Adipose-targeted SWELL1 deletion exacerbates obesity- and age-related nonalcoholic fatty liver disease.

Healthy expansion of adipose tissue is critical for the maintenance of metabolic health, providing an optimized reservoir for energy storage in the form of triacylglycerol-rich lipoproteins. Dysfunctional adipocytes that are unable to efficiently store lipid can result in lipodystrophy and contribute to nonalcoholic fatty liver disease (NAFLD) and metabolic syndrome. Leucine-rich repeat containing protein 8a/SWELL1 functionally encodes the volume-regulated anion channel complex in adipocytes, is induced in early obesity, and is required for normal adipocyte expansion during high-fat feeding. Adipose-specific SWELL1 ablation (Adipo KO) leads to insulin resistance and hyperglycemia during caloric excess, both of which are associated with NAFLD. Here, we show that Adipo-KO mice exhibited impaired adipose depot expansion and excess lipolysis when raised on a variety of high-fat diets, resulting in increased diacylglycerides and hepatic steatosis, thereby driving liver injury. Liver lipidomic analysis revealed increases in oleic acid-containing hepatic triacylglycerides and injurious hepatic diacylglyceride species, with reductions in hepatocyte-protective phospholipids and antiinflammatory free fatty acids. Aged Adipo-KO mice developed hepatic steatosis on a regular chow diet, and Adipo-KO male mice developed spontaneous, aggressive hepatocellular carcinomas (HCCs). These data highlight the importance of adipocyte SWELL1 for healthy adipocyte expansion to protect against NAFLD and HCC in the setting of overnutrition and with aging.

Small molecule SWELL1 complex induction improves glycemic control and nonalcoholic fatty liver disease in murine Type 2 diabetes.

Type 2 diabetes is associated with insulin resistance, impaired pancreatic ß-cell insulin secretion, and nonalcoholic fatty liver disease. Tissue-specific SWELL1 ablation impairs insulin signaling in adipose, skeletal muscle, and endothelium, and impairs ß-cell insulin secretion and glycemic control. Here, we show that ICl,SWELL and SWELL1 protein are reduced in adipose and ß-cells in murine and human diabetes. Combining cryo-electron microscopy, molecular docking, medicinal chemistry, and functional studies, we define a structure activity relationship to rationally-design active derivatives of a SWELL1 channel inhibitor (DCPIB/SN-401), that bind the SWELL1 hexameric complex, restore SWELL1 protein, plasma membrane trafficking, signaling, glycemic control and islet insulin secretion via SWELL1-dependent mechanisms. In vivo, SN-401 restores glycemic control, reduces hepatic steatosis/injury, improves insulin-sensitivity and insulin secretion in murine diabetes. These findings demonstrate that SWELL1 channel modulators improve SWELL1-dependent systemic metabolism in Type 2 diabetes, representing a first-in-class therapeutic approach for diabetes and nonalcoholic fatty liver disease.

The SWELL1-LRRC8 complex regulates endothelial AKT-eNOS signaling and vascular function.

The endothelium responds to numerous chemical and mechanical factors in regulating vascular tone, blood pressure, and blood flow. The endothelial volume-regulated anion channel (VRAC) has been proposed to be mechanosensitive and thereby sense fluid flow and hydrostatic pressure to regulate vascular function. Here, we show that the leucine-rich repeat-containing protein 8a, LRRC8A (SWELL1), is required for VRAC in human umbilical vein endothelial cells (HUVECs). Endothelial LRRC8A regulates AKT-endothelial nitric oxide synthase (eNOS) signaling under basal, stretch, and shear-flow stimulation, forms a GRB2-Cav1-eNOS signaling complex, and is required for endothelial cell alignment to laminar shear flow. Endothelium-restricted Lrrc8a KO mice develop hypertension in response to chronic angiotensin-II infusion and exhibit impaired retinal blood flow with both diffuse and focal blood vessel narrowing in the setting of type 2 diabetes (T2D). These data demonstrate that LRRC8A regulates AKT-eNOS in endothelium and is required for maintaining vascular function, particularly in the setting of T2D.

