Lacrimal gland as the major source of mouse tear factors that are cytotoxic to corneal keratocytes

Visual fatigue a comprehensive review of mechanisms of occurrence, animal model design and nutritional intervention strategies

When the eyes work intensively, it is easy to have eye discomfort such as blurred vision, soreness, dryness, and tearing, that is, visual fatigue. Visual fatigue not only affects work and study efficiency, but long-term visual fatigue can also easily affect physical and mental health. In recent years, with the popularization of electronic products, although it has brought convenience to the office and study, it has also caused more frequent visual fatigue among people who use electronic devices. Moreover, studies have reported that the number of people with visual fatigue is showing a trend of increasing year by year. The range of people involved is also extensive, especially students, people who have been engaged in computer work and fine instruments (such as microscopes) for a long time, and older adults with aging eye function. More and more studies have proposed that supplementation with the proper nutrients can effectively relieve visual fatigue and promote eye health. This review discusses the physiological mechanisms of visual fatigue and the design ideas of animal experiments from the perspective of modern nutritional science. Functional food ingredients with the ability to alleviate visual fatigue are discussed in detail.

Chronic dry eye induced corneal hypersensitivity, neuroinflammatory responses, and synaptic plasticity in the mouse trigeminal brainstem

Background

Dry eye disease (DED) is a multifactorial disease associated with ocular surface inflammation, pain, and nerve abnormalities. We studied the peripheral and central neuroinflammatory responses that occur during persistent DED using molecular, cellular, behavioral, and electrophysiological approaches.

Methods

A mouse model of DED was obtained by unilateral excision of the extraorbital lachrymal gland (ELG) and Harderian gland (HG) of adult female C57BL/6 mice. In vivo tests were conducted at 7, 14, and 21 days (d) after surgery. Tear production was measured by a phenol red test and corneal alterations and inflammation were assessed by fluorescein staining and in vivo confocal microscopy. Corneal nerve morphology was evaluated by nerve staining. Mechanical corneal sensitivity was monitored using von Frey filaments. Multi-unit extracellular recording of ciliary nerve fiber activity was used to monitor spontaneous corneal nerve activity. RT-qPCR and immunostaining were used to determine RNA and protein levels at d21.

Results

We observed a marked reduction of tear production and the development of corneal inflammation at d7, d14, and d21 post-surgery in DED animals. Chronic DE induced a reduction of intraepithelial corneal nerve terminals. Behavioral and electrophysiological studies showed that the DED animals developed time-dependent mechanical corneal hypersensitivity accompanied by increased spontaneous ciliary nerve fiber electrical activity. Consistent with these findings, DED mice exhibited central presynaptic plasticity, demonstrated by a higher Piccolo immunoreactivity in the ipsilateral trigeminal brainstem sensory complex (TBSC). At d21 post-surgery, mRNA levels of pro-inflammatory (IL-6 and IL-1β), astrocyte (GFAP), and oxidative (iNOS2 and NOX4) markers increased significantly in the ipsilateral trigeminal ganglion (TG). This correlated with an increase in Iba1, GFAP, and ATF3 immunostaining in the ipsilateral TG of DED animals. Furthermore, pro-inflammatory cytokines (IL-6, TNFα, IL-1β, and CCL2), iNOS2, neuronal (ATF3 and FOS), and microglial (CD68 and Itgam) markers were also upregulated in the TBSC of DED animals at d21, along with increased immunoreactivity against GFAP and Iba1.

Conclusions

Overall, these data highlight peripheral sensitization and neuroinflammatory responses that participate in the development and maintenance of dry eye-related pain. This model may be useful to identify new analgesic molecules to alleviate ocular pain.

A new dry eye mouse model produced by exorbital and intraorbital lacrimal gland excision

Chronic dry eye is an increasingly prevalent condition worldwide, with resulting loss of visual function and quality of life. Relevant, repeatable, and stable animal models of dry eye are still needed. We have developed an improved surgical mouse model for dry eye based on severe aqueous fluid deficiency, by excising both the exorbital and intraorbital lacrimal glands (ELG and ILG, respectively) of mice. After ELG plus ILG excision, dry eye symptoms were evaluated using fluorescein infiltration observation, tear production measurement, and histological evaluation of ocular surface. Tear production in the model mice was significantly decreased compared with the controls. The corneal fluorescein infiltration score of the model mice was also significantly increased compared with the controls. Histological examination revealed significant severe inflammatory changes in the cornea, conjunctiva or meibomian glands of the model mice after surgery. In the observation of LysM-eGFP^(+/−) mice tissues, postsurgical infiltration of green fluorescent neutrophils was observed in the ocular surface tissues. We theorize that the inflammatory changes on the ocular surface of this model were induced secondarily by persistent severe tear reduction. The mouse model will be useful for investigations of both pathophysiology as well as new therapies for tear-volume-reduction type dry eye.

Bilateral central toxic keratopathy after laser in situ keratomileusis

One week after LASIK, our patient presented with bilateral haloes and reduced vision. Examination revealed the typical central toxic keratopathy triad: corneal thinning, hyperopic shift and a reduction in best corrected visual acuity to 6/12, which, after commencing high-dose topical steroids, improved 6 months later to 6/6.

