Fig 2: Relative protein expression of (A) monocarboxylate transporter (MCT)-1 and (B) MCT2 in mouse tissues in response to fasting and PPARα.Values represent means ± SD of relative protein expression of wildtype (WT) and PPARα knockout (KO) mice that were fed ad libitum or fasted for 48 h (n = 16). Data were analyzed by two-way ANOVA. Classification factors were genotype, fasting, and the interaction between both factors. P-values revealed by two-way ANOVA are noted above the figures. Individual means of the treatment groups were compared by Tukey's test in case of variance homogeneity. In case of variance heterogeneity, as revealed by Levene's test, individual means were compared by Games Howell test. Horizontal brackets represent differences between groups in post-hoc comparison (*p<0.05).

Fig 3: Lack of Slc4a11 leads to increased proton motive force, resulting in increased mitoROS. ROS directly activate Src kinase, phosphorylating tyrosine residues of tight and adherens junction proteins and leading to their degradation and/or mis-localization. Cortical cytoskeleton alterations are induced as a secondary response. The result is perturbation of the barrier function. ROS and Src kinase activation also lead to downregulation of MCT2 and MCT4, as well as decreased Na+-K+-ATPase activity with subsequent stromal lactate accumulation, resulting in failure of the corneal endothelial pump. The end result is corneal edema.

Fig 4: Cx43 is uncoupled from ependymal cells under hyperglycemic conditions; however, GLUT1 and MCT2 do not change the distribution.(A) Immunohistochemical staining of acetylated α-tubulin (green) and Cx43 (red) in frontal brain sections from normoglycemic animals. Staining of the dorsal area of the third ventricle was performed. Scale bar: 20 μm. (B) Immunohistochemical staining of acetylated α-tubulin (green) and Cx43 (red) in frontal brain sections from 5 mM glucose in CSF hyperglycemic animals. Scale bar: 20 μm. (C) Immunohistochemical staining of acetylated α-tubulin (green) and Cx43 (red) in frontal brain sections from 10 mM glucose in CSF hyperglycemic animals. Scale bar: 20 μm. (D) Volume of positive Cx43 particles. The graph shows data from 3 biologically independent samples. The error bars represent the SD; ***P < 0.001 (one-way ANOVA). (E) Size of Cx43 particles. The graph shows data from 3 biologically independent samples. The error bars represent the SD; *P < 0.05 (one-way ANOVA). (F) Integrated fluorescence intensity of Cx43-positive particles. The graph shows data from 3 biologically independent samples. The error bars represent the SD; *P < 0.05, **P < 0.01 (one-way ANOVA). (G-I) TEM of ependymal cells from the brains of normoglycemic or hyperglycemic animals. Spaces were observed between the lateral membranes of ependymal cells under hyperglycemic conditions (yellow arrows). Scale bar: 2 μm. The nucleus of each cell is marked in green. (J-L) Immunohistochemical staining of GLUT1 (red) in frontal brain sections containing SCO cells and ependymal cells (yellow arrows) from normoglycemic and hyperglycemic rats. No changes in distribution were detected under different glycemic conditions. The blood vessels were highly positive (white arrows). N = 3. Scale bar: 30 μm. (M-O) Immunohistochemical staining of MCT2 (green) and SCO-spondin (red) in frontal brain sections containing SCO and ependymal cells (yellow arrows) from normoglycemic and hyperglycemic rats. No changes in distribution were detected under different glycemic conditions. SCO cells did not express MCT2. Ependymal cells and blood vessels (white arrows) were highly positive. N = 3. Scale bar: 20 μm. Data used to generate graphs can be found in S1 Data. BV, blood vessel; CSF, cerebrospinal fluid; Cx43, connexin-43; d3v, dorsal third ventricle; SCO, subcommissural organ; TEM, transmission electron microscopy.

Fig 5: Relative mRNA concentrations of (A) monocarboxylate transporter (MCT)-1, (B) MCT2 and (C) MCT4 in mouse tissues in response to fasting and PPARα.Values represent means ± SD of relative mRNA concentrations of wildtype (WT) and PPARα knockout (KO) mice that were fed ad libitum or fasted for 48 h (n = 16). Data were analyzed by two-way ANOVA. Classification factors were genotype, fasting, and the interaction between both factors. P-values revealed by two-way ANOVA are noted above the figures. Individual means of the treatment groups were compared by Tukey's test in case of variance homogeneity. In case of variance heterogeneity, as revealed by Levene's test, individual means were compared by Games Howell test. Horizontal brackets represent differences between groups in post-hoc comparison (**p<0.001, *p<0.05). n.e., not evaluable due to extremely low expression.