SWELL1 regulates skeletal muscle cell size, intracellular signaling, adiposity and glucose metabolism.

Maintenance of skeletal muscle is beneficial in obesity and Type 2 diabetes. Mechanical stimulation can regulate skeletal muscle differentiation, growth and metabolism; however, the molecular mechanosensor remains unknown. Here, we show that SWELL1 (Lrrc8a) functionally encodes a swell-activated anion channel that regulates PI3K-AKT, ERK1/2, mTOR signaling, muscle differentiation, myoblast fusion, cellular oxygen consumption, and glycolysis in skeletal muscle cells. LRRC8A over-expression in Lrrc8a KO myotubes boosts PI3K-AKT-mTOR signaling to supra-normal levels and fully rescues myotube formation. Skeletal muscle-targeted Lrrc8a KO mice have smaller myofibers, generate less force ex vivo, and exhibit reduced exercise endurance, associated with increased adiposity under basal conditions, and glucose intolerance and insulin resistance when raised on a high-fat diet, compared to wild-type (WT) mice. These results reveal that the LRRC8 complex regulates insulin-PI3K-AKT-mTOR signaling in skeletal muscle to influence skeletal muscle differentiation in vitro and skeletal myofiber size, muscle function, adiposity and systemic metabolism in vivo.

Skeletal muscles ­ the force-generating tissue attached to bones ­ must maintain their mass and health for the body to work properly. It is therefore necessary to understand how an organism can regulate the way skeletal muscles form, grow and heal. A multitude of factors can control how muscles form, including mechanical signals. The molecules that can sense these mechanical stimuli, however, remain unknown. Mechanoresponsive ion channels provide possible candidates for these molecular sensors. These proteins are studded through the cell membranes, where they can respond to mechanical changes by opening and allowing the flow of ions in and out of a cell, or by changing interactions with other proteins. The SWELL1 protein is a component of an ion channel known as VRAC, which potentially responds to mechanical stimuli. This channel is associated with many biological processes such as cells multiplying, migrating, growing and dying, but it is still unclear how. Here, Kumar et al. first tested whether SWELL1 controls how skeletal muscle precursors mature into their differentiated and functional form. These experiments showed that SWELL1 regulates this differentiation process under the influence of the hormone insulin, as well as mechanical signals such as cell stretching. In addition, this work revealed that SWELL1 relies on an adaptor molecule called GRB2 to relay these signals in the cell. Next, Kumar et al. genetically engineered mice lacking SWELL1 only in skeletal muscle. These animals had smaller muscle cells, as well as muscles that were weaker and less enduring. When raised on a high-calorie diet, the mutant mice also got more obese and developed resistance to insulin, which is an important step driving obesity-induced diabetes. Together, these findings show that SWELL1 helps to regulate the formation and function of muscle cells, and highlights how an ion channel participates in these processes. Healthy muscles are key for overall wellbeing, as they also protect against obesity and obesity-related conditions such as type 2 diabetes or nonalcoholic fatty liver disease. This suggests that targeting SWELL1 could prove advantageous in a clinical setting.

SWELL signalling in adipocytes: can fat 'feel' fat?

Obesity is becoming a global epidemic, predisposing to Type 2 diabetes, cardiovascular disease, fatty liver disease, pulmonary disease, osteoarthritis and cancer. Therefore, understanding the biology of adipocyte expansion in response to overnutrition is critical to devising strategies to treat obesity, and the associated burden of morbidity and mortality. Through exploratory patch-clamp experiments in freshly isolated primary murine and human adipocytes, we recently determined that SWELL1/LRRC8a, a leucine-rich repeat containing transmembrane protein, functionally encoded an ion channel signalling complex (the volume-regulated anion channel, or VRAC) on the adipocyte plasma membrane. The SWELL1-/LRRC8 channel complex activates in response to increases in adipocyte volume and in the context of obesity. SWELL1 is also required for insulin-PI3K-AKT2 signalling to regulate adipocyte growth and systemic glycaemia. This commentary delves further into our working models for the molecular mechanisms of adipocyte SWELL1-mediated VRAC activation, proposed signal transduction mechanisms, and putative impact on adipocyte hypertrophy during caloric excess.

