TGFB1 and Alzheimer disease: While the AD astrocyte subcluster called a1 in this study upregulated genes involved in ribosomal, mitochondrial, neurone differentiation and heat shock responses, the AD astrocyte subcluster called a2 downregulated these processes and upregulated genes involved in transforming growth factor β (TGF-β) signalling and immune responses (Table 1).