Atherosclerotic cardiovascular disease remains the major cause of death in patients with type 1 and type 2 diabetes mellitus (T1DM, T2DM). Atherosclerosis arises from the retention of cholesterol-rich, apolipoprotein-B (apoB)-lipoproteins within the vessel wall. Importantly, diabetic patients suffer from a unique and typically neglected aspect of cardiovascular risk, namely, the striking persistence of intestinally derived apoB-lipoproteins, called `remnants,'in their plasma after each meal. The cause is a defect in hepatic clearance of these harmful particles. A major impediment in this area has been our ignorance regarding pathways for remnant uptake into the liver. A quarter century ago, hepatic uptake of remnants was shown to be independent of LDL receptors. This realization launched a long, difficult search for the responsible molecules. In 1991-1992, seminal work from our laboratory implicated heparan sulfate proteoglycans (HSPGs) in remnant lipoprotein uptake. Each HSPG molecule consists of a protein strand onto which the cell assembles sugar polymers, called heparan sulfate, that we showed could capture lipoproteins. In a major, recent breakthrough, we found that T2DM induces HSPG degradative enzymes in liver. Our central hypothesis is that the identification of compounds that accelerate uptake of atherogenic remnant lipoproteins into liver cells will substantially advance our physiologic understanding while also opening exciting, new avenues for potentially life-saving therapeutics in diabetes.
In Aim 1, we propose to develop screens for inducers of hepatocyte uptake of model remnant lipoproteins. Compound screens using whole-cell read-outs are the ideal approach to manage the biologic complexity of HSPG assembly.
Aim 1 a will automate and optimize our new fluorescent assay for HSPG-mediated uptake of model remnant lipoproteins, in preparation for moderate-throughput screening.
Aim 1 b will perform titration-based screening of three libraries of diverse, active compounds.
In Aim 2, we propose to evaluate hit compounds.
Aim 2 a will rule out artifacts, establish selectivity for HSPG-mediated uptake, and prioritize compounds.
Aim 2 b will determine the molecular effects of prioritized compounds. Based on our new data, our favored mechanism is inhibition of HSPG degradative enzymes.
Aim 2 c will define metabolic responses to enhanced uptake of remnants, to choose potential therapeutic leads. Overall, these proposed Aims will substantially advance our molecular knowledge of remnant lipoprotein clearance, as well as our ability to correct diabetic postprandial dyslipidemia. Our ultimate goal will be to avert the tremendous excess burden of cardiovascular disease in diabetes, to which postprandial dyslipidemia makes a substantial, and potentially avoidable, contribution.
Project relevance to public health Patients with diabetes mellitus suffer from fatal and disabling atherosclerotic cardiovascular disease that results in part from the striking persistence of harmful intestinally derived lipoproteins, called `remnants,'in their plasma after each meal. Based on our seminal work implicating a crucial role for heparan sulfate proteoglycans (HSPGs) in the rapid, healthy disposal of remnant lipoproteins by the liver, we now seek novel compounds to enhance HSPG display by hepatocytes and thereby accelerate the uptake of these harmful lipoproteins. The ultimate goal will be to avert the tremendous excess burden of cardiovascular disease in diabetes.
|Hassing, H Carlijne; Mooij, Hans; Guo, Shuling et al. (2012) Inhibition of hepatic sulfatase-2 in vivo: a novel strategy to correct diabetic dyslipidemia. Hepatology 55:1746-53|
|Chen, Keyang; Liu, Ming-Lin; Schaffer, Lana et al. (2010) Type 2 diabetes in mice induces hepatic overexpression of sulfatase 2, a novel factor that suppresses uptake of remnant lipoproteins. Hepatology 52:1957-67|