Carnosine Activates Cellular Stress Response in Podocytes and Reduces Glycative and Lipoperoxidative Stress

Carnosine improves diabetic complications, including diabetic nephropathy, in in vivo models. To further understand the underlying mechanism of nephroprotection, we studied the effect of carnosine under glucose-induced stress on cellular stress response proteins in murine immortalized podocytes, essential for glomerular function. High-glucose stress initiated stress response by increasing intracellular heat shock protein 70 (Hsp70), sirtuin-1 (Sirt-1), thioredoxin (Trx), glutamate-cysteine ligase (gamma-glutamyl cysteine synthetase; γ-GCS) and heme oxygenase-1 (HO-1) in podocytes by 30–50% compared to untreated cells. Carnosine (1 mM) also induced a corresponding upregulation of these intracellular stress markers, which was even more prominent compared to glucose for Hsp70 (21%), γ-GCS and HO-1 (13% and 20%, respectively; all p < 0.001). Co-incubation of carnosine (1 mM) and glucose (25 mM) induced further upregulation of Hsp70 (84%), Sirt-1 (52%), Trx (35%), γ-GCS (90%) and HO-1 (73%) concentrations compared to untreated cells (all p < 0.001). The glucose-induced increase in 4-hydroxy-trans-2-nonenal (HNE) and protein carbonylation was reduced dose-dependently by carnosine by more than 50% (p < 0.001). Although podocytes tolerated high carnosine concentrations (10 mM), high carnosine levels only slightly increased Trx and γ-GCS (10% and 19%, respectively, compared to controls; p < 0.001), but not Hsp70, Sirt-1 and HO-1 proteins (p not significant), and did not modify the glucose-induced oxidative stress response. In podocytes, carnosine induced cellular stress tolerance and resilience pathways and was highly effective in reducing high-glucose-induced glycative and lipoperoxidative stress. Carnosine in moderate concentrations exerted a direct podocyte molecular protective action

Anserine and Carnosine Induce HSP70-Dependent H₂S Formation in Endothelial Cells and Murine Kidney

Anserine and carnosine have nephroprotective actions; hydrogen sulfide (H2S) protects from ischemic tissue damage, and the underlying mechanisms are debated. In view of their common interaction with HSP70, we studied possible interactions of both dipeptides with H2S. H2S formation was measured in human proximal tubular epithelial cells (HK-2); three endothelial cell lines (HUVEC, HUAEC, MCEC); and in renal murine tissue of wild-type (WT), carnosinase-1 knockout (Cndp1-KO) and Hsp70-KO mice. Diabetes was induced by streptozocin. Incubation with carnosine increased H2S synthesis capacity in tubular cells, as well as with anserine in all three endothelial cell lines. H2S dose-dependently reduced anserine/carnosine degradation rate by serum and recombinant carnosinase-1 (CN1). Endothelial Hsp70-KO reduced H2S formation and abolished the stimulation by anserine and could be restored by Hsp70 transfection. In female Hsp70-KO mice, kidney H2S formation was halved. In Cndp1-KO mice, kidney anserine concentrations were several-fold and sex-specifically increased. Kidney H2S formation capacity was increased 2–3-fold in female mice and correlated with anserine and carnosine concentrations. In diabetic Cndp1-KO mice, renal anserine and carnosine concentrations as well as H2S formation capacity were markedly reduced compared to non-diabetic Cndp1-KO littermates. Anserine and carnosine induce H2S formation in a cell-type and Hsp70-specific manner within a positive feedback loop with CN1

<i>Carnosinase-1</i> Knock-Out Reduces Kidney Fibrosis in Type-1 Diabetic Mice on High Fat Diet

