Revealing the Angiopathy of Lacrimal Gland Lesion in Type 2 Diabetes

Characterization and Role of Glucagon-Like Peptide 1 Receptor in the Lacrimal Gland: Novel Insights into Diabetic Dry Eye Pathogenesis

This study aimed to investigate the expression of glucagon-like peptide 1 receptor (GLP-1R) in the lacrimal gland and explore the effects of topical application of GLP-1R agonist on lacrimal gland function in a murine model of type 1 diabetes. Tear secretion was evaluated using phenol red threads, RNA sequencing was used to explore gene expression profiles associated with hyperglycemia-induced lacrimal gland injuries, and histologic analysis was conducted to evaluate the degree of damage. The expression of GLP-1R in the lacrimal gland was first identified, and a down-regulation trend associated with diabetes was observed. RNA-sequencing data from lacrimal gland tissues revealed that differentially expressed genes were enriched in inflammatory response pathways. Histologic analysis demonstrated persistent hyperglycemia-induced infiltration of inflammatory cells and progressive fibrosis in the lacrimal gland, resulting in atrophy and diminished tear secretion. Topical application of liraglutide effectively attenuated inflammation and alleviated fibrosis, thus promoting tear production in diabetic mice. Additionally, local intervention with liraglutide promoted autophagy degradation function in the lacrimal gland. This study represents the first validation of GLP-1R expression in the lacrimal gland and its down-regulation induced by diabetes. Additionally, these findings demonstrate that topical administration of liraglutide eye drops, a GLP-1R agonist, can effectively mitigate hyperglycemia-induced damage in the lacrimal gland while enhancing tear secretion.

Analysis of the heterogeneity and complexity of murine extraorbital lacrimal gland via single-cell RNA sequencing

PURPOSE

The lacrimal gland is essential for maintaining ocular surface health and avoiding external damage by secreting an aqueous layer of the tear film. However, a healthy lacrimal gland's inventory of cell types and heterogeneity remains understudied.

METHODS

Here, 10X Genome-based single-cell RNA sequencing was used to generate an unbiased classification of cellular diversity in the extraorbital lacrimal gland (ELG) of C57BL/6J mice. From 43,850 high-quality cells, we produced an atlas of cell heterogeneity and defined cell types using classic marker genes. The possible functions of these cells were analyzed through bioinformatics analysis. Additionally, the CellChat was employed for a preliminary analysis of the cell-cell communication network in the ELG.

RESULTS

Over 37 subclasses of cells were identified, including seven types of glandular epithelial cells, three types of fibroblasts, ten types of myeloid-derived immune cells, at least eleven types of lymphoid-derived immune cells, and five types of vascular-associated cell subsets. The cell-cell communication network analysis revealed that fibroblasts and immune cells play a pivotal role in the dense intercellular communication network within the mouse ELG.

CONCLUSIONS

This study provides a comprehensive transcriptome atlas and related database of the mouse ELG.

Moderate-severe peripheral neuropathy in diabetes associated with an increased risk of dry eye disease

SIGNIFICANCE

This study establishes an increased risk of developing dry eye disease (DED) in patients with diabetic peripheral neuropathy using validated diagnostic criteria for both conditions.

PURPOSE

The disruption of ocular surface homeostasis has been associated with diabetes. However, it remains unclear if this association is independently influenced by peripheral neuropathy secondary to diabetes. This study aimed to investigate the clinical signs and symptoms of DED and their association with the severity of peripheral neuropathy in participants with type 2 diabetes.

METHODS

This prospective cross-sectional study recruited 63 participants with type 2 diabetes. All participants underwent a detailed assessment of DED using dry eye questionnaires (Ocular Surface Disease Index, Dry Eye Questionnaire-5), tear osmolarity, lipid layer thickness, noninvasive keratographic tear breakup time, phenol red thread test (PRT), and ocular surface staining. Corneal nerve morphology was imaged using corneal confocal microscopy. Based on the Total Neuropathy Scale, participants were stratified into no/mild (n = 48) and moderate/severe (n = 15) neuropathy groups.

RESULTS

Dry eye disease was diagnosed in 31 participants (50%) of the total cohort, and the odds of developing DED in the moderate/severe neuropathy group were four times (95% confidence interval, 1.10 to 13.80; p=0.030) higher compared with the no/mild neuropathy group. The Dry Eye Questionnaire-5 scores were significantly higher (p=0.020), and PRT values (p=0.048) and corneal nerve fiber length (p<0.001) were significantly reduced in the moderate/severe neuropathy group compared with the no/mild neuropathy group. In regression analysis, neuropathy scores were independently associated with PRT measurements ( β = -0.333, p=0.023) and nerve fiber length ( β = -0.219, p=0.012) while adjusting for age, gender, hemoglobin A 1c , and duration of diabetes.