Defective protein repair under methionine sulfoxide A deletion drives autophagy and ARE-dependent gene transcription.

OBJECTIVE: Reduction of oxidized methionines is emerging as a major protein repair pathway. The lack of methionine sulfoxide reductase A (MsrA) exacerbates cardiovascular disease phenotypes driven by increased oxidative stress. However, the role of MsrA on maintaining cellular homeostasis in the absence of excessive oxidative stress is less well understood. METHODS AND RESULTS: Constitutive genetic deletion of MsrA increased formation of p62-containing protein aggregates, activated autophagy, and decreased a marker of apoptosis in vascular smooth muscle cells (VSMC). The association of Keap1 with p62 was augmented in MsrA-/- VSMC. Keap1 targets the transcription factor Nrf2, which regulates antioxidant genes, for proteasomal degradation. However, in MsrA-/- VSMC, the association of Nrf2 with Keap1 was diminished. Whereas Nrf2 mRNA levels were not decreased in MsrA-/- VSMC, we detected decreased ubiquitination of Nrf2 and a corresponding increase in total Nrf2 protein in the absence of biochemical markers of oxidative stress. Moreover, nuclear-localized Nrf2 was increased under MsrA deficiency, resulting in upregulation of Nrf2-dependent transcriptional activity. Consequently, transcription, protein levels and enzymatic activity of glutamate-cysteine ligase and glutathione reductase were greatly augmented in MsrA-/- VSMC. SUMMARY: Our findings demonstrate that reversal of methionine oxidation is required for maintenance of cellular homeostasis in the absence of increased oxidative stress. These data provide the first link between autophagy and activation of Nrf2 in the setting of MsrA deletion.

SWELL1 is a glucose sensor regulating ß-cell excitability and systemic glycaemia.

Insulin secretion is initiated by activation of voltage-gated Ca2+ channels (VGCC) to trigger Ca2+-mediated insulin vesicle fusion with the ß-cell plasma membrane. The firing of VGCC requires ß-cell membrane depolarization, which is regulated by a balance of depolarizing and hyperpolarizing ionic currents. Here, we show that SWELL1 mediates a swell-activated, depolarizing chloride current (ICl,SWELL) in both murine and human ß-cells. Hypotonic and glucose-stimulated ß-cell swelling activates SWELL1-mediated ICl,SWELL and this contributes to membrane depolarization and activation of VGCC-dependent intracellular calcium signaling. SWELL1 depletion in MIN6 cells and islets significantly impairs glucose-stimulated insulin secretion. Tamoxifen-inducible ß-cell-targeted Swell1 KO mice have normal fasting serum glucose and insulin levels but impaired glucose-stimulated insulin secretion and glucose tolerance; and this is further exacerbated in mild obesity. Our results reveal that ß-cell SWELL1 modulates insulin secretion and systemic glycaemia by linking glucose-mediated ß-cell swelling to membrane depolarization and activation of VGCC-triggered calcium signaling.

Induction of adipose and hepatic SWELL1 expression is required for maintaining systemic insulin-sensitivity in obesity.

