A new approach for assessing cell composition in the human pancreas is detailed by Drawshy et al. (p. 554). The methodology, which is based on DNA methylation, addresses one of the major limitations of immunodetection of protein markers to detect particular cell types. Specifically, they are affected by physiological and pathological conditions (and technical issues), significantly complicating their use as a biomarker for cell numbers. Instead, the new approach relies on genomic loci that are uniquely demethylated in specific genomic locations in different cell types. They are also conserved, meaning they remain the same between different cell types and are only minimally affected by disease. Based on that notion, the authors describe the derivation of several DNA methylation biomarkers for a series of specific pancreatic cell types, including α-cells, β-cells, and δ-cells. They also report two methods to quantify cell numbers in pancreatic samples, with one based on PCR and follow-up next-generation sequencing and another that uses digital drop PCR (a cheaper and easier, but much less flexible, approach). They then applied the methodology to a series of islet preparations and pancreas samples to assess cell composition. Although primarily an article about methodology development, the analysis has already provided some biological insights, which the authors note are deserving of further investigation. For example, they found that insulin secretion per β-cell was similar in cultured islets obtained from donors with either type 1 or type 2 diabetes or individuals without diabetes but at risk. All three groups, however, had significantly lower insulin secretion levels than in islets obtained from donors without diabetes, indicating significant dysfunction. “The use of DNA methylation–based analysis not only provides a more accurate assessment of cell types in the human pancreas but also proves invaluable in interpreting insulin secretion assays,” said author Yuval Dor. “This method opens new avenues for understanding pancreas cell composition in both health and disease.”

Heat map showing methylation status of 20 loci that are differentially methylated in the indicated pancreas cell types.

Heat map showing methylation status of 20 loci that are differentially methylated in the indicated pancreas cell types.

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Drawshy et al. DNA methylation–based assessment of cell composition in human pancreas and islets. Diabetes 2024;73:554–564

A diet high in salt appears to accelerate and aggravate autoimmune diabetogenesis in nonobese mice, according to Ciou et al. (p. 592). Specifically, it seems that excessive salt intake drives diabetes progression via a SPAK (or STE20/SPS1-related proline/alanine–rich kinase)-dependent CD4+ T-cell mechanism in which an interleukin-21 (IL-21)–predominant phenotype drives T-cell pathogenicity. Crucially, it seems that SPAK can be inhibited pharmacologically, which results in the downregulation of salt-triggered IL-21. This would make it a potential therapeutic target in the common situation of excess salt intake driving autoimmune diabetes progression. “The Western diet favors autoimmune development, and overconsumption of salt is observed in children with type 1 diabetes,” said author Shin-Huei Fu. “We highlight that SPAK, which is highly expressed in T cells from patients with type 1 diabetes, may be responsible for increasing salt sensitivity and affects the risk of developing autoimmune diabetes or disease severity.” The findings come from a study involving nonobese mice that were fed either a high-salt diet or a normal-salt diet from 6 to 12 weeks of age and were monitored for diabetes development. The authors found that a high-salt diet accelerated diabetes progression and resulted in more severe insulitis compared with that of control mice on a normal-salt diet. They also found that transfer of CD4+ T cells from mice on a high-salt diet could accelerate diabetes progression and that expression of IL-21 and SPAK was significantly upregulated in mice on the high-salt diet. T-cell–specific knockout of SPAK attenuated diabetes development and resulted in the downregulation of IL-21 expression. The knockout also abolished salt-triggered diabetes acceleration, suggesting overall that SPAK has an essential role in saltassociated T-cell pathogenicity. “Our findings point to additional possible applications of SPAK modulation between the cross talk of cytokines with the excess salt milieu implicated for therapeutic strategies,” added Fu.

Representative hematoxylin-eosin–stained pancreatic sections and combined histological scores of insulitis from 12-week-old female NOD mice fed either normal-salt diet or high-salt diet.

Representative hematoxylin-eosin–stained pancreatic sections and combined histological scores of insulitis from 12-week-old female NOD mice fed either normal-salt diet or high-salt diet.

