Slc4a11 KO mice also exhibit renal abnormalities, including polyuria with low urine osmolality.
10,11 SLC4A11 is highly expressed in the proximal tubule,
7,10 where numerous mitochondria are present and adenosine triphosphate (ATP) production relies on mitochondrial oxidative phosphorylation fueled mainly by Gln and free fatty acids.
49 We first examined the weight and size of kidneys as this is often a potential surrogate measure of dysfunction. We observed that the kidney to body weight ratio was reduced in
Slc4a11 KO mice at 8-week-old relative to
Slc4a11 WT mice, in both male and female mice (
Figs. 5a,
5b). However, we did not find histomorphologic differences within the renal tissue structure by hematoxylin and eosin staining (data not shown). To determine if Slc4a11 expression facilitates Gln catabolism in the kidney, we examined oxygen consumption of kidney mitochondria isolated from WT and KO mice.
Figure 5c shows that basal oxygen consumption of WT and KO mitochondria was similar in the absence of Gln. However, in the presence of Gln, oxygen consumption increased significantly more in WT. Moreover, calculated proton leak (
Fig. 5d) was increased by Gln in WT but not KO, consistent with a previous study showing NH
3-sensitive mitochondrial uncoupling by Slc4a11.
14 Immunoblotting analysis of mitochondrial and supernatant fractions from
Slc4a11 WT kidneys (
Fig. 5e) revealed that Slc4a11 was markedly enriched in mitochondria (
Fig. 5f). To examine carrier-mediated targeting, kidneys were preconditioned with 20 mg/kg novobiocin, and mitochondrial and supernatant fractions were analyzed by immunoblotting.
Figure 5f shows significant reduction of Slc4a11 and ANT but not RISP expression in the mitochondrial fraction with novobiocin treatment (
Figs. 5f,
5g). In sum, our data show that Slc4a11 is present in kidney mitochondria and HSP90 is necessary for trafficking to the mitochondria. Furthermore, Slc4a11 in the kidneys facilitates Gln catabolism and provides mitochondrial uncoupling.