Methods of expressing LIM mineralization protein in non-osseous mammalian cells, such as stem cells or intervertebral disc cells (e.g., cells of the annulus fibrosus, or cells of the nucleus pulposus) are described. The methods involve transfecting the cells with an isolated nucleic acid comprising a nucleotide sequence encoding a LIM mineralization protein operably linked to a promoter. Transfection may be accomplished ex vivo or in vivo by direct injection of virus or naked DNA, or by a nonviral vector such as a plasmid. Expression of the LIM mineralization protein can stimulate proteoglycan and/or collagen production in cells capable of producing proteoglycyan and/or collagen. Methods for treating disc disease associated with trauma or disc degeneration are also described.