Obesity is associated with a loss of insulin-sensitivity and systemic dysglycemia, resulting in Type 2 diabetes, however the molecular mechanisms underlying this association are unclear. Through adipocyte patch-clamp studies, we recently showed that SWELL1 is required for the Volume-Regulated Anion Current (VRAC) in adipocytes and that SWELL1-mediated VRAC is activated by both mechanical and pathophysiological adipocyte expansion. We also demonstrated that adipocyte SWELL1 is required for maintaining insulin signaling and glucose homeostasis, particularly in the setting of obesity. Here we show that SWELL1 protein expression is induced in subcutaneous fat, visceral fat and liver in the setting of obesity. Long- term AAV/rec2-shRNA mediated SWELL1 knock-down in both fat and liver are associated with increased weight gain, increased adiposity and exacerbated insulin resistance in mice raised on a high-fat diet. These data further support the notion that SWELL1 induction occurs in insulin- sensitive tissues (liver and adipose) in the setting of over-nutrition and contributes to improved systemic glycemia by supporting enhanced insulin-sensitivity.

Erratum: SWELL1 is a regulator of adipocyte size, insulin signalling and glucose homeostasis.

This corrects the article DOI: 10.1038/ncb3514.

SWELL1 is a regulator of adipocyte size, insulin signalling and glucose homeostasis.

Adipocytes undergo considerable volumetric expansion in the setting of obesity. It has been proposed that such marked increases in adipocyte size may be sensed via adipocyte-autonomous mechanisms to mediate size-dependent intracellular signalling. Here, we show that SWELL1 (LRRC8a), a member of the Leucine-Rich Repeat Containing protein family, is an essential component of a volume-sensitive ion channel (VRAC) in adipocytes. We find that SWELL1-mediated VRAC is augmented in hypertrophic murine and human adipocytes in the setting of obesity. SWELL1 regulates adipocyte insulin-PI3K-AKT2-GLUT4 signalling, glucose uptake and lipid content via SWELL1 C-terminal leucine-rich repeat domain interactions with GRB2/Cav1. Silencing GRB2 in SWELL1 KO adipocytes rescues insulin-pAKT2 signalling. In vivo, shRNA-mediated SWELL1 knockdown and adipose-targeted SWELL1 knockout reduce adiposity and adipocyte size in obese mice while impairing systemic glycaemia and insulin sensitivity. These studies identify SWELL1 as a cell-autonomous sensor of adipocyte size that regulates adipocyte growth, insulin sensitivity and glucose tolerance.

Isolation and Patch-Clamp of Primary Adipocytes.

The patch-clamp technique allows for the study of ion channel activity in the native adipocyte environment to better understand the contributions of ion channels to adipocyte signaling. Here, we describe methods for isolating primary mature adipocytes from both mouse and human white adipose tissues (subcutaneous and visceral). From the same preparation, we describe how to culture and differentiate preadipocytes isolated from the stromal vascular fraction. We then describe in detail patch-clamp methods, including both whole-cell and perforated-patch configurations.

Deletion of Methionine Sulfoxide Reductase A Does Not Affect Atherothrombosis but Promotes Neointimal Hyperplasia and Extracellular Signal-Regulated Kinase 1/2 Signaling.

OBJECTIVE: Emerging evidence suggests that methionine oxidation can directly affect protein function and may be linked to cardiovascular disease. The objective of this study was to define the role of the methionine sulfoxide reductase A (MsrA) in models of vascular disease and identify its signaling pathways. APPROACH AND RESULTS: MsrA was readily identified in all layers of the vascular wall in human and murine arteries. Deletion of the MsrA gene did not affect atherosclerotic lesion area in apolipoprotein E-deficient mice and had no significant effect on susceptibility to experimental thrombosis after photochemical injury. In contrast, the neointimal area after vascular injury caused by complete ligation of the common carotid artery was significantly greater in MsrA-deficient than in control mice. In aortic vascular smooth muscle cells lacking MsrA, cell proliferation was significantly increased because of accelerated G1/S transition. In parallel, cyclin D1 protein and cdk4/cyclin D1 complex formation and activity were increased in MsrA-deficient vascular smooth muscle cell, leading to enhanced retinoblastoma protein phosphorylation and transcription of E2F. Finally, MsrA-deficient vascular smooth muscle cell exhibited greater activation of extracellular signal-regulated kinase 1/2 that was caused by increased activity of the Ras/Raf/mitogen-activated protein kinase signaling pathway. CONCLUSIONS: Our findings implicate MsrA as a negative regulator of vascular smooth muscle cell proliferation and neointimal hyperplasia after vascular injury through control of the Ras/Raf/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase 1/2 signaling pathway.

