly inducing proliferation and reducing apoptosis compared to
healthy adults. Eight proliferation-associated genes including CCND1, CDK1, CDK6 and 26 apoptosis-regulating genes (e.g.
SOCS3) were differently expressed between juvenile and cancer groups mostly supporting the pronounced cell growth in
CRC.
Conclusion: Colorectal samples from children and CRC patients can be characterized by similarly increased proliferative and
decreased apoptotic activities compared to healthy colonic samples from adults. Therefore, cell kinetic alterations during
colorectal cancer development show uncontrolled rejuvenescence as opposed to the controlled cell growth in juvenile
colonic epithelium