Targeting APLN/APJ restores blood-testis barrier and improves spermatogenesis in murine and human diabetic models

Type 2 diabetes mellitus is one of the most prevalent metabolic diseases affecting multiple organs, including reproductive disorders in male diabetic patients. However, the molecular mechanisms that contribute to spermatogenesis dysfunction in diabetic patients have not yet been fully elucidated. Here, we performed Smart-seq2 to examine the transcriptome of diabetic patients' testis cells at single cell resolution including all major cell types of the testis. Intriguingly, whereas spermatogenesis appears largely preserved, the gene expression profiles of Sertoli cells and the blood-testis barrier (BTB) structure were dramatically impaired. Among the deregulated pathways, the Apelin (APLN) peptide /Apelin-receptor (APJ) axis was hyper-activated in diabetic patients. Mechanistically, APLN is produced locally by Sertoli cells upon high glucose treatment, which subsequently suppressed the production of carnitine and repressed the expression of cell adhesion genes in Sertoli cells. Together, these effects culminated in BTB structural dysfunction. Finally, using the small molecule APLN receptor antagonist, ML221, we show that blocking APLN/APJ significantly ameliorated the BTB damage and, importantly, improved functional spermatogenesis in diabetic db/db mice. We also translated and validated these findings in cultured human testis. Our findings identify the APLN/APJ axis as a promising therapeutic target to improve reproduction capacity in male diabetic patients. Here we performed scRNA sequencing for 900 individual human testicular cells including spermatogonia, spermatocytes, spermatids, and testicular somatic cells (soma) from donors with diabetes mellitus. The normal samples used in this study are from GSE106487 (GSM2838842-GSM2838908). To better integrate the normal samples and the diabetes samples, the raw data of the normal samples were re-analyzed using an analysis process consistent with that of the diabetes samples. **Note from submitter: Due to the Regulations of the People's Republic of China on the Management of Human Genetic Resources, raw data related to humans needs to be uploaded to the National Genomics Data Center, China National Center for Bioinformation (CNCB-NGDC), so we cannot upload raw data to NCBI.** The raw data is stored at https://ngdc.cncb.ac.cn/gsa-human/ , and the accession number is HRA000976.