This invention generally relates to a composition and method of using recombinant microRNAs (miRNA) and their hairpin-like precursors (pre-miRNA) as therapeutic drugs for treating Alzheimer's diseases (AD). More specifically, the present invention relates to the use of man-made miRNA miR-302 precursors (pre-miR-302) for AD therapy in humans. These pre-miR-302 molecules can be mass produced in prokaryotes as a form of DNA expression-competent DNA vectors and/or hairpin-like RNAs. As prokaryotic cells do not transcribe or process hairpin-like RNAs, the present invention also teaches a method for expressing pre-miRNAs in prokaryotes, i.e. pro-miRNA, using a novel hairpin-like RNA transcription mechanism newly found in prokaryotes. Additionally, since miR-302 is a well-known embryonic stem cell (ESC)-specific factor in humans, our novel findings of this invention can be further used to advance the designs and development of novel regenerative medicine for treating many other ageing-related degenerative diseases, such as Parkinson's diseases, osteoporosis, diabetes, and cancers.