Neutrophils, the most abundant polymorphonuclear leukocytes, are critical first responders to infection, and have historically been underappreciated in terms of their functional complexity within the immune response. Once viewed primarily as short-lived, innate immune cells with limited functional plasticity, recent research has illuminated their considerable heterogeneity and diverse functional roles, which extend beyond their involvement in steady-state immunity. This review seeks to provide an updated analysis of neutrophil development, maturation, heterogeneity, and plasticity, with a focus on how these characteristics influence immune modulation in both healthy and diseased tissues. Beginning with the origin of neutrophils, we explore their maturation into effector cells and their evolving roles in immune defense under homeostatic and disease-associated conditions. We then delve into their heterogeneity, discussing recent breakthroughs in neutrophil research that challenge the traditional view of neutrophils as a uniform population. We address the significant advances that have been made in identifying distinct neutrophil subsets, the emerging complexities of their plasticity, and the challenges that remain in fully understanding their functional diversity. Finally, we highlight future directions and opportunities for continued exploration in this rapidly advancing field, shedding light on how these insights could open new avenues for therapeutic interventions.

Neutrophils are increasingly recognized as key contributors to the pathogenesis of Type 1 Diabetes (T1D), yet their precise mechanistic role in disease onset and progression remains incompletely understood. While these innate immune cells reside in pancreatic tissue and support tissue homeostasis under physiological conditions, they can also drive tissue damage by triggering innate immune responses and modulating inflammation. Within the inflammatory milieu, neutrophils establish complex, bidirectional interactions with various immune cells, including macrophages, dendritic cells, natural killer cells, and lymphocytes. Once activated, they may enhance the innate immune response through direct or indirect crosstalk with immune cells, antigen presentation, and β-cell destruction or dysfunction. These mechanisms underscore the multifaceted and dynamic role of neutrophils in T1D, shaped by their intricate immunological interactions. Further research into the diverse functional capabilities of neutrophils is crucial for uncovering novel aspects of their involvement in T1D, potentially revealing new therapeutic targets to modulate disease progression.

Aims/hypothesis: MiRNAs regulate gene expression, influencing beta cell function and pathways. Isoforms of miRNA (isomiRs), sequence variants of miRNAs with post-transcriptional modifications, exhibit cell-type-specific expression and functions. Despite their biological significance, a comprehensive isomiR profile in human pancreatic islets and beta cells remains unexplored. This study aims to profile isomiR expression in four beta cell sources: (1) laser capture microdissected human islets (LCM-HI); (2) collagenase-isolated human islets (CI-HI); (3) sorted beta cells; and (4) the EndoC-βH1 beta cell line, and to investigate their potential role in beta cell function. Methods: Small RNA-seq and/or small RNA dataset analysis was conducted on human pancreatic islets and beta cells. Data were processed using the sRNAbench bioinformatics pipeline to classify isomiRs based on sequence variations. A beta cell-specific isomiR signature was identified via cross-validation across datasets. Correlations between LCM-HI isomiR expression and in vivo clinical parameters were analysed using regression models. Functional validation of isomiR-411-5p-Ext5p(+1) was performed via overexpression in EndoC-βH1 cells and CI-HI, followed by glucose-stimulated insulin secretion (GSIS) assays and/or transcriptomic analysis. Results: IsomiRs constituted 59.2 ± 1.9% (LCM-HI), 59.6 ± 2.4% (CI-HI), 42.3 ± 7.2% (sorted beta cells) and 43.8 ± 1.2% (EndoC-βH1) of total miRNA reads (data represented as mean ± SD), with 3′ end trimming (Trim3p) being the predominant modification. A beta cell-specific isomiR signature of 30 sequences was identified, with isomiR-411-5p-Ext5p(+1) showing a significant inverse correlation with basal insulin secretion (p=0.0009, partial R ²=0.68) and total insulin secretion (p=0.005, partial R ²=0.54). Overexpression of isomiR-411-5p-Ext5p(+1), but not of its canonical counterpart, importantly reduced GSIS by 51% ( ± 15.2%; mean ± SD) (p=0.01) in EndoC-βH1 cells. Transcriptomic analysis performed in EndoC-βH1 cells and CI-HI identified 47 genes significantly downregulated by isomiR-411-5p-Ext5p(+1) (false discovery rate [FDR]<0.05) but not by the canonical miRNA, with enriched pathways related to Golgi vesicle biogenesis (FDR=0.017) and trans-Golgi vesicle budding (FDR=0.018). TargetScan analysis confirmed seed sequence-dependent target specificity for 81 genes uniquely regulated by the isomiR (p=1.1 × 10⁻⁹). Conclusions/interpretation: This study provides the first comprehensive isomiR profiling in human islets and beta cells, revealing their substantial contribution to miRNA regulation. IsomiR-411-5p-Ext5p(+1) emerges as a distinct key modulator of insulin secretion and granule dynamics in beta cells. These findings highlight isomiRs as potential biomarkers and therapeutic targets for diabetes, warranting further exploration of their roles in beta cell biology. Graphical

