INSULIN-LIKE GROWTH FACTOR BINDING PROTEIN-5 DEPENDS ON IGF-I TO PROMOTE AXONAL GROWTH OF OLFACTORY NEURONS

Jingjing Zhang*, Qiong Wang**, Shurui Li***, Feng Zhao**, Naijia Liu****, Xilian Feng****, Xin Wen****, #

*Department of Otolaryngology and Head Surgery, Gansu University of CM Affiliated Hospital of Gansu University of CM, Lanzhou, PR China - **Department of Neurology, Gansu University of CM Affiliated Hospital of Gansu University of CM, Lanzhou, PR China - ***Department of Disinfection, University of CM Affiliated Hospital of Gansu University of CM, Lanzhou, PR China - ****Department of Acupuncture and Moxibustion, University of CM Affiliated Hospital of Gansu University of CM, Lanzhou, PR China

Objective: To explore the mechanism of insulin-like growth factor binding protein-5 (IGFBP-5) depending on IGF-I to promote axonal growth in olfactory neurons. 

Methods: Primary olfactory receptor neurons of olfactory ensheathing cells, astrocytes and Schwann cells were cultured. The primary cultured olfactory neurons were divided into a control group, an IGFBP-5 group, an IGFBP-5 antibody intervention group and an IGFBP-5+PPP group. The growth model of olfactory neurites was established. Immunocytochemistry and DAB were used. The expression of IGFBP-5 in olfactory ensheathing cells (OECs), Schwann cells (SCs), astrocytes (ACs) and olfactory bulbs (OB), the effect of IGFBP-5 on the axon growth of olfactory neurons, the effect of IGFBP-5 antibody on the axon growth of olfactory neurons and the expression of insulin-like growth factor binding protein-5 (IGFBP-5) through pancreas were analysed using a colour-rendering method. Insulin growth factor-I (IGF-I) mediates axonal growth of olfactory neurons. 

Results: IGFBP-5 was highly expressed in OECs, but weakly expressed in SCs and ACs. IGFBP-5 is highly expressed in the olfactory nerve layer of OB, and the lower the expression is, the concentration gradient appears. IGFBP-5 could promote the growth of olfactory neurons axons, and the axons of olfactory neurons in 500 ng/ml group were significantly longer than those in 10 ng/ml group and 100 ng/ml group (P<0.05). The axon length of olfactory neurons in Anti-IGFBP-5 group was significantly shorter than that in IGFBP-5 group and control group (P<0.05). The length of olfactory axon in IGFBP-5 + PPP group was significantly shorter than that in IGFBP-5 group and control group (P<0.05). 

Conclusion: OECs can promote the growth of ORNs axons by secreting IGFBP-5 depending on IGF-I, suggesting that IGFBP-5 may be involved in the mediation of OECs promoting the growth of ORNs axons.