Cytochemical studies of lipid metabolism: Immunogold probes for lipoprotein lipase and cholesterol

Blanchette‐Mackie, E. Joan; Nk, Dwyer; La, Amende

doi:10.1002/aja.1001850218

Cited by 30 publications

(11 citation statements)

References 23 publications

(28 reference statements)

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“…With the use of immunogold staining, other studies have also reported that the primary effect of fasting on the distribution of LPL occurred at the surface of endothelial luminal processes. 24,31 Interestingly, enzyme activity in the interstitial fluid of fasted rats remained unchanged and is consistent with the finding that fasting does not influence myocyte LPL activity (N.S. et al, unpublished observations, 1998).…”

Section: Figuresupporting

confidence: 76%

Localization of Lipoprotein Lipase in the Diabetic Heart

Sambandam

Abrahani

Pierre

et al. 1999

ATVB

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Abstract-Vascular endothelium-bound lipoprotein lipase (LPL) is rate limiting for free fatty acid (FFA) transport into tissues. In streptozotocin (STZ)-diabetic rats, we have previously demonstrated an increased heparin-releasable LPL activity from perfused hearts. Because heparin can traverse the endothelial barrier, conventional Langendorff retrograde perfusion of the heart with heparin could release LPL from both the capillary luminal and abluminal surfaces. To determine the precise location of the augmented LPL, a modified Langendorff retrograde perfusion was used to isolate the enzyme at the coronary lumen from that in the interstitial effluent. In response to heparin, a 4-fold increase in LPL activity and protein mass was observed in the coronary perfusate after 2 weeks of STZ diabetes. Release of LPL activity into the interstitial fluid of control hearts was slow but progressive, whereas in diabetic hearts, peak enzyme activity was observed within 1 to 2 minutes after heparin, followed by a gradual decline. Immunohistochemical studies of myocardial sections confirmed that the augmented LPL in diabetic hearts was mainly localized at the capillary endothelium. To study the acute effects of insulin on endothelial LPL activity, we examined rat hearts at various times after the onset of hyperglycemia. An increased heparin-releasable LPL activity in diabetic rats was demonstrated shortly (6 to 24 hours) after STZ injection or after withdrawal from exogenous insulin. Heparin-releasable coronary LPL activity was also increased after an overnight fast. These studies indicate that the intravascular heparin-releasable fraction of cardiac LPL activity is acutely regulated by short-term changes in insulin rather than glucose. Thus, during short periods (hours) of hypoinsulinemia, increased LPL activity at the capillary endothelium can increase the delivery of FFAs to the heart. The resultant metabolic changes could induce the subsequent cardiomyopathy that is observed in the chronic diabetic rat.

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Section: Figuresupporting

confidence: 76%

Localization of Lipoprotein Lipase in the Diabetic Heart

Sambandam

Abrahani

Pierre

et al. 1999

ATVB

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“…LPL synthesized in cardiomyocytes is secreted as an active enzyme and binds to myocyte cell surface heparan sulfate proteoglycans (HSPG). Subsequently, the enzyme is translocated to comparable HSPG binding sites on the luminal side of the vessel wall where TG lipolysis occurs (6,7,38,39).…”

mentioning

confidence: 99%

The metabolic “switch” AMPK regulates cardiac heparin-releasable lipoprotein lipase

Ding¹,

Pulinilkunnil²,

Qi³

et al. 2005

American Journal of Physiology-Endocrinology and Metabolism

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The "fuel gauge" AMP-activated protein kinase (AMPK) facilitates ATP production to meet energy demands during metabolic stress. Given the importance of lipoprotein lipase (LPL) in providing hearts with fatty acids (FA), the preferred substrate consumed by the heart, the objective of the present study was to investigate whether activation of AMPK influences LPL at its functionally relevant location, the coronary lumen. Hearts from overnight-fasted rats were first perfused with heparin to release LPL, and homogenates from these hearts were then used to measure total and phospho-AMPK-alpha by Western blotting. Manipulation of AMPK activity [with drugs like adenine 9-beta-D-arabinofuranoside (Ara-A) and insulin (that inhibit) or perhexiline and oligomycin (that stimulate)] and its influence on LPL was also determined. Fasting augmented the activity of both AMPK and luminal LPL on immediate removal of hearts, effects that still remained even after in vitro perfusion of hearts for 1 h. Inhibition of AMPK in fasted hearts using an inhibitor like Ara-A or through provision of insulin markedly lowered the enhanced luminal LPL activity. In contrast, AMPK activators, like perhexiline and oligomycin, produced a significant elevation in heparin-releasable LPL activity. Thus, with fasting or drugs that influence AMPK, a strong correlation between this metabolic switch and cardiac LPL activity was established. Our data suggest that, in addition to its direct role in promoting FA oxidation, AMPK-mediated recruitment of LPL to the coronary lumen could represent an immediate compensatory response by the heart to guarantee FA supply.

