Structural modifications of INGAP-PP present in HTD4010 peptide potentiate its effect on rat islet gene expression and insulin secretion.

Type 2 diabetes (T2D) is characterized by peripheral insulin resistance and altered insulin secretion due to a progressive loss of ß-cell mass and function. Today, most antidiabetic agents are designed to resolve impaired insulin secretion and/or insulin resistance, and only GLP-1-based formulations contribute to stopping the decline in ß-cell mass. HTD4010, a peptide carrying two modifications of the amino acid sequence of INGAP-PP (N-terminus acetylation and substitution of Asn13 by Ala) showed greater plasma stability and could be a good candidate for proposal as a drug that could improve ß cell mass and function lost in T2D. In the present study, we showed that HTD4010 included in the culture media of normal rat islets at a dose 100 times lower than that used for INGAP-PP was able to modulate, in the same way as the original peptide, both insulin secretion in response to glucose and the expression of key genes related to insular function, insulin and leptin intracellular pathways, neogenesis, apoptosis, and inflammatory response. Our results confirm the positive effect of HTD4010 on ß-cell function and gene expression of factors involved in the maintenance of ß-cell mass. Although new assays in animal models of prediabetes and T2D must be performed to be conclusive, our results are very encouraging, and they suggest that the use of HTD4010 at a dose 100 times lower than that of INGAP-PP could minimize its side effects in a future clinical trial.

Transcriptional signature of islet neogenesis-associated protein peptide-treated rat pancreatic islets reveals induction of novel long non-coding RNAs.

Background: Diabetes mellitus is characterized by chronic hyperglycemia with loss of ß-cell function and mass. An attractive therapeutic approach to treat patients with diabetes in a non-invasive way is to harness the innate regenerative potential of the pancreas. The Islet Neogenesis-Associated Protein pentadecapeptide (INGAP-PP) has been shown to induce ß-cell regeneration and improve their function in rodents. To investigate its possible mechanism of action, we report here the global transcriptional effects induced by the short-term INGAP-PP in vitro treatment of adult rat pancreatic islets. Methods and findings: Rat pancreatic islets were cultured in vitro in the presence of INGAP-PP for 4 days, and RNA-seq was generated from triplicate treated and control islet samples. We performed a de novo rat gene annotation based on the alignment of RNA-seq reads. The list of INGAP-PP-regulated genes was integrated with epigenomic data. Using the new gene annotation generated in this work, we quantified RNA-seq data profiled in INS-1 cells treated with IL1ß, IL1ß+Calcipotriol (a vitamin D agonist) or vehicle, and single-cell RNA-seq data profiled in rat pancreatic islets. We found 1,669 differentially expressed genes by INGAP-PP treatment, including dozens of previously unannotated rat transcripts. Genes differentially expressed by the INGAP-PP treatment included a subset of upregulated transcripts that are associated with vitamin D receptor activation. Supported by epigenomic and single-cell RNA-seq data, we identified 9 previously unannotated long noncoding RNAs (lncRNAs) upregulated by INGAP-PP, some of which are also differentially regulated by IL1ß and vitamin D in ß-cells. These include Ri-lnc1, which is enriched in mature ß-cells. Conclusions: Our results reveal the transcriptional program that could explain the enhancement of INGAP-PP-mediated physiological effects on ß-cell mass and function. We identified novel lncRNAs that are induced by INGAP-PP in rat islets, some of which are selectively expressed in pancreatic ß-cells and downregulated by IL1ß treatment of INS-1 cells. Our results suggest a relevant function for Ri-lnc1 in ß-cells. These findings are expected to provide the basis for a deeper understanding of islet translational results from rodents to humans, with the ultimate goal of designing new therapies for people with diabetes.