👤 Patricia G Yancey

Autophagy modulates lipid turnover, cell survival, inflammation, and atherogenesis. Scavenger receptor class B type I (SR-BI) plays a crucial role in lysosome function. Here, we demonstrate that SR-BI regulates autophagy in atherosclerosis. SR-BI deletion attenuated lipid-induced expression of autophagy mediators in macrophages and atherosclerotic aortas. Consequently, SR-BI deletion resulted in 1.8- and 2.5-fold increases in foam cell formation and apoptosis, respectively, and increased oxidized LDL-induced inflammatory cytokine expression. Pharmacological activation of autophagy failed to reduce lipid content or apoptosis in Sr-b1-/- macrophages. SR-BI deletion reduced both basal and inducible levels of transcription factor EB (TFEB), a master regulator of autophagy, causing decreased expression of autophagy genes encoding VPS34 and Beclin-1. Notably, SR-BI regulated Tfeb expression by enhancing PPARα activation. Moreover, intracellular macrophage SR-BI localized to autophagosomes, where it formed cholesterol domains resulting in enhanced association of Barkor and recruitment of the VPS34-Beclin-1 complex. Thus, SR-BI deficiency led to lower VPS34 activity in macrophages and in atherosclerotic aortic tissues. Overexpression of Tfeb or Vps34 rescued the defective autophagy in Sr-b1-/- macrophages. Taken together, our results show that macrophage SR-BI regulates autophagy via Tfeb expression and recruitment of the VPS34-Beclin-1 complex, thus identifying previously unrecognized roles for SR-BI and potentially novel targets for the treatment of atherosclerosis. Show less

Recessive inheritance of mutations in ceroid neuronal lipofuscinosis type 3 (CLN3) results in juvenile neuronal ceroid lipofuscinosis (JNCL), a childhood neurodegenerative disease with symptoms including loss of vision, seizures, and motor and mental decline. CLN3p is a transmembrane protein with undefined function. Using a Cln3 reporter mouse harboring a nuclear-localized bacterial beta-galactosidase (beta-Gal) gene driven by the native Cln3 promoter, we detected beta-Gal most prominently in epithelial cells of skin, colon, lung, and kidney. In the kidney, beta-Gal-positive nuclei were predominant in medullary collecting duct principal cells, with increased expression along the medullary osmotic gradient. Quantification of Cln3 transcript levels from kidneys of wild-type (Cln3(+/+)) mice corroborated this expression gradient. Reporter mouse-derived renal epithelial cultures demonstrated a tonicity-dependent increase in beta-Gal expression. RT-quantitative PCR determination of Cln3 transcript levels further supported osmoregulation at the Cln3 locus. In vivo, osmoresponsiveness of Cln3 was demonstrated by reduction of medullary Cln3 transcript abundance after furosemide administration. Primary cultures of epithelial cells of the inner medulla from Cln3(lacZ/lacZ) (CLN3p-null) mice showed no defect in osmolyte accumulation or taurine flux, arguing against a requirement for CLN3p in osmolyte import or synthesis. CLN3p-deficient mice with free access to water showed a mild urine-concentrating defect but, upon water deprivation, were able to concentrate their urine normally. Unexpectedly, we found that CLN3p-deficient mice were hyperkalemic and had a low fractional excretion of K(+). Together, these findings suggest an osmoregulated role for CLN3p in renal control of water and K(+) balance. Show less

Low levels of transgenic mouse apolipoprotein E (apoE) suppress atherosclerosis in apoE knockout (apoE-/-) mice without normalizing plasma cholesterol. To test whether this is due to facilitation of cholesterol efflux from the vessel wall, we produced apoA-I-/-/apoE-/- mice with or without the transgene. Even without apoA-I and HDL, apoA-I-/-/apoE-/- mice had the same amount of aorta cholesteryl ester as apoE-/- mice. Low apoE in the apoA-I-/-/apoE-/- transgenic mice reduced aortic lesions by 70% versus their apoA-I-/-/apoE-/- siblings. To define the free cholesterol (FC) efflux capacity of lipoproteins from the various genotypes, sera were assayed on macrophages expressing ATP-binding cassette transporter A1 (ABCA1). Surprisingly, ABCA1 FC efflux was twice as high to sera from the apoA-I-/-/apoE-/- or apoE-/- mice compared with wild-type mice, and this activity correlated with serum apoA-IV. Immunodepletion of apoA-IV from apoA-I-/-/apoE-/- serum abolished ABCA1 FC efflux, indicating that apoAI-V serves as a potent acceptor for FC efflux via ABCA1. With increasing apoE expression, apoA-IV and FC acceptor capacity decreased, indicating a reciprocal relationship between plasma apoE and apoA-IV. Low plasma apoE (1-3 x 10(-8) M) suppresses atherosclerosis by as yet undefined mechanisms, not dependent on the presence of apoA-I or HDL or an increased capacity of serum acceptors for FC efflux. Show less