Oxidative activation of the Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) regulates vascular smooth muscle migration and apoptosis.

Activation of the Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and reactive oxygen species (ROS) promote neointimal hyperplasia after vascular injury. CaMKII can be directly activated by ROS through oxidation. In this study, we determined whether abolishing the oxidative activation site of CaMKII alters vascular smooth muscle cell (VCMC) proliferation, migration and apoptosis in vitro and neointimal formation in vivo. VSMC isolated from a knock-in mouse with oxidation-resistant CaMKIIδ (CaMKII M2V) displayed similar proliferation but decreased migration and apoptosis. Surprisingly, ROS production and expression of the NADPH oxidase subunits p47 and p22 were decreased in M2V VSMC, whereas superoxide dismutase 2 protein expression was upregulated. In vivo, after carotid artery ligation, no differences in neointimal size or remodeling were observed. In contrast to VSMC, CaMKII expression and autonomous activity were significantly higher in M2V compared to WT carotid arteries, suggesting that an autoregulatory mechanism determines CaMKII activity in vivo. Our findings demonstrate that preventing oxidative activation of CaMKII decreases migration and apoptosis in vitro and suggest that CaMKII regulates ROS production. Our study presents novel evidence that CaMKII expression in vivo is regulated by a negative feedback loop following oxidative activation.

The multifunctional Ca²âº/calmodulin-dependent kinase IIδ (CaMKIIδ) regulates arteriogenesis in a mouse model of flow-mediated remodeling.

OBJECTIVE: Sustained hemodynamic stress mediated by high blood flow promotes arteriogenesis, the outward remodeling of existing arteries. Here, we examined whether Ca²âº/calmodulin-dependent kinase II (CaMKII) regulates arteriogenesis. METHODS AND RESULTS: Ligation of the left common carotid led to an increase in vessel diameter and perimeter of internal and external elastic lamina in the contralateral, right common carotid. Deletion of CaMKIIδ (CaMKIIδ-/-) abolished this outward remodeling. Carotid ligation increased CaMKII expression and was associated with oxidative activation of CaMKII in the adventitia and endothelium. Remodeling was abrogated in a knock-in model in which oxidative activation of CaMKII is abolished. Early after ligation, matrix metalloproteinase 9 (MMP9) was robustly expressed in the adventitia of right carotid arteries of WT but not CaMKIIδ-/- mice. MMP9 mainly colocalized with adventitial macrophages. In contrast, we did not observe an effect of CaMKIIδ deficiency on other proposed mediators of arteriogenesis such as expression of adhesion molecules or smooth muscle proliferation. Transplantation of WT bone marrow into CaMKIIδ-/- mice normalized flow-mediated remodeling. CONCLUSION: CaMKIIδ is activated by oxidation under high blood flow conditions and is required for flow-mediated remodeling through a mechanism that includes increased MMP9 expression in bone marrow-derived cells invading the arterial wall.

The multifunctional Ca2+/calmodulin-dependent kinase II regulates vascular smooth muscle migration through matrix metalloproteinase 9.

