Ht31, a Protein Kinase A Anchoring Inhibitor, Induces Robust Cholesterol Efflux and Reverses Macrophage Foam Cell Formation through ATP-binding Cassette Transporter A1

Abstract

Macrophage foam cell is the predominant cell type in atherosclerotic lesions. Removal of excess cholesterol from macrophages thus offers effective protection against atherosclerosis. Here we report that a protein kinase A (PKA)-anchoring inhibitor, st-Ht31, induces robust cholesterol/phospholipid efflux, and ATP-binding cassette transporter A1 (ABCA1) greatly facilitates this process. Remarkably, we found that st-Ht31 completely reverses foam cell formation, and this process is ABCA1-dependent. The reversal is also accompanied by the restoration of well modulated inflammatory response to LPS. There is no detectable toxicity associated with st-Ht31, even when cells export up to 20% cellular cholesterol per hour. Using FRET-based PKA biosensors in live cells, we provide evidence that st-Ht31 drives cholesterol efflux by elevating PKA activity specifically in the cytoplasm. Furthermore, ABCA1 facilitates st-Ht31 uptake. This allows st-Ht31 to effectively remove cholesterol from ABCA1-expressing cells. We speculate that de-anchoring of PKA offers a novel therapeutic strategy to remove excess cholesterol from lipid-laden lesion macrophages.

ABCA1 Protein Enhances Toll-like Receptor 4 (TLR4)-stimulated Interleukin-10 (IL-10) Secretion through Protein Kinase A (PKA) Activation

“…1). Consistent with previous findings including ours (3,18), ABCA1 ϩ/ϩ BMDM (WT) secreted fewer proinflammatory cytokines, such as TNF-␣ and IL-12p40 (Fig. 1A), in comparison with ABCA1 Ϫ/Ϫ BMDM.…”

The Interaction of ApoA-I and ABCA1 Triggers Signal Transduction Pathways to Mediate Efflux of Cellular Lipids

“…In addition, Bortnick et al found that cAMP treatment substantially increased the mRNA levels of ABCA1 in J774 and elicited mouse macrophages (46). It is worth noting that increasing cytosolic PKA activity by a membrane-permeable peptide inhibitor can even reverse the formation of macrophage foam cell through an ABCA1-dependent manner (65). There is a need for more critical evaluation in animal models and the clinic, however, of other signaling pathways and the different functionalities of HDL.…”

“…This allows A-kinase anchoring proteins to regulate the amplitude and duration of PKA activation locally. Loretta Ma et al report that st-Ht31, a membrane permeable peptide inhibitor of PKA anchoring, increases cytosolic PKA activity and robustly exports cholesterol as microparticles (65).…”

Molecular Biology of Atherosclerosis

“…This property was recently utilized to examine efflux of cholesterol to APOB-deficient serum with or without incubation of free cholesterol-loaded macrophages with a cAMP analog (1038). Active PKA may cause release of cholesterol as microparticles by an unknown mechanism which is greatly facilitated by ABCA1 (455,1099,2088). Increasing intracellular cAMP by pharmacological means appears to increase APOA1-mediated cholesterol removal from macrophages and may even increases plasma HDL-C levels (2087).…”