Expression of BMP7 is associated with resistance to diabetic stress: Comparison among mouse salivary glands

We determined mRNA levels of bone morphogenetic protein 7 (BMP7), a growth and differentiation factor belonging to the transforming growth factor-β superfamily, in the salivary glands of mice with streptozotocin (200 mg/kg, i.p.)-induced diabetes. We also examined the effects of BMP7 on secretion of saliva and degenerative change in salivary glands in diabetic mice. In normal mice, BMP7 mRNA levels were high in the submandibular gland and low in the parotid gland, while in diabetic mice, levels were significantly decreased in the parotid gland, but not in the submandibular gland. No significant difference was observed in mRNA levels of BMP receptors between normal and diabetic mice. In diabetic mice, pilocarpine (4 mg/kg, i.p.)-stimulated salivary secretion showed a remarkable decrease in both parotid and submandibular gland, although degree of reduction was smaller in the latter. Notable degeneration with vacuolation and atrophy was also found in parotid gland, whereas degeneration of submandibular gland was slight. Administration of BMP7 (50 and 100 µg/kg, i.v.) in diabetic mice induced a significant increase in salivary secretion, with rate of recovery higher in parotid gland than in submandibular gland. In diabetic mice, BMP7 also exhibited a powerful protective effect in degenerated salivary gland, especially in parotid gland. These results suggest that BMP7 acts to prevent diabetic damage in salivary gland, and that its cytoprotective effect is closely correlated with mRNA levels in tissue.