The multifunctional CaMKII has been implicated in vascular smooth muscle cell (VSMC) migration, but little is known regarding its downstream targets that mediate migration. Here, we examined whether CaMKII regulates migration through modulation of matrix metalloproteinase 9 (MMP9). Using CaMKIIδ(-/-) mice as a model system, we evaluated migration and MMP9 regulation in vitro and in vivo. After ligation of the common carotid artery, CaMKII was activated in the neointima as determined by oxidation and autophosphorylation. We found that MMP9 was robustly expressed in the neointima and adventitia of carotid-ligated wild-type (WT) mice but was barely detectable in CaMKIIδ(-/-) mice. The perimeter of the external elastic lamina, a correlate of migration-related outward remodeling, was increased in WT but not in CaMKIIδ(-/-) mice. Migration induced by serum, platelet-derived growth factor, and tumor necrosis factor-α (TNF-α) was significantly decreased in CaMKIIδ(-/-) as compared with WT VSMCs, but migration was rescued with adenoviral overexpression of MMP9 in CaMKIIδ(-/-) VSMCs. Likewise, overexpression of CaMKIIδ in CaMKIIδ(-/-) VSMCs increased migration, whereas an oxidation-resistant mutant of CaMKIIδ did not. TNF-α strongly induced CaMKII oxidation and autophosphorylation as well as MMP9 activity, mRNA, and protein levels in WT, but not in CaMKIIδ(-/-) VSMC. Surprisingly, TNF-α strongly induced MMP9 promoter activity in WT and CaMKIIδ(-/-) VSMC. However, the MMP9 mRNA stability was significantly decreased in CaMKIIδ(-/-) VSMC. Our data demonstrate that CaMKII promotes VSMC migration through posttranscriptional regulation of MMP9 and suggest that CaMKII effects on MMP9 expression may be a therapeutic pathway in vascular injury.

Altering α-dystroglycan receptor affinity of LCMV pseudotyped lentivirus yields unique cell and tissue tropism.

BACKGROUND: The envelope glycoprotein of lymphocytic choriomeningitis virus (LCMV) can efficiently pseudotype lentiviral vectors. Some strains of LCMV exploit high affinity interactions with α-dystroglycan (α-DG) to bind to cell surfaces and subsequently fuse in low pH endosomes. LCMV strains with low α-DG affinity utilize an unknown receptor and display unique tissue tropisms. We pseudotyped non-primate feline immunodeficiency virus (FIV) vectors using LCMV derived glycoproteins with high or low affinity to α-DG and evaluated their properties in vitro and in vivo. METHODS: We pseudotyped FIV with the LCMV WE54 strain envelope glycoprotein and also engineered a point mutation in the WE54 envelope glycoprotein (L260F) to diminish α-DG affinity and direct binding to alternate receptors. We hypothesized that this change would alter in vivo tissue tropism and enhance gene transfer to neonatal animals. RESULTS: In mice, hepatic α- and ß-DG expression was greatest at the late gestational and neonatal time points. When displayed on the surface of the FIV lentivirus the WE54 L260F mutant glycoprotein bound weakly to immobilized α-DG. Additionally, LCMV WE54 pseudotyped FIV vector transduction was neutralized by pre-incubation with soluble α-DG, while the mutant glycoprotein pseudotyped vector was not. In vivo gene transfer in adult mice with either envelope yielded low transduction efficiencies in hepatocytes following intravenous delivery. In marked contrast, neonatal gene transfer with the LCMV envelopes, and notably with the FIV-L260F vector, conferred abundant liver and lower level cardiomyocyte transduction as detected by luciferase assays, bioluminescent imaging, and ß-galactosidase staining. CONCLUSIONS: These results suggest that a developmentally regulated receptor for LCMV is expressed abundantly in neonatal mice. LCMV pseudotyped vectors may have applications for neonatal gene transfer. ABBREVIATIONS: Armstrong 53b (Arm53b); baculovirus Autographa californica GP64 (GP64); charge-coupled device (CCD); dystroglycan (DG); feline immunodeficiency virus (FIV); glycoprotein precursor (GP-C); firefly luciferase (Luc); lymphocytic choriomeningitis virus (LCMV); nuclear targeted ß-galactosidase (ntLacZ); optical density (OD); PBS/0.1% (w/v) Tween-20 (PBST); relative light units (RLU); Rous sarcoma virus (RSV); transducing units per milliliter (TU/ml); vesicular stomatitis virus (VSV-G); wheat germ agglutinin (WGA); 50% reduction in binding (C50).

