The male sex steroid, testosterone (T), is synthesized from cholesterol in the testicular Leydig cell under control of the pituitary gonadotropin LH. Unlike most cells that use cholesterol primarily for membrane synthesis, steroidogenic cells have additional requirements for cholesterol, because it is the essential precursor for all steroid hormones. Little is known about how Leydig cells satisfy their specialized cholesterol requirements for steroid synthesis. We show that in mice with a unique hypomorphic androgen mutation, which disrupts the feedback loop governing T synthesis, that genes involved in cholesterol biosynthesis/uptake and steroid biosynthesis are up-regulated. We identify LH as the central regulatory molecule that controls both steroidogenesis and Leydig cell cholesterol homeostasis in vivo. In addition to the primary defect caused by high levels of LH, absence of T signaling exacerbates the lipid homeostasis defect in Leydig cells by eliminating a short feedback loop. We show that T signaling can affect the synthesis of steroids and modulates the expression of genes involved in de novo cholesterol synthesis. Surprisingly, accumulation of active sterol response element-binding protein 2 is not required for up-regulation of genes involved in cholesterol biosynthesis and uptake in Leydig cells.

TLR7 activation is implicated in the pathogenesis of systemic lupus erythematosus (SLE). Mice that overexpress TLR7 develop a lupus-like disease with autoantibodies and glomerulonephritis and early death. To determine whether degradation of the TLR7 ligand, RNA, would alter the course of disease, we created RNase A transgenic (Tg) mice. We then crossed the RNase Tg to TLR7 Tg mice to create TLR7 x RNase double Tg (DTg) mice. DTg mice had a significantly increased survival associated with reduced activation of T and B lymphocytes and reduced kidney deposition of IgG and C3. We observed massive hepatic inflammation and cell death in TLR7 Tg mice. In contrast, hepatic inflammation and necrosis were strikingly reduced in DTg mice. These findings indicate that high concentrations of serum RNase protect against immune activation and inflammation associated with TLR7 stimulation and that RNase may be a useful therapeutic strategy in the prevention or treatment of inflammation in SLE and, possibly, liver diseases.

Hepatic lipase (HL)-mediated lipoprotein hydrolysis provides free fatty acids for energy, storage, and nutrient signaling and may play a role in energy homeostasis. Because HL-activity increases with increased visceral fat, we hypothesized that increased HL-activity favors weight gain and obesity and consequently, that HL deficiency would reduce body fat stores and protect against diet-induced obesity. To test this hypothesis, we compared wild-type mice (with endogenous HL) and mice genetically deficient in HL with respect to daily body weight and food intake, body composition, and adipocyte size on both chow and high-fat (HF) diets. Key determinants of energy expenditure, including rate of oxygen consumption, heat production, and locomotor activity, were measured by indirect calorimetry. HL-deficient mice exhibited reduced weight gain on both diets (by 32%, chow; by 50%, HF; both P < 0.0001, n = 6-7 per genotype), effects that were associated with reduced average daily food intake (by 22-30% on both diets, P < 0.0001) and a modest increase in the rate of oxygen consumption (by 25%, P < 0.003) during the light cycle. Moreover, in mice fed the HF diet, HL deficiency reduced both body fat (by 30%, P < 0.0001) and adipocyte size (by 53%, P < 0.01) and fully prevented the development of hepatic steatosis. Also, HL deficiency reduced adipose tissue macrophage content, consistent with reduced inflammation and a lean phenotype. Our results demonstrate that in mice, HL deficiency protects against diet-induced obesity and its hepatic sequelae. Inhibition of HL-activity may therefore have value in the prevention and/or treatment of obesity.

