rAAV9 combined with renal vein injection is optimal for kidney-targeted gene delivery: conclusion of a comparative study

Recent development and gene therapy for glycogen storage disease type Ia

Glycogen storage disease type Ia (GSD-Ia) is an autosomal recessive metabolic disorder caused by a deficiency in glucose-6-phosphatase-α (G6Pase-α or G6PC) that is expressed primarily in the liver, kidney, and intestine. G6Pase-α catalyzes the hydrolysis of glucose-6-phosphate (G6P) to glucose and phosphate in the terminal step of gluconeogenesis and glycogenolysis, and is a key enzyme for endogenous glucose production. The active site of G6Pase-α is inside the endoplasmic reticulum (ER) lumen. For catalysis, the substrate G6P must be translocated from the cytoplasm into the ER lumen by a G6P transporter (G6PT). The functional coupling of G6Pase-α and G6PT maintains interprandial glucose homeostasis. Dietary therapies for GSD-Ia are available, but cannot prevent the long-term complication of hepatocellular adenoma that may undergo malignant transformation to hepatocellular carcinoma. Animal models of GSD-Ia are now available and are being exploited to both delineate the disease more precisely and develop new treatment approaches, including gene therapy.

Intravital imaging of the kidney

Two-photon intravital microscopy is a powerful tool that allows the examination of dynamic cellular processes in the live animal with unprecedented resolution. Indeed, it offers the ability to address unique biological questions that may not be solved by other means. While two-photon intravital microscopy has been successfully applied to study many organs, the kidney presents its own unique challenges that need to be overcome in order to optimize and validate imaging data. For kidney imaging, the complexity of renal architecture and salient autofluorescence merit special considerations as these elements directly impact image acquisition and data interpretation. Here, using illustrative cases, we provide practical guides and discuss issues that may arise during two-photon live imaging of the rodent kidney.

Type I glycogen storage diseases: disorders of the glucose-6-phosphatase/glucose-6-phosphate transporter complexes

Disorders of the glucose-6-phosphatase (G6Pase)/glucose-6-phosphate transporter (G6PT) complexes consist of three subtypes: glycogen storage disease type Ia (GSD-Ia), deficient in the liver/kidney/intestine-restricted G6Pase-α (or G6PC); GSD-Ib, deficient in a ubiquitously expressed G6PT (or SLC37A4); and G6Pase-β deficiency or severe congenital neutropenia syndrome type 4 (SCN4), deficient in the ubiquitously expressed G6Pase-β (or G6PC3). G6Pase-α and G6Pase-β are glucose-6-phosphate (G6P) hydrolases with active sites lying inside the endoplasmic reticulum (ER) lumen and as such are dependent upon the G6PT to translocate G6P from the cytoplasm into the lumen. The tissue expression profiles of the G6Pase enzymes dictate the disease's phenotype. A functional G6Pase-α/G6PT complex maintains interprandial glucose homeostasis, while a functional G6Pase-β/G6PT complex maintains neutrophil/macrophage energy homeostasis and functionality. G6Pase-β deficiency is not a glycogen storage disease but biochemically it is a GSD-I related syndrome (GSD-Irs). GSD-Ia and GSD-Ib patients manifest a common metabolic phenotype of impaired blood glucose homeostasis not shared by GSD-Irs. GSD-Ib and GSD-Irs patients manifest a common myeloid phenotype of neutropenia and neutrophil/macrophage dysfunction not shared by GSD-Ia. While a disruption of the activity of the G6Pase-α/G6PT complex readily explains why GSD-Ia and GSD-Ib patients exhibit impaired glucose homeostasis, the basis for neutropenia and myeloid dysfunction in GSD-Ib and GSD-Irs are only now starting to be understood. Animal models of all three disorders are now available and are being exploited to both delineate the disease more precisely and develop new treatment approaches, including gene therapy.