Integration site choice of a feline immunodeficiency virus vector.

We mapped 226 unique integration sites in human hepatoma cells following gene transfer with a feline immunodeficiency virus (FIV)-based lentivirus vector. FIV integrated across the entire length of the transcriptional units. Microarray data indicated that FIV integration favored actively transcribed genes. Approximately 21% of FIV integrations within transcriptional units occurred in genes regulated by the LEDGF/p75 transcriptional coactivator. DNA in regions of FIV insertion sites exhibited a "bendable" structure and a pattern of duplex destabilization favoring strand separation. FIV integration preferences are more similar to those of primate lentiviruses and distinct from those of Moloney murine leukemia virus, avian sarcoma leukosis virus, and foamy virus.

Persistent expression of factor VIII in vivo following nonprimate lentiviral gene transfer.

Hemophilia A is a clinically important coagulation disorder caused by the lack or abnormality of plasma coagulation factor VIII (FVIII). Gene transfer of the FVIII cDNA to hepatocytes using lentiviral vectors is a potential therapeutic approach. We investigated the efficacy of feline immunodeficiency virus (FIV)-based vectors in targeting hepatocytes and correcting FVIII deficiency in a hemophilia A mouse model. Several viral envelope glycoproteins were screened for efficient FIV vector pseudotyping and hepatocyte transduction. The GP64 glycoprotein from baculovirus Autographa californica multinuclear polyhedrosis virus pseudo-typed FIV efficiently and showed excellent hepatocyte tropism. The GP64-pseudotyped vector was stable in the presence of human or mouse complement. Inclusion of a hybrid liver-specific promoter (murine albumin enhancer/human alpha1-antitrypsin promoter) further enhanced transgene expression in hepatocytes. We generated a GP64-pseudotyped FIV vector encoding the B domain-deleted human FVIII coding region driven by the liver-specific promoter, with 2 beneficial point mutations in the A1 domain. Intravenous vector administration conferred sustained FVIII expression in hemophilia A mice for several months without the generation of anti-human FVIII antibodies and resulted in partial phenotypic correction. These findings demonstrate the utility of GP64-pseudotyped FIV lentiviral vectors for targeting hepatocytes to correct disorders associated with deficiencies of secreted proteins.

Heat-induced liver injury in old rats is associated with exaggerated oxidative stress and altered transcription factor activation.

A decline in stress tolerance is a hallmark of aging. For instance, older organisms showed extensive hepatic damage, along with increased morbidity and mortality, after environmental heating. We hypothesized that hyperthermic challenge would produce exaggerated oxidative stress in old animals, leading to increased hepatic injury. After a heat-stress protocol, time-course changes in reactive oxygen species (ROS) levels, oxidative damage markers, glutathione (GSH)/glutathione disulfide (GSSG) ratios, and activation of stress-response transcription factors (AP-1 and NF-kappaB) were measured in young and old rats. A small, transient increase in hepatic oxidative damage, with minimal injury, was observed in young rats. However, old rats showed widespread hepatic injury that was manifested over a 24 h period after heating. This pathology was preceded by elevated steady-state levels of ROS, along with large increases in lipid peroxidation products, prolonged hepatic DNA oxidation damage, aberrant GSH/GSSG profiles, and altered activation patterns for AP-1. These data indicate that young animals have an effective oxidation-reduction buffering system in the liver that provides protection from oxidative damage to intracellular macromolecules under stress conditions. In sharp contrast, an environmental challenge in older animals produces exaggerated oxidative stress and alterations in signal transduction pathways, which can contribute to cellular dysfunction and age-related reductions in stress tolerance.