Laminins 2 (α2β1γ1, Lm-211) and 8 (α4β1γ1, Lm-411) are synthesized and secreted by tooth pulp fibroblasts and differentially promote neurite outgrowth from trigeminal ganglion sensory neurons

The tooth pulp innervation originates from the trigeminal ganglion (TG) and represents an illustrative example of tissue targeting by sensory nerves. Pulpal fibroblasts strongly promote neurite outgrowth from TG neurons in vitro. In the present study, we have investigated the possible participation of laminins (LNs), potent neuritogenic extracellular matrix components. Immunohistochemistry of human tooth pulp demonstrated expression of LN α1, α2, α4, α5, β1 and γ1, and laminin-binding integrin α3, α6, β1 and β4 chains in nerves. Though faintly stained for laminins in situ, pulpal fibroblasts reacted, once cultured and permeabilized, with antibodies to LN α2, α4, β1 and γ1 chains by flow cytometry. The cells also expressed the corresponding mRNAs and were able to assemble and secrete LN-2 (α2β1γ1, Lm-211) and LN-8 (α4β1γ1, Lm-411). LN-8 displayed a chondroitin sulphate (CS) modification in its α4 chain. In functional assays, mouse LN-1 (α1β1γ1, Lm-111) and recombinant human (rh) LN-8, but not native or rhLN-2, strongly promoted neurite outgrowth from TG neurons, mimicking the effect of cultured pulp fibroblast. Altogether, the results indicate that LN-2 and LN-8 are synthesized by tooth pulp fibroblasts and differentially promote neurite outgrowth from TG neurons. LN-8 may contribute to sensory innervation of teeth and other tissues during development and/or regeneration.