CONCLUSIONS

Type 2 diabetic patients with peripheral neuropathy have a risk of developing DED, which increases with the severity of neuropathy. The observation that worsening peripheral neuropathy is associated with reduced tear secretion suggests that it may contribute to aqueous insufficiency.

Topical naltrexone increases aquaporin 5 production in the lacrimal gland and restores tear production in diabetic rats

Diabetes mellitus is a prevalent disease that is often accompanied by ocular surface abnormalities including delayed epithelial wound healing and decreased corneal sensitivity. The impact of diabetes on the lacrimal functional unit (LFU) and the structures responsible for maintaining tear homeostasis, is not completely known. It has been shown that the Opioid Growth Factor Receptor (OGFr), and its ligand, Opioid Growth Factor (OGF), is dysregulated in the ocular surface of diabetic rats leading to overproduction of the inhibitory growth peptide OGF. The opioid antagonist naltrexone hydrochloride (NTX) blocks the OGF-OGFr pathway, and complete blockade following systemic or topical treatment with NTX restores the rate of re-epithelialization of corneal epithelial wounds, normalizes corneal sensitivity, and reverses dry eye in diabetic animal models. These effects occur rapidly and within days of initiating treatment. The present study was designed to understand mechanisms related to the fast reversal (<5 days) of dry eye by NTX in type 1 diabetes (T1D) by investigating dysregulation of the LFU. The approach involved examination of the morphology of the LFU before and after NTX treatment. Male and female adult Sprague-Dawley rats were rendered hyperglycemic with streptozotocin, and after 6 weeks rats were considered to be a T1D model. Rats received topical NTX twice daily to one eye for 10 days. During the period of treatment, tear production and corneal sensitivity were recorded. On day 11, animals were euthanized and orbital tissues including conjunctiva, eyelids, and lacrimal glands, were removed and processed for histologic examination including immunohistochemistry. Male and female T1D rats had significantly decreased tear production and corneal insensitivity, significantly decreased number and size of lacrimal gland acini, decreased expression of aquaporin-5 (AQP5) protein and decreased goblet cell size. Thus, 10 days of NTX treatment restored tear production and corneal sensitivity to normal values, increased AQP5 expression, and restored the surface area of goblet cells to normal. NTX had no effect on the number of lacrimal gland acini or the number of conjunctival goblet cells. In summary, blockade of the OGF-OGFr pathway with NTX reversed corneal and lacrimal gland complications and restored some components of tear homeostasis confirming the efficacy of topical NTX as a treatment for ocular defects in diabetes.

Electroacupuncture regulates the P2X7R-NLRP3 inflammatory cascade to relieve decreased sensation on ocular surface of type 2 diabetic rats with dry eye

Dry eye (DE) is a prevalent ocular surface disease in patients with type 2 diabetes (T2DM). However, current medications are ineffective against decreased sensation on the ocular surface. While electroacupuncture (EA) effectively alleviates decreased sensation on ocular surface of DE in patients with T2DM, the neuroprotective mechanism remains unclear. This study explored the pathogenesis and therapeutic targets of T2DM-associated DE through bioinformatics analysis. It further investigated the underlying mechanism by which EA improves decreased sensation on the ocular surface of DE in rats with T2DM. Bioinformatic analysis was applied to annotate the potential pathogenesis of T2DM DE. T2DM and DE was induced in male rats. Following treatment with EA and fluorometholone, comprehensive metrics were assessed. Additionally, the expression patterns of key markers were studied. Key targets such as NLRP3, Caspase-1, and NOD-like receptor signaling may be involved in the pathogenesis of T2DM DE. EA treatment improved ocular measures. Furthermore, EA potently downregulated P2X7R, NLRP3, apoptosis-associated speck-like protein containing a CARD (ASC), and Caspase-1 expression within the trigeminal ganglion and spinal trigeminal nucleus caudalis. Targeted P2X7R antagonist (A-438079) and agonist (BzATP) employed as controls to decipher the biochemistry of the therapeutic effects of EA showed an anti-inflammatory effect with A-438079, while BzATP blocked the anti-inflammatory effect of EA. EA relieved DE symptoms and attenuated inflammatory damage to sensory nerve pathways in T2DM rats with DE. These findings suggest a crucial role of EA inhibition of the P2X7R-NLRP3 inflammatory cascade to provide these benefits.

