Table 2.

Evolutionary conservation of gene expression changes during brain ageing

Gene category	Human (brain)	Rhesus macaque (brain)	Rat (brain)	Mouse (brain)	Fly (organism)	Worm (organism)
Stress response	↑	↑	↑	↑	↑	↑
Mitochondria	↓	↓	↓	↓↑	↓	↓
Neural plasticity/synaptic function	↓	↓	↓	↓	–	–
Inhibitory interneuron function	↓	↓	–	–	–	–
Ubiquitin–proteasome pathway	↓	↓	–	↓	–	–
Immune/inflammatory response	↑	–	↑	↑	↑	–
Metal ion homeostasis	↑	–	↑	–	–	–
Myelin-related proteins	↑	–	↑	–	–	–
Glial genes	↑	–	↑	–	–	–

Some gene categories, such as those involved in stress responses and mitochondrial function, show conserved changes during ageing, whereas others, such as inhibitory interneuron function, exhibit primate-specific changes. An upward arrow indicates that expression increases with age; a downward arrow indicates that expression decreases with age; and a dash indicates that no change in expression with age is detected. In the ageing mouse brain, different subsets of mitochondrial genes are either age-upregulated or age-downregulated (13).