Toll-Like Receptor 7 Is Required for Lacrimal Gland Autoimmunity and Type 1 Diabetes Development in Male Nonobese Diabetic Mice

Abstract

Sjögren syndrome (SS) is an immunologically complex, chronic autoimmune disease targeting lacrimal and salivary glands. Nonobese diabetic (NOD) mice spontaneously develop inflammation of lacrimal and salivary glands with histopathological features similar to SS in humans including focal lymphocytic infiltrates in the affected glands. The innate immune signals driving lymphocytic infiltration of these glands are not well-defined. Here we evaluate the role of Toll-like receptor (TLR) 7 in the development of SS-like manifestations in NOD mice. We created a Tlr7 knockout NOD mouse strain and performed histological and gene expression studies to characterize the effects of TLR7 on autoimmunity development. TLR7 was required for male-specific lacrimal gland inflammation but not for female-specific salivary gland inflammation. Moreover, TLR7 was required for type 1 diabetes development in male but not female NOD mice. RNA sequencing demonstrated that TLR7 was associated with a type I interferon (IFN) response and a type I IFN-independent B cell response in the lacrimal glands. Together these studies identify a previously unappreciated pathogenic role for TLR7 in lacrimal gland autoimmunity and T1D development in male NOD mice adding to the growing body of evidence supporting sex differences in mechanisms of autoimmune disease in NOD mice.

Characterization of Type I Interferon-Associated Chemokines and Cytokines in Lacrimal Glands of Nonobese Diabetic Mice

“…Further studies are needed to more completely define the downstream consequences of type I IFN signaling and to specifically identify the lymphocytes and innate immune cells directly affected by the type I IFN signals. Moreover, the upstream signals driving the type I IFN response are also not fully elucidated, though our recent findings of a large common set of genes similarly upregulated in lacrimal glands in a TLR7-dependent manner suggest that TLR7 is one of those upstream type I IFN-inducing signals [60]. Ultimately, understanding the specific molecular mechanisms of type I IFN in SD-like autoimmunity may provide targets for novel therapeutics or for diagnostic or prognostic testing in SD and, potentially, other type I IFN-associated systemic autoimmune diseases.…”

“…This was done to prevent extreme outlier zero counts (i.e., dropouts) within the WT replicates from creating very large fold-change artifacts. Additional samples from TLR7 KO NOD mice were recently reported in comparison to these same WT samples [60]. Data have been deposited in NCBI's Gene Expression Omnibus [69] and are accessible through GEO Series accession number GSE161184 (https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc= GSE161184, accessed on 15 February 2021).…”

Nucleic acid-sensing toll-like receptors: Important players in Sjögren’s syndrome

“…The assessment of the contribution of TLR7 in the development of SS in the NOD mice, was done by deleting TLR7 in the NOD strain through CRISP/Cas9-mediated gene editing ( 74 ). Female TLR7-deficient NOD mice started developing diabetes at the age of 15 weeks, while male TLR7-deficient NOD mice did not develop diabetes ( 74 ).…”

“…The assessment of the contribution of TLR7 in the development of SS in the NOD mice, was done by deleting TLR7 in the NOD strain through CRISP/Cas9-mediated gene editing ( 74 ). Female TLR7-deficient NOD mice started developing diabetes at the age of 15 weeks, while male TLR7-deficient NOD mice did not develop diabetes ( 74 ). Evaluation of lacrimal and salivary gland inflammation in 10 weeks old mice, revealed that male TLR7-deficient NOD mice were protected from lacrimal inflammation, but surprisingly developed salivary gland inflammation compared to NOD mice ( 74 ).…”

“…Female TLR7-deficient NOD mice started developing diabetes at the age of 15 weeks, while male TLR7-deficient NOD mice did not develop diabetes ( 74 ). Evaluation of lacrimal and salivary gland inflammation in 10 weeks old mice, revealed that male TLR7-deficient NOD mice were protected from lacrimal inflammation, but surprisingly developed salivary gland inflammation compared to NOD mice ( 74 ). In contrast, female NOD mice developed focal sialadenitis regardless of the presence or absence of TLR7, while lacrimal gland inflammation was absent.…”