Figure 3.

At human C_max equivalent, linagliptin indirectly increases Ser16 phosphorylation of the Ca²⁺ handling protein phospholamban in cardiomyocytes. (A) Immunoblotting for serine 16 phosphorylated phospholamban (PLN(Ser16)) in heart homogenates of young, non-diabetic adult mice perfused with Krebs Henseleit buffer (KHB) or KHB supplemented with 9 nmol/L linagliptin and subjected to 20 min no-flow ischemia followed by 40 min reperfusion (n = 6/group). (B) Immunoblotting primary cultured mouse cardiomyocytes for PLN(Ser16) under control conditions or after incubation with 9 nmol/L linagliptin for 5 min (n = 13/condition). (C) Serial cut sections from a C57BL/6 mouse heart immunostained for DPP-4 or CD31 showing predominant DPP-4 expression in CD31+ cells indicative of endothelial expression (n = 4). Scale bar = 50 µm. (D–F) Volcano plots of differentially expressed genes determined by RNA sequencing of adult mouse cardiomyocytes derived from young, non-diabetic, non-high fat diet-fed mice (D; n = 5/condition) or aged, diabetic, high fat diet-fed (DM-HFD) mice (E; n = 3/condition) exposed to linagliptin (9 nmol/L) or vehicle for 24 h. (F) Volcano plot of differentially expressed genes in vehicle-treated cardiomyocytes derived from DM-HFD mice (n = 3) and control mice (n = 5). Values are mean ± S.D.. *p < 0.05 by two-tailed Student’s t-test.