Comparative Proteomics of Mouse Tears and Saliva: Evidence from Large Protein Families for Functional Adaptation

We produced a tear proteome of the genome mouse, C57BL/6, that contained 139 different protein identifications: 110 from a two-dimensional (2D) gel with subsequent trypsin digestion, 19 from a one-dimensional (1D) gel with subsequent trypsin digestion and ten from a 1D gel with subsequent Asp-N digestion. We compared this tear proteome with a C57BL/6 mouse saliva proteome produced previously. Sixteen of the 139 tear proteins are shared between the two proteomes, including six proteins that combat microbial growth. Among the 123 other tear proteins, were members of four large protein families that have no counterparts in humans: Androgen-binding proteins (ABPs) with different members expressed in the two proteomes, Exocrine secreted peptides (ESPs) expressed exclusively in the tear proteome, major urinary proteins (MUPs) expressed in one or both proteomes and the mouse-specific Kallikreins (subfamily b KLKs) expressed exclusively in the saliva proteome. All four families have members with suggested roles in mouse communication, which may influence some aspect of reproductive behavior. We discuss this in the context of functional adaptation involving tear and saliva proteins in the secretions of mouse lacrimal and salivary glands, respectively.

Did androgen-binding protein paralogs undergo neo- and/or Subfunctionalization as the Abp gene region expanded in the mouse genome?

The Androgen-binding protein (Abp) region of the mouse genome contains 30 Abpa genes encoding alpha subunits and 34 Abpbg genes encoding betagamma subunits, their products forming dimers composed of an alpha and a betagamma subunit. We endeavored to determine how many Abp genes are expressed as proteins in tears and saliva, and as transcripts in the exocrine glands producing them. Using standard PCR, we amplified Abp transcripts from cDNA libraries of C57BL/6 mice and found fifteen Abp gene transcripts in the lacrimal gland and five in the submandibular gland. Proteomic analyses identified proteins corresponding to eleven of the lacrimal gland transcripts, all of them different from the three salivary ABPs reported previously. Our qPCR results showed that five of the six transcripts that lacked corresponding proteins are expressed at very low levels compared to those transcripts with proteins. We found 1) no overlap in the repertoires of expressed Abp paralogs in lacrimal gland/tears and salivary glands/saliva; 2) substantial sex-limited expression of lacrimal gland/tear expressed-paralogs in males but no sex-limited expression in females; and 3) that the lacrimal gland/tear expressed-paralogs are found exclusively in ancestral clades 1, 2 and 3 of the five clades described previously while the salivary glands/saliva expressed-paralogs are found only in clade 5. The number of instances of extremely low levels of transcription without corresponding protein production in paralogs specific to tears and saliva suggested the role of subfunctionalization, a derived condition wherein genes that may have been expressed highly in both glands ancestrally were down-regulated subsequent to duplication. Thus, evidence for subfunctionalization can be seen in our data and we argue that the partitioning of paralog expression between lacrimal and salivary glands that we report here occurred as the result of adaptive evolution.

Anterior Segment Optical Coherence Tomography Imaging of Central Toxic Keratopathy

The authors report anterior segment optical coherence tomography (OCT) imaging findings in a case of central toxic keratopathy following laser in situ keratomileusis (LASIK) surgery for low hyperopia. OCT imaging 1 month after surgery demonstrates that the flap thickness is maintained and the location of stromal tissue loss is just posterior to the flap in the stromal bed in the affected area. This corresponds to the clinical observation of interface opacity extending posteriorly into the stroma as first described by Sonmez and Maloney1 in their initial description of the syndrome. Follow-up OCT imaging 3 months later revealed interval decrease in stromal thinning. The etiology of this syndrome is unknown.

Apoptosis in the initiation, modulation and termination of the corneal wound healing response

Stromal keratocyte apoptosis has been well-characterized as an early initiating event of the corneal wound healing response, triggering subsequent cellular processes that include bone marrow-derived cell infiltration, proliferation and migration of residual keratocyte cells, and, in some circumstances, generation of myofibroblast cells. Recent studies, however, have suggested a more general role for apoptosis in the overall stromal wound healing response that includes modulation and termination functions. This review article highlights, and ties together, recent studies that have demonstrated the important role apoptosis likely plays in weeks to months following an initial insult to the cornea-depending on the type and extent of corneal injury.

Mechanical damage to corneal stromal cells by epithelial scraping

OBJECTIVE

Corneal epithelial scraping, a common clinical procedure, triggers a loss of underlying keratocytes. This study was conducted to examine whether the physical impact of epithelial scrape injury plays any role in the death of these cells.

METHODS

Epithelial debridement was carried out on the cornea of a freshly killed mouse either by mechanical scraping with a blunt spatula, as in the clinical scraping, or lifting by repeated touching with a gelatin-coated slide. Subsequently, nuclei, nuclear envelope, microtubules, microfilaments, and plasma membranes were examined with specific probes. Some corneas were fixed with alcohol before scrape injury. Fate of keratocytes after epithelial injury was investigated with isolated eyes ex vivo and living mice in vivo. Some of the procedures were performed with human donor corneas.

RESULTS

Within seconds of, or possibly simultaneous to, mechanical epithelial scraping, nuclei of underlying keratocytes became grossly deformed to assume extremely stretched morphology, accompanied by destruction of microfilaments and microtubules as well as compromised plasma membranes. These cells deteriorated gradually over several hours both ex vivo and in vivo. Nuclear deformation was observed even when the cornea was fixed with alcohol before epithelial scraping. When the epithelium was removed by gentle lifting, nuclei remained mostly intact. Similar results were obtained with human donor corneas.

CONCLUSION

Mechanical epithelial scraping can cause immediate damage to underlying anterior keratocytes by a physical impact, which appears to lead to degeneration of these cells.