Knockout of Na-glucose-cotransporter SGLT1 mitigates diabetes-induced upregulation of nitric oxide synthase-1 in macula densa and glomerular hyperfiltration

Abstract

The Na-glucose-cotransporter SGLT1 mediates glucose reabsorption in late proximal tubules. SGLT1 also mediates macula densa-sensing of an increase in luminal glucose, which increases nitric oxide synthase-1 (MD-NOS1)-mediated NO formation and potentially GFR. Here the contribution of SGLT1 was tested by gene-knockout (-/-) in type 1 diabetic Akita mice. A low-glucose diet was fed to prevent intestinal malabsorption in Sglt1-/- mice and minimize the contribution of intestinal SGLT1. Hyperglycemia was modestly reduced in Sglt1-/- vs littermate wild-type (WT) Akita mice (480 vs. 550mg/dl), associated with reduced diabetes-induced increases in GFR, kidney weight, glomerular size, and albuminuria. Blunted hyperfiltration was confirmed in streptozotocin-induced diabetic Sglt1-/- mice, associated with similar hyperglycemia vs WT mice (350 vs. 385mg/dl). Absence of SGLT1 attenuated upregulation of MD-NOS1 protein expression in diabetic Akita mice and in response to SGLT2 inhibition in non-diabetic mice. During SGLT2 inhibition in Akita mice, Sglt1-/- likewise reduced blood glucose (200 vs. 300mg/dl), associated with lesser MD-NOS1 expression, GFR, kidney weight, glomerular size, and albuminuria. Absence of Sglt1 in Akita mice increased systolic blood pressure associated with suppressed renal renin mRNA expression. This may reflect fluid retention due to blunted hyperfiltration. SGLT2 inhibition prevented the blood pressure increase in Sglt1-/- Akita, possibly due to additive glucosuric/diuretic effects. The data indicate that SGLT1 contributes to diabetic hyperfiltration and limits diabetic hypertension. Potential mechanisms include its role in glucose-driven upregulation of MD-NOS1 expression. This pathway may increase GFR to maintain volume balance when enhanced MD glucose delivery indicates upstream saturation of sodium-glucose-cotransporters and thus hyperreabsorption.