Aims: Angiotensin I‐converting enzyme type 2 (ACE2), a pivotal SARS‐CoV‐2 receptor, has been shown to be expressed in multiple cells, including human pancreatic beta‐cells. A putative bidirectional relationship between SARS‐CoV‐2 infection and diabetes has been suggested, confirming the hypothesis that viral infection in beta‐cells may lead to new‐onset diabetes or worse glycometabolic control in diabetic patients. However, whether ACE2 expression levels are altered in beta‐cells of diabetic patients has not yet been investigated. Here, we aimed to elucidate the in situ expression pattern of ACE2 in Type 2 diabetes (T2D) with respect to non‐diabetic donors which may account for a higher susceptibility to SARS‐CoV‐2 infection in beta‐cells.Material and Methods: Angiotensin I‐converting enzyme type 2 immunofluorescence analysis using two antibodies alongside insulin staining was performed on formalin‐fixed paraffin embedded pancreatic sections obtained from n = 20 T2D and n = 20 non‐diabetic (ND) multiorgan donors. Intensity and colocalisation analyses were performed on a total of 1082 pancreatic islets. Macrophage detection was performed using anti‐CD68 immunohistochemistry on serial sections from the same donors.Results: Using two different antibodies, ACE2 expression was confirmed in beta‐cells and in pancreas microvasculature. Angiotensin I‐converting enzyme type 2 expression was increased in pancreatic islets of T2D donors in comparison to ND controls alongside with a higher colocalisation rate between ACE2 and insulin using both anti‐ACE2 antibodies. CD68⁺ cells tended to be increased in T2D pancreata, in line with higher ACE2 expression observed in serial sections.Conclusions: Higher ACE2 expression in T2D islets might increase their susceptibility to SARS‐CoV‐2 infection during COVID‐19 in T2D patients, thus worsening glycometabolic outcomes and disease severity.

Neutrophils are increasingly recognized as key contributors to the pathogenesis of Type 1 Diabetes (T1D), yet their precise mechanistic role in disease onset and progression remains incompletely understood. While these innate immune cells reside in pancreatic tissue and support tissue homeostasis under physiological conditions, they can also drive tissue damage by triggering innate immune responses and modulating inflammation. Within the inflammatory milieu, neutrophils establish complex, bidirectional interactions with various immune cells, including macrophages, dendritic cells, natural killer cells, and lymphocytes. Once activated, they may enhance the innate immune response through direct or indirect crosstalk with immune cells, antigen presentation, and β-cell destruction or dysfunction. These mechanisms underscore the multifaceted and dynamic role of neutrophils in T1D, shaped by their intricate immunological interactions. Further research into the diverse functional capabilities of neutrophils is crucial for uncovering novel aspects of their involvement in T1D, potentially revealing new therapeutic targets to modulate disease progression.