A major genetic locus in <i>Trypanosoma brucei</i> is a determinant of host pathology

The progression and variation of pathology during infections can be due to components from both host or pathogen, and/or the interaction between them. The influence of host genetic variation on disease pathology during infections with trypanosomes has been well studied in recent years, but the role of parasite genetic variation has not been extensively studied. We have shown that there is parasite strain-specific variation in the level of splenomegaly and hepatomegaly in infected mice and used a forward genetic approach to identify the parasite loci that determine this variation. This approach allowed us to dissect and identify the parasite loci that determine the complex phenotypes induced by infection. Using the available trypanosome genetic map, a major quantitative trait locus (QTL) was identified on T. brucei chromosome 3 (LOD = 7.2) that accounted for approximately two thirds of the variance observed in each of two correlated phenotypes, splenomegaly and hepatomegaly, in the infected mice (named &lt;i&gt;TbOrg1&lt;/i&gt;). In addition, a second locus was identified that contributed to splenomegaly, hepatomegaly and reticulocytosis (&lt;i&gt;TbOrg2&lt;/i&gt;). This is the first use of quantitative trait locus mapping in a diploid protozoan and shows that there are trypanosome genes that directly contribute to the progression of pathology during infections and, therefore, that parasite genetic variation can be a critical factor in disease outcome. The identification of parasite loci is a first step towards identifying the genes that are responsible for these important traits and shows the power of genetic analysis as a tool for dissecting complex quantitative phenotypic traits

Soluble Guanylate Cyclase α1–Deficient Mice: A Novel Murine Model for Primary Open Angle Glaucoma

Primary open angle glaucoma (POAG) is a leading cause of blindness worldwide. The molecular signaling involved in the pathogenesis of POAG remains unknown. Here, we report that mice lacking the $α_1$ subunit of the nitric oxide receptor soluble guanylate cyclase represent a novel and translatable animal model of POAG, characterized by thinning of the retinal nerve fiber layer and loss of optic nerve axons in the context of an open iridocorneal angle. The optic neuropathy associated with soluble guanylate cyclase $α_1$–deficiency was accompanied by modestly increased intraocular pressure and retinal vascular dysfunction. Moreover, data from a candidate gene association study suggests that a variant in the locus containing the genes encoding for the $α_1$ and $β_1$ subunits of soluble guanylate cyclase is associated with POAG in patients presenting with initial paracentral vision loss, a disease subtype thought to be associated with vascular dysregulation. These findings provide new insights into the pathogenesis and genetics of POAG and suggest new therapeutic strategies for POAG

Genetic modifiers of hypertension in soluble guanylate cyclase α1–deficient mice

Nitric oxide (NO) plays an essential role in regulating hypertension and blood flow by inducing relaxation of vascular smooth muscle. Male mice deficient in a NO receptor component, the α1 subunit of soluble guanylate cyclase (sGCα1), are prone to hypertension in some, but not all, mouse strains, suggesting that additional genetic factors contribute to the onset of hypertension. Using linkage analyses, we discovered a quantitative trait locus (QTL) on chromosome 1 that was linked to mean arterial pressure (MAP) in the context of sGCα1 deficiency. This region is syntenic with previously identified blood pressure–related QTLs in the human and rat genome and contains the genes coding for renin. Hypertension was associated with increased activity of the renin-angiotensin-aldosterone system (RAAS). Further, we found that RAAS inhibition normalized MAP and improved endothelium-dependent vasorelaxation in sGCα1-deficient mice. These data identify the RAAS as a blood pressure–modifying mechanism in a setting of impaired NO/cGMP signaling

Nitric oxide synthase 3 deficiency limits adverse ventricular remodeling after pressure overload in insulin resistance

Insulin resistance (IR) and systemic hypertension are independently associated with heart failure. We reported previously that nitric oxide synthase 3 (NOS3) has a beneficial effect on left ventricular (LV) remodeling and function after pressure-overload in mice. The aim of our study was to investigate the interaction of IR and NOS3 in pressure-overload-induced LV remodeling and dysfunction. Wild-type (WT) and NOS3-deficient (NOS3−/−) mice were fed either a standard diet (SD) or a high-fat diet (HFD) to induce IR. After 9 days of diet, mice underwent transverse aortic constriction (TAC). LV structure and function were assessed serially using echocardiography. Cardiomyocytes were isolated, and levels of oxidative stress were evaluated using 2′,7′-dichlorodihydrofluorescein diacetate. Cardiac mitochondria were isolated, and mitochondrial respiration and ATP production were measured. TAC induced LV remodeling and dysfunction in all mice. The TAC-induced decrease in LV function was greater in SD-fed NOS3−/− mice than in SD-fed WT mice. In contrast, HFD-fed NOS3−/− developed less LV remodeling and dysfunction and had better survival than did HFD-fed WT mice. Seven days after TAC, oxidative stress levels were lower in cardiomyocytes from HFD-fed NOS3−/− than in those from HFD-fed WT. Nω-nitro-l-arginine methyl ester and mitochondrial inhibitors (rotenone and 2-thenoyltrifluoroacetone) decreased oxidative stress levels in cardiomyocytes from HFD-fed WT mice. Mitochondrial respiration was altered in NOS3−/− mice but did not worsen after HFD and TAC. In contrast with its protective role in SD, NOS3 increases LV adverse remodeling after pressure overload in HFD-fed, insulin resistant mice. Interactions between NOS3 and mitochondria may be responsible for increased oxidative stress levels in HFD-fed WT mice hearts

Soluble guanylate cyclase-α1 is required for the cardioprotective effects of inhaled nitric oxide

Reperfusion injury limits the benefits of revascularization in the treatment of myocardial infarction (MI). Breathing nitric oxide (NO) reduces cardiac ischemia-reperfusion injury in animal models; however, the signaling pathways by which inhaled NO confers cardioprotection remain uncertain. The objective of this study was to learn whether inhaled NO reduces cardiac ischemia-reperfusion injury by activating the cGMP-generating enzyme, soluble guanylate cyclase (sGC), and to investigate whether bone marrow (BM)-derived cells participate in the sGC-mediated cardioprotective effects of inhaled NO. Wild-type (WT) mice and mice deficient in the sGC α1-subunit (sGCα1−/− mice) were subjected to cardiac ischemia for 1 h, followed by 24 h of reperfusion. During ischemia and for the first 10 min of reperfusion, mice were ventilated with oxygen or with oxygen supplemented with NO (80 parts per million). The ratio of MI size to area at risk (MI/AAR) did not differ in WT and sGCα1−/− mice that did not breathe NO. Breathing NO decreased MI/AAR in WT mice (41%, P = 0.002) but not in sGCα1−/− mice (7%, P = not significant). BM transplantation was performed to restore WT BM-derived cells to sGCα1−/− mice. Breathing NO decreased MI/AAR in sGCα1−/− mice carrying WT BM (39%, P = 0.031). In conclusion, these results demonstrate that a global deficiency of sGCα1 does not alter the degree of cardiac ischemia-reperfusion injury in mice. The cardioprotective effects of inhaled NO require the presence of sGCα1. Moreover, our studies suggest that BM-derived cells are key mediators of the ability of NO to reduce cardiac ischemia-reperfusion injury