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Ciou et al. Excess salt intake activates IL-21–dominant autoimmune diabetogenesis via a salt-regulated Ste20-related proline/alanine-rich kinase in CD4 T cells. Diabetes 2024;73:592–603

Targeting four specific proteins could offer a route to developing treatment approaches for diabetic kidney disease (DKD), according to Zhang et al. (p. 618). They have identified CBLN1, COL6A2, ITIH3, and TGFBI as the targets and say that their use will provide guidance and direction toward targeted therapies for DKD. Treatment options for DKD are currently limited, with available options largely focused on managing symptoms. The findings come from a study that used a series of genetic data sets, Mendelian randomization, and a colocalization approach to sequentially narrow in on circulating proteins linked to DKD. They also used enrichment analysis to explore their biological significance and function and looked at the identified proteins’ druggability. Notably, the authors also used an external validation process on the identified proteins to enhance the credibility of the results. Initial Mendelian randomization analysis revealed 21 plasma proteins that have a causal relationship with DKD. Eleven were identified as risk proteins that may aggravate DKD. The remaining 10, however, appeared to be protective and potentially mitigate the risk of DKD. Colocalization analysis of the 21 proteins revealed 12 proteins that might share traits and causal variation with DKD. Enrichment analysis, including gene ontology and KEGG analyses, revealed a whole series of biological functions and metabolic pathways potentially associated with the identified proteins. The authors used assessment of druggability and external validation to identify the four proteins as having potential and relevant drug target properties for DKD. The authors go on to discuss why each protein is a potential therapeutic target for DKD and the research that is potentially needed to take them forward. For example, they cite lines of evidence that suggest TGFBI is a target for the transforming growth factor-β–targeting antibody LY-2382770, and reducing the level of ITIH3 or preventing its binding to hyaluronic acid is an approach to explore.

Zhang et al. Therapeutic targets for diabetic kidney disease: proteomewide Mendelian randomization and colocalization analyses. Diabetes 2024;73:618–627

A genetic variant in a gene previously associated with energy metabolism appears to alter several adiposityrelated traits, according to Huang et al. (p. 637). Specifically, switching the genotype of the variant rs10071329 from A/A to G/G resulted in enhanced PPARGC1B expression and, with it, improvements in a series of traits related to adiposity in human brown fat cells. Based on the findings, the authors suggest that the genetic variant will prove to be useful in a personalized genotype-based approach to treat obesity and even type 2 diabetes. Using CRISPR/Cas9 technology, the authors edited the alleles of the candidate variant in human brown adipocytes and, during and after differentiation, explored a series of metabolic characteristics and traits resulting from the change. The authors also used genome-wide genotyping on 132 Tanzanian women to look for correlations between rs10071329 and measures of adiposity. They found that switching the genotype of the variant from A/A to G/G enhanced the expression of PPARGC1B during differentiation and that this coincided with accumulation of triglycerides and greater expression of mitochondrial genes. The authors also found the G/G cells had improved mitochondrial respiration at baseline and after stimulation with norepinephrine. Glycerol release, indicative of improved lipolysis, was also increased following stimulation with norepinephrine. In terms of genotyping in Tanzanian women, nearly 95% had the A/A version of rs10071329, 3.8% had G/A, and 1.5% had G/G. There was a trend of association with BMI (P = 0.055) and an association with mid-upper arm circumference, with each copy of G allele associated with 3.0% lower BMI and 4.6% lower arm circumference. While clearly needing further research, the authors suggest the findings set the basis for “genotype-based precision medicine for obesity treatment” and note that the genotype of individuals could be indicative of who might benefit from lifestyle interventions.

Representative images of A/A- and G/G-edited cells stained with Oil Red O to assess lipid accumulation.

Representative images of A/A- and G/G-edited cells stained with Oil Red O to assess lipid accumulation.

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Huang et al. Human genetic variation at rs10071329 correlates with adiposityrelated traits, modulates PPARGC1B expression, and alters brown adipocyte function. Diabetes 2024;73:637–645

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