Objective-Increased expression of human hepatic lipase (HL) or a catalytically inactive (ci) HL clears plasma cholesterol in mice deficient in low-density lipoprotein receptors (LDLr) and murine HL. We hypothesized that increased expression of both HL and ciHL reduces atherosclerosis in these mice. Methods and Results-Mice deficient in both LDLr and murine HL, alone or transgenically expressing similar levels of either human HL or ciHL, were fed a high-fat, cholesterol-enriched "Western" diet for 3 months to accelerate the development of atherosclerosis. Levels of plasma lipids, insulin, glucose, and liver enzymes were measured monthly, and aortic atherosclerosis was quantitated after 3 months. Plasma insulin, glucose, and liver enzyme levels did not differ significantly from controls. After 3 months, expression of HL reduced plasma cholesterol by 55% to 65% and reduced atherosclerosis by 40%. Surprisingly, expression of ciHL did not reduce plasma cholesterol or atherosclerosis. Key Words: hepatic lipase Ⅲ atherosclerosis Ⅲ bridging function Ⅲ fatty liver Ⅲ mouse models H uman hepatic lipase (HL) plays a central role in lipid metabolism and atherosclerosis. 1,2 HL is a secreted, multifunctional enzyme produced by the liver. In the liver, it binds to heparan sulfate proteoglycans (HSPG) on hepatocyte and endothelial cell surfaces and hydrolyzes triglycerides and phospholipids in lipoproteins yielding particles that are optimal for receptor-mediated uptake. 2-5 HL functions as a bridge between lipoproteins and cell-surface HSPG, thereby facilitating receptor-mediated lipoprotein uptake by the lowdensity lipoprotein receptor (LDLr) and the LDLr-related protein (LRP). [5][6][7][8] The bridging also facilitates selective cholesterol uptake by the scavenger receptor B1. 9,10 The role of HL in atherosclerosis is controversial. 11,12 Some studies support a pro-atherogenic role. For example, HL mediates production of small dense LDL (part of the atherogenic lipid profile). HL activity is elevated in males and postmenopausal women, both at increased risk for atherosclerosis. [13][14][15][16] In rabbits transgenic for human apoB, HL expression results in atherogenic small dense LDL particles. 17 In female apoE-deficient mice (an atherosclerosis model), atherosclerosis was reduced when the mouse (m) HL gene was deleted by gene targeting. 18 Furthermore, adding mHL back to macrophages (using bone marrow transplantation) in the apoE-deficient and mHL-deficient mice actually increased atherosclerosis. 19 Other studies support a protective role for HL. In humans, HL reduces atherogenic remnant lipoproteins and increases production of high-density lipoprotein (HDL) 3 and pre-␤ 1 HDL, both avid acceptors of free cholesterol. 20 -24 In HL transgenic mice, aortic cholesterol was decreased. 25 In mice overexpressing HL, cholesterol levels were significantly lower. 5,26 Likewise, animal models overexpressing a catalytically inactive variant of HL (ciHL) (reflecting the bridging function of HL) also had lower cholesterol levels, sugg...

Hepatic lipase clears plasma cholesterol by lipolytic and nonlipolytic processing of lipoproteins. We hypothesized that the nonlipolytic processing (known as the bridging function) clears cholesterol by removing apoB-48-and apoB-100-containing lipoproteins by whole particle uptake. To test our hypotheses, we expressed catalytically inactive human HL (ciHL) in LDL receptor deficient "apoB-48-only" and "apoB-100-only" mice. Expression of ciHL in "apoB-48-only" mice reduced cholesterol by reducing LDL-C (by 54%, 46 ؎ 6 vs. 19 ؎ 8 mg/dl, P Ͻ 0.001). ApoB-48 was similarly reduced (by 60%). The similar reductions in LDL-C and apoB-48 indicate cholesterol removal by whole particle uptake. Expression of ciHL in "apoB-100-only" mice reduced cholesterol by reducing IDL-C (by 37%, 61 ؎ 19 vs. 38 ؎ 12 mg/dl, P Ͻ 0.003). Apo-B100 was also reduced (by 27%). The contribution of nutritional influences was examined with a high-fat diet challenge in the "apoB-100-only" background. On the high fat diet, ciHL reduced IDL-C (by 30%, 355 ؎ 72 vs. 257 ؎ 64 mg/dl, P Ͻ 0.04) but did not reduce apoB-100. The reduction in IDL-C in excess of apoB-100 suggests removal either by selective cholesteryl ester uptake, or by selective removal of larger, cholesteryl ester-enriched particles. Our results demonstrate that the bridging function removes apoB-48-and apoB-100-containing lipoproteins by whole particle uptake and other mechanisms.-Dichek, H. L., K. Qian, and N. Agrawal. The bridging function of hepatic lipase clears plasma cholesterol in LDL receptor-deficient "apoB-48-only" and "apoB-100-only" mice. Human hepatic lipase (HL) is a central component of lipoprotein metabolism (1, 2). HL is synthesized and secreted by the liver, where it is anchored to the surface of hepatocytes and sinusoidal endothelial cells via heparan sulfate proteoglycans (HSPGs) (3-6). HL hydrolyzes triglycerides and phospholipids in remnants (chylomicron remnants and IDL) and LDL to yield particles that are depleted in triglycerides and phospholipids and are more optimal for receptor-mediated uptake (2, 7-9). HL may also play a role in reverse cholesterol transport by hydrolyzing phospholipids in HDL, which converts HDL2 to HDL3 (10, 11).The significant role of HL in lipoprotein metabolism is apparent from human studies and data generated in animals. For example, plasma of HL-deficient patients contains high levels of apolipoprotein B (apoB)-containing lipoproteins and HDL (12-17). Infusion of anti-HL antibodies in rats and monkeys increases levels of apoBcontaining lipoproteins and HDL (18)(19)(20). Expression of moderate and high levels of wild-type HL in mice and rabbits reduces levels of apoB-containing lipoproteins and HDL (6,(21)(22)(23)(24). Taken together, these studies indicate a major role for HL in determining the plasma levels of apoB-containing lipoproteins and HDL.HL regulates plasma levels of apoB-containing lipoproteins using both catalytic and bridging functions (6,25). In particular, wild-type HL (reflecting both catalytic and bridging func...