Detection of cationic amino acid transporters
in the human lacrimal system and their involvement in ocular surface disease
Kristin Jaeger 1,
Ulrike Boenisch 1,
Michaela Risch 1,
Dieter Worlitzsch 2,
and
Friedrich P. Paulsen 3*
1 Department of Anatomy and Cell Biology, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
2 Deparment of Hygiene, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
3 Dept. Anatomy & Cell Biology, Martin-Luther-University of Halle-Wittenberg, Große Steinstr. 52, Halle (Saale), 06097, Germany
* To whom correspondence should be addressed. E-mail: friedrich.paulsen{at}medizin.uni-halle.de.
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Abstract |
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Purpose. To evaluate the presence and role of human cationic amino acid
transporters (hCATs) at the ocular surface in healthy and pathologic states and under experimental inflammatory conditions.
Methods. Expression of mRNA for hCATs 1, 2, and 3 (SLC7A1, -A2, and -A3) was
analyzed by RT-PCR in healthy lacrimal gland, conjunctiva, cornea and nasolacrimal ducts as well as in a SV40 immortalized corneal epithelial cell line (HCE; Araki-Sasaki cell line). Localization of hCAT1 and hCAT2 was determined by
immunohistochemistry in healthy tissues and in sections of different corneal
pathologies including keratoconus, Fuchs' dystrophy and herpetic keratitis. Cultured
corneal epithelial cells were stimulated with proinflammatory cytokines and
supernatants of Staphylococcus aureus and Pseudomonas aeruginosa and analyzed
by real-time PCR.
Results. Expression of both hCAT1 and hCAT2 mRNA, but not of hCAT3 mRNA,
were detected in healthy conjunctiva, cornea and nasolacrimal ducts. Human lacrimal gland revealed only hCAT2 mRNA expression. Immunohistochemistry demonstrated presence of both hCAT1 and hCAT2 in epithelial cells of cornea, conjunctiva and nasolacrimal ducts. Goblet cells revealed no reactivity. Moreover, hCAT2 was visible in acinar cells of lacrimal gland. No changes in the staining reactivity were obtained for hCAT1 in different corneal pathologies. In contrast, hCAT2 showed increased subjective staining intensity in all corneal pathologies. Cell culture experiments revealed that tumour necrosis factor 
and supernatant of S. aureus increased hCAT1 and hCAT2 expression significantly. Supernatant of P. aeruginosa led to an increase in hCAT2-expression only.
Conclusion: Our results show for the first time the distribution of hCATs in tissues of the ocular surface and lacrimal apparatus. Both transporters seem to be differently regulated under pathological conditions of the ocular surface. Their physiological functions in amino acid transport make them potential candidates for therapeutic intervention.
Key Words:
tear film, corneal epithelium, conjunctiva, lacrimal gland, CAT, amino acid transporters
