Glucose and scyllo-inositol impair phosphoinositide hydrolysis in the 10.5-day cultured rat conceptus: a role in dysmorphogenesis?
Culture of the postimplantation rat conceptus from gestational day 9.5-10.5 in media supplemented with d-glucose or scyllo-inositol decreases tissue myo-inositol and phosphoinositides with a concomitant increase in dysmorphogenesis. A number of mitogenic agents initiate cellular proliferation and differentiation through receptors coupled to phosphoinositide hydrolysis. To test whether the decrease in conceptus phosphoinositides is associated with a reduced phosphoinositide hydrolytic response, we developed a protocol to stimulate phosphoinositide hydrolysis. Phosphoinositide hydrolysis was monitored by measurement of [3H]inositol phosphates after preincubation in serum free media. We examined the ability of serum, platelet-derived growth factor (PDGF), epidermal-derived growth factor (EGF), insulin-like growth factor 1 (IGF-1), insulin-like growth factor 2 (IGF-2), endothelin-1 (ET-1), and endothelin-2 (ET-2), to stimulate phosphoinositide hydrolysis. As measured by [3H]inositol monophosphate ([3H]InsP1) accumulation, normal rat seru, ET-1, and ET-2 stimulated phosphoinositide hydrolysis 47%, 420%, and 154% above the basal rate observed in serum free controls. EGF stimulated a statistically insignificant 15% increase while PDGF, IGF-1, or IGF-2 were without effect. We further characterized ET-1 stimulated phosphoinositide hydrolysis. Dose-response studies disclosed that incremental increases in [3H]InsP1 (129-420%) are observed over a concentration range of 10-1,000 nM. Maximal stimulation was not reached even at 1,000 nM. Temporally [3H]InsP1 and [3H]InsP3 levels increased linearly during incubation periods of 15-60 min. We further analyzed ET-1 stimulated phosphoinositide hydrolysis in 10.5-day conceptuses cultured for 24 hr in media containing high concentrations of glucose (23.3-56.6 mM) or scyllo-inositol (0.55, 5.5 mM). Under these dysmorphogenic conditions that concomitantly decrease the phosphoinositide precursor pool the response to ET-1 was blunted 28-76% for glucose and 29-65% for scyllo-inositol. This suggests that the effect of glucose and scyllo-inositol on lowering phosphoinositide precursor pools also results in a decrease in the response to agonists using the inositol/lipid intracellular pathway. This impaired signaling response may contribute to initiating dysmorphogenic events in diabetic embryopathy.
Strieleman
P J
PJ
Center for Endocrinology, Metabolism and Nutrition, Northwestern University, Chicago, Illinois 60611.
Metzger
B E
BE
D000818:Animals; D000013:Congenital Abnormalities / Q000209:etiology*; D004622:Embryo, Mammalian / Q000187:drug effects* / Q000378:metabolism; D005314:Embryonic and Fetal Development / Q000187:drug effects; D005260:Female; D005865:Gestational Age; D005947:Glucose / Q000494:pharmacology*; D006868:Hydrolysis; D066298:In Vitro Techniques; D007294:Inositol / Q000494:pharmacology*; D007700:Kinetics; D008934:Mitogens / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism*; D011247:Pregnancy; D011254:Pregnancy in Diabetics; D051381:Rats; D015398:Signal Transduction; D013237:Stereoisomerism
D008934:Mitogens; D010716:Phosphatidylinositols; C009217:scyllitol; D007294:Inositol; D005947:Glucose