COVID-19 commonly presents as pneumonia, with those most severely affected progressing to respiratory failure. Patient responses to SARS-CoV-2 infection are varied, with comorbidities acting as major contributors to varied outcomes. Focusing on one such major comorbidity, we assessed whether pharmacological induction of type 1 diabetes mellitus (T1DM) would increase the severity of lung injury in a murine model of COVID-19 pneumonia utilizing wild-type mice infected with mouse-adapted SARS-CoV-2. Hyperglycemic mice exhibited increased weight loss and reduced blood oxygen saturation in comparison with their euglycemic counterparts, suggesting that these animals indeed experienced more severe lung injury. Transcriptomic analysis revealed a significant impairment of the adaptive immune response in the lungs of diabetic mice compared with those of control. To expand the limited options available for tissue analysis due to biosafety restrictions, we also employed a new technique to digest highly fixed tissue into a single-cell suspension, originally designed for scRNA-Seq, which we then adapted for flow cytometric analysis. Flow immunophenotyping and scRNA-Seq confirmed impaired recruitment of T-cells into the lungs of T1DM animals. In addition, scRNA-Seq revealed a distinct, highly inflammatory macrophage profile in the diabetic cohort that correlates with the more severe infection these mice experienced clinically, allowing insight into a possible mechanism for this phenomenon. Recognizing the near certainty that respiratory viruses will continue to present significant public health concerns for the foreseeable future, our study provides key insights into how T1DM results in a much more severe infection and identifies possible targets to ameliorate comorbidity-associated severe disease.NEW & NOTEWORTHY We define the exacerbating effects of type 1 diabetes mellitus (T1DM) on COVID-19 pneumonia severity in mice. Hyperglycemic mice experienced increased weight loss and reduced oxygen saturation. Transcriptomic analysis revealed impaired immune responses in diabetic mice, while flow cytometry and single-cell RNA sequencing confirmed reduced T-cell recruitment and an inflammatory macrophage profile. In addition, we introduced a novel technique for tissue analysis, enabling flow cytometric analysis on highly fixed tissue samples.
Keywords: COVID; alveolar macrophages; lung injury; type 1 diabetes.