Establishment of mouse model of neurotrophic keratopathy through TRPV1 neuronal ablation

Neurotrophic keratopathy (NK) is a challenging disease with the reduced innervation to the cornea. To establish a genetic and stable mouse model of NK, we utilized the TRPV1-DTR mice with intraperitoneal injection of diphtheria toxin (DT) to selectively eliminate TRPV1 neurons. After DT administration, the mice exhibited robust ablation of TRPV1 neurons in the trigeminal ganglion, accompanied with reduced corneal sensation and nerve density, as well as the decreased calcitonin-gene-related peptide (CGRP) and substance P levels. According to disease progression of TRPV1 neuronal ablation, tear secretion was reduced from day 3, which followed by corneal epithelial punctate lesions from day 7. From day 11 to day 16, the mice exhibited persistent corneal epithelial defects and stromal edema. By day 21, corneal ulceration and stromal melting were observed with the abundant inflammatory cell infiltration, corneal neovascularization, and enhanced cell apoptosis. Moreover, subconjunctival injection of CGRP delayed the NK progression with the characteristics of reduced severe corneal epithelial lesions and corneal inflammation. In addition, the impairments of conjunctival goblet cells, lacrimal gland, and meibomian gland were identified by the diminished expression of MUC5AC, AQP5, and PPARγ, respectively. Therefore, these results suggest that the TRPV1-DTR mice may serve as a reliable animal model for the research of NK pathogenesis.

Artificial Intelligence-Assisted Bioinformatics, Microneedle, and Diabetic Wound Healing: A "New Deal" of an Old Drug

Diabetic wounds severely influence life, facing grand challenges in clinical treatments. The demand for better treatment is growing dramatically. Diabetic wound healing is challenging because of inflammation, angiogenesis disruptions, and tissue remodeling. Based on sequencing results of diabetic patients' skins and artificial intelligence (AI)-assisted bioinformatics, we excavate a potential therapeutic agent Trichostatin A (TSA) and a potential target histone deacetylase 4 (HDAC4) for diabetic wound healing. The molecular docking simulation reveals the favorable interaction between TSA and HDAC4. Taking advantage of the microneedle (MN) minimally invasive way to pierce the skin barrier for drug administration, we develop a swelling modified MN-mediated patch loaded with TSA to reduce the probability of injection-caused iatrogenic secondary damage. The MN-mediated TSA patch has been demonstrated to reduce inflammation, promote tissue regeneration, and inhibit HDAC4, which provides superior results in diabetic wound healing. We envisage that our explored specific drug TSA and the related MN-mediated drug delivery system can provide an innovative approach for diabetic wound treatment with simple, effective, and safe features and find a broad spectrum of applications in related biomedical fields.

Inhibition of Gli1 suppressed hyperglycemia-induced meibomian gland dysfunction by promoting pparγ expression

Diabetes is one of the risk factors for meibomian gland dysfunction (MGD); however, the underlying molecular mechanism remains unknown. The current study aims to examine the effects of glioma-associated oncogene homolog 1 (Gli1), a transcription factor of the sonic hedgehog (Shh) pathway, in the modulation of diabetic-related MGD. Here, using RNA sequencing and qRT-PCR, we examined the mRNA changes of Shh pathway involving genes. mRNA sequencing analysis showed that the Shh pathway involving genes Shh and Gli1 were markedly upregulated in diabetic MG, and qRT-PCR detection of Shh pathway-associated genes found that Gli1 expression increased most significantly. Contrary to the elevation of Gli1 level, the expression of pparγ was downregulated in diabetic MG and in high glucose treated organotypic cultured mouse MG. GANT61, an inhibitor of Gli1, effectively inhibited the reduction of pparγ expression and lipid accumulation induced by high glucose, which was suppressed by pparγ inhibitor T0070907. We further demonstrated that advanced glycation end products (AGEs) treatment also promoted the expression of Gli1 and pparγ in organotypic cultured mouse MG. AGEs inhibitor Aminoguanidine suppressed high glucose caused Gli1 upregulation in organotypic cultured mouse MG. These results suggest that suppression of Gli1 may be a potentially useful therapeutic option for diabetic-related MGD.