Carnosine and anserine supplementation markedLy reduce diabetic nephropathy in rodents. The mode of nephroprotective action of both dipeptides in diabetes, via local protection or improved systemic glucose homeostasis, is uncertain. Global carnosinase-1 knockout mice (Cndp1-KO) and wild-type littermates (WT) on a normal diet (ND) and high fat diet (HFD) (n = 10/group), with streptozocin (STZ)-induced type-1 diabetes (n = 21–23/group), were studied for 32 weeks. Independent of diet, Cndp1-KO mice had 2- to 10-fold higher kidney anserine and carnosine concentrations than WT mice, but otherwise a similar kidney metabolome; heart, liver, muscle and serum anserine and carnosine concentrations were not different. Diabetic Cndp1-KO mice did not differ from diabetic WT mice in energy intake, body weight gain, blood glucose, HbA1c, insulin and glucose tolerance with both diets, whereas the diabetes-related increase in kidney advanced glycation end-product and 4-hydroxynonenal concentrations was prevented in the KO mice. Tubular protein accumulation was lower in diabetic ND and HFD Cndp1-KO mice, interstitial inflammation and fibrosis were lower in diabetic HFD Cndp1-KO mice compared to diabetic WT mice. Fatalities occurred later in diabetic ND Cndp1-KO mice versus WT littermates. Independent of systemic glucose homeostasis, increased kidney anserine and carnosine concentrations reduce local glycation and oxidative stress in type-1 diabetic mice, and mitigate interstitial nephropathy in type-1 diabetic mice on HFD

A Global Cndp1-Knock-Out Selectively Increases Renal Carnosine and Anserine Concentrations in an Age- and Gender-Specific Manner in Mice

Carnosinase 1 (CN1) is encoded by the Cndp1 gene and degrades carnosine and anserine, two natural histidine-containing dipeptides. In vitro and in vivo studies suggest carnosine- and anserine-mediated protection against long-term sequelae of reactive metabolites accumulating, e.g., in diabetes mellitus. We have characterized the metabolic impact of CN1 in 11- and 55-week-old Cndp1-knockout (Cndp1-KO) mice and litter-matched wildtypes (WT). In Cndp1-KO mice, renal carnosine and anserine concentrations were gender-specifically increased 2- to 9-fold, respectively in the kidney and both most abundant in the renal cortex, but remained unchanged in all other organs and in serum. Renal oxidized/reduced glutathione concentrations, renal morphology and function were unaltered. In Cndp1-KO mice at week 11, renal asparagine, serine and glutamine levels and at week 55, renal arginine concentration were reduced. Renal heat-shock-protein 70 (Hspa1a/b) mRNA declined with age in WT but not in Cndp1-KO mice, transcription factor heat-shock-factor 1 was higher in 55-week-old KO mice. Fasting blood glucose concentrations decreased with age in WT mice, but were unchanged in Cndp1-KO mice. Blood glucose response to intraperitoneal insulin was gender- but not genotype-dependent, the response to intraperitoneal glucose injection was similar in all groups. A global Cndp1-KO selectively, age- and gender-specifically, increases renal carnosine and anserine concentrations, alters renal amino acid- and HSP70 profile and modifies systemic glucose homeostasis. Increase of the natural occurring carnosine and anserine levels in the kidney by modulation of CN1 represents a promising therapeutic approach to mitigate or prevent chronic kidney diseases such as diabetic nephropathy

Representational scaffolding in digital simulations – learning professional practices in higher education

To advance the learning of professional practices in teacher education and medical education, this conceptual paper introduces the idea of representational scaffolding for digital simulations in higher education. We outline the ideas of core practices in two important fields of higher education, namely teacher and medical education. To facilitate future professionals’ learning of relevant practices, we emphasize the role of approximation of practice through the use of digital simulations, as they offer multiple options for selecting and adjusting representations of practice situations. Furthermore, we introduce the idea of representational scaffolding to adjust the demands of the learning task in simulations by selecting and modifying representations of practice to match relevant learner characteristics. Building on research on problem-solving and scientific reasoning, we identify leverage points for employing representational scaffolding. We suggest four sets of representational scaffolds that target relevant features of practice situations in simulations: informational complexity, typicality, required agency, and situation dynamics. Representational scaffolds might be implemented in a strategy for approximating practice that involves the media design, sequencing, and adaptation of representational scaffolding. The outlined conceptualization of representational scaffolding can systematize the design and adaptation of digital simulations in higher education and might contribute to the advancement of future professionals’ learning to further engage in professional practices. This conceptual paper offers a necessary foundation and terminology for approaching related future research. https://doi.org/10.1108/ILS-06-2022-007