The neuropathy, retinopathy, and kidney disease that develop with the insulin deficiency of Type 1 diabetes and severe Type II diabetes are highly associated with a tissue depletion of 20- and 22-carbon (n-6) and (n-3) polyunsaturated fatty acids (HUFA). Tissue HUFA levels are largely dependent on the desaturation of dietary 18-carbon precursors by delta-6 (D6ase) and delta-5 desaturases (D5ase). The activity of D6ase and D5ase is greatly reduced in diabetes. Our long-term goal is to determine how diabetes suppresses D6ase and D5ase expression. Our pioneering work with the human D6ase and D5ase genes revealed that the regulation of these genes and the structure of the proteins have several unique features. The most unique discovery was the identification of a transcript (i.e. RevD5ase) that was synthesized from the opposite strand of D5ase, and appears to possess the ability to suppress D5ase mRNA levels. We now hypothesize that RevD5ase functions as an anti-sense suppressor of D5ase expression. We further propose that insulin insufficiency suppresses the HUFA biosynthetic pathway by increasing the tissue content of RevD5ase mRNA. Our prior work also indicated that hepatic D6ase and D5ase gene expression is induced several fold by PPARa activators. Thus, a corollary hypothesis is that PPARa activators suppress RevD5ase gene expression, which in turn enhances D5ase expression and overall HUFA output.
The specific aims are to determine: (a) the molecular mechanisms by which RevD5ase suppresses D5ase expression and HUFA synthesis and utilize this information to determine if the mechanism of RevD5ase involves translation and/or transcription interference; (b) hormonal and nutrient regulators of RevD5ase expression in hepatic and non-hepatic tissues; (c) molecular mechanisms by which PPARa activators induce hepatic D6ase and D5ase expression, and determine if this induction extends to non-hepatic tissues and if the induction can correct the HUFA deficiency of diabetes; and (d) the kinetic properties of the D6ase and D5ase enzymes and examine the function of the cytochrome b5-like and histidine rich domains of the D6ase and D5ase. The ultimate goal is to use this information in developing molecular and cellular intervention strategies for improving HUFA status of diabetics.