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“…In the heart, this enzyme is produced in cardiomyocytes and subsequently secreted onto heparan sulphate proteoglycan (HSPG) binding sites on the myocyte cell surface (11). From here, LPL is transported onto comparable binding sites on the luminal surface of endothelial cells (3). At the lumen, LPL actively metabolizes the TG core of lipoproteins to FA; these released FA are then transported into the heart for numerous metabolic and structural functions.…”

mentioning

confidence: 99%

Endothelial heparanase secretion after acute hypoinsulinemia is regulated by glucose and fatty acid

Wang

Kim²,

Puthanveetil

et al. 2009

American Journal of Physiology-Heart and Circulatory Physiology

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Following diabetes, the heart increases its lipoprotein lipase (LPL) at the coronary lumen by transferring LPL from the cardiomyocyte to the endothelial lumen. We examined how hyperglycemia controls secretion of heparanase, the enzyme that cleaves myocyte heparan sulphate proteoglycan to initiate this movement. Diazoxide (DZ) was used to decrease serum insulin and generate hyperglycemia. A modified Langendorff technique was used to separate coronary from interstitial effluent, which were assayed for heparanase and LPL. Within 30 min of DZ, interstitial heparanase increased, an effect that closely mirrored an augmentation in interstitial LPL. Endothelial cells were incubated with palmitic acid (PA) or glucose, and heparanase secretion was determined. PA increased intracellular heparanase, with no effect on secretion of this enzyme. Unlike PA, glucose dosedependently lowered endothelial intracellular heparanase, which was strongly associated with increased heparanase activity in the incubation medium. Preincubation with cytochalasin D or nocodazole prevented the high glucose-induced depletion of intracellular heparanase. Our data suggest that following hyperglycemia, translocation of LPL from the cardiomyocyte cell surface to the apical side of endothelial cells is dependent on the ability of the fatty acid to increase endothelial intracellular heparanase followed by rapid secretion of this enzyme by glucose, which requires an intact microtubule and actin cytoskeleton. diabetes; diazoxide; high glucose; endothelial cell; cytoskeleton SINCE UNINTERRUPTED contraction is a unique feature of the heart, cardiac muscle has a high demand for provision of energy (2). Under normal physiological conditions, hearts can utilize multiple substrates, including fatty acid (FA), carbohydrate, amino acid, and ketone bodies. Among these substrates, carbohydrate (ϳ30%) and FA (ϳ70%) are the major sources from which the heart derives most of its energy (29). FA delivery and utilization by the heart involves 1) release from adipose tissue and transport to the heart after complexing with albumin (19), 2) provision through the breakdown of endogenous cardiac triglyceride (TG) stores (23), 3) internalization of whole lipoproteins (14), and 4) hydrolysis of circulating TG-rich lipoproteins (very low density lipoproteins and chylomicrons) to FA by lipoprotein lipase (LPL) positioned at the endothelial surface of the coronary lumen (4). Despite this critical function, coronary endothelial cells do not synthesize LPL (6). In the heart, this enzyme is produced in cardiomyocytes and subsequently secreted onto heparan sulphate proteoglycan (HSPG) binding sites on the myocyte cell surface (11). From here, LPL is transported onto comparable binding sites on the luminal surface of endothelial cells (3). At the lumen, LPL actively metabolizes the TG core of lipoproteins to FA; these released FA are then transported into the heart for numerous metabolic and structural functions.LPL synthesis and activity is regulated in a tissue-specific manner by v...

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Cytochemical studies of lipid metabolism: Immunogold probes for lipoprotein lipase and cholesterol

Cited by 30 publications

References 23 publications

Localization of Lipoprotein Lipase in the Diabetic Heart

Localization of Lipoprotein Lipase in the Diabetic Heart

The metabolic “switch” AMPK regulates cardiac heparin-releasable lipoprotein lipase

Endothelial heparanase secretion after acute hypoinsulinemia is regulated by glucose and fatty acid

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