Abstrak

Keratoconus ( KC ) adalah ectasia paling umum dari kornea dan merupakan alasan umum untuk transplantasi kornea. Strategi terapi yang dapat menghentikan perkembangan penyakit ini dan memodifikasi patogenesis yang mendasari menjadi semakin populer di kalangan ilmuwan. Akumulasi data merupakan bukti kuat dari peran genetik dalam patogenesis KC. Lokus yang berbeda telah diidentifikasi, dan mutasi tertentu juga telah dipetakan untuk penyakit ini. Selain itu, sifat biofisik kornea itu sendiri yang membuat ia sesuai dengan jaringan untuk terapi gen. Keistimewaan dari terapi ini adalah peningkatan kekebalan tubuh dan ex vivo stabilitas. Keuntungan terbaru di vektor, selain kemampuan untuk memodulasi lingkungan kornea untuk menerima gen sasaran untuk jangka waktu lama, terapi ini juga memberikan harapan yang besar untuk hasil luar biasa.

Kata kunci : Kornea , terapi gen , genetika , keratoconus

PengenalanKeratoconus (KC) adalah penyakit yang berhubungan dengan peradangan progresif kornea. Penyakit ini biasanya dimulai pada masa pubertas dan manifestasinya terlihat pada usia 30 hingga 40 tahun.[ 1 ] KC dianggap sebagai ectasia kornea yang paling umum [ 2 ] dengan insiden diperkirakan dalam masyarakat yang berbeda berkisar dari 5 sampai 20 dari 10.000 orang dan prevalensi 54 dari 100.000 dilaporkan menurut studi yang berbeda. [ 3 ] , [ 4 ] KC dianggap memiliki dasar genetik. Banyak gen termasuk sistem penglihatan homeoboks 1 ( VSX1 ) gen , superoxide dismutase 1 ( SOD1 ) gen dan lysyl oksidase ( LOX ), dan mutasi genetik yang terkait dengan KC dalam beberapa penelitian . Studi hubungan di keluarga dengan KC, studi hubungan genome - wide dan studi kembar juga menemukan bahwa ada kecenderungan genetik untuk KC . [ 5 ] , [ 6 ] , [ 7 ] , [ 8 ] , [ 9 ] , [ 10 ] Temuan ini memberikan ide untuk terapi gen sebagai pilihan pengobatan yang mungkin untuk KC.

MetodeTujuan pembuatan karya tulis ilmiah ini adalah untuk menjelaskan bahwa terapi gen dapat digunakan untuk pengobatan keratoconus. Kami mencari data-data dari literatur berbahasa Inggris dengan ulasan dan referensi yang menyertainya. Kata-kata pencarian utama diantaranya: genetik KC, terapi gen dari KC, pengobatan genetik KC, perspektif KC, studi molekuler dari KC, manajemen dan pilihan pengobatan KC, diagnosis KC. Selain itu, kutipan dari pencarian di atas juga disertakan.

PatogenesisPatofisiologi pasti KC sampai sekarang belum diketahui. Interaksi antara faktor lingkungan dan genetik tampaknya berperan. Pada pasien yang rentan faktor lingkungan seperti trauma, ultraviolet atau atopi memicu kaskade inflamasi yang menyebabkan degenerasi stroma kornea. [11]

Ketidakseimbangan antara agen pro-inflamasi dan agen anti-inflamasi telah ditemukan. Pada keratinosit kornea dari KC pasien, Interleukin 1 reseptor ditemukan empat kali lebih dari keratinosit normal. Sitokin ini menginduksi apoptosis keratinosit dan mengatur proliferasi keratinosit dan diferensiasi. [12], [13] adhesi antar-molekul 1, Vascular adhesi sel molekul-1 dan interleukin 6 bahkan dapat mencapai 40 kali, sedangkan ekspresi agen anti-inflamasi seperti interleukin 10 yang nyata berkurang. [14]

Interleukin 1 memiliki peran dalam modulasi ekspresi metalloproteinase. [13] Disparitas antara proteinase dan aktivitas inhibitor proteinase juga telah dipastikan [15] dan dapat menyebabkan degradasi stroma kornea; sebagai temuan patologis utama di KC. Telah ditemukan bahwa pada mata keratoconic, proteinase inhibitor seperti 2-macroglobulin dan 1-antiprotease secara signifikan berkurang dari mata yang normal [16] dan aktivitas yang lebih tinggi dari lisosomal dan enzim katabolik seperti proteinase telah dilaporkan. [17]

DiagnosaDiagnosa KC ditegakkan dari pemeriksaan slit lamp, pemeriksaan klinis dan pencitraan topografi kornea. Pada pemeriksaan slit lamp, didapatkan adanya penonjolan sel kerucut kornea, Vogt striae, cincin Fleischer, tanda Munson, tanda Rizzuti, bekas luka kornea dan refleks scissoring oleh retinoscopy.

Keratoconus dan Dasar GenetikMeskipun penyakit ini sebagian besar termasuk dominan autosomal herediter, namun kasus KC dapat muncul secara sporadis dan poligenik. [23] Fenomena genetik yang kompleks membuat identifikasi gen penyebab menjadi sulit. Salah satu strategi untuk mengalokasikan gen penyebabnya adalah analisis linkage. Pertama perlu dilakukan identifikasi daerah mana dari kromosom yang terkena yang mungkin gen penyebab. Setelah mendefinisikan wilayah kromosom, gen dipetakan dengan wilayah yang akan diklarifikasi. [36], [37], [38], [39]Gen VSX1 yang pertama kali ditemukan pada tahun 2002, [46] adalah gen homeoboks yang mengikat wilayah kontrol merah / hijau pigmen penglihatan cluster gen dan berperan untuk mengatur ekspresi kerucut opsin. Mutasi yang berbeda dari gen ini telah diidentifikasi dalam beberapa perkembangan anomali endotelium bersama dengan beberapa keluarga dengan KC [46], [47], [48], [49] [50] pada 80 pasien keratoconic, VSX1 disimpulkan menjadi gen penting dalam autosomal dominan KC. Gen kandidat lain yang menarik bagi para peneliti dalam patogenesis KC adalah SOD1 pada kromosom 21. [58]

Cornea, a Good Candidate for Gene Therapy Past and Future

Corneal gene therapy as a powerful method that can modify the ultrastructure of the cell protein is potentially helpful in many of hereditary and acquired corneal abnormalities.

In 1994, Mashhour et al. transferred successfully gene to the cornea with the application of adenovirus as a vector. [59] Since then, new aspects were recognized for this apparatus. Transferring cytokines, growth factors and enzymes to the cornea in a sustained concentration that is hardly if at all achievable with systemic administration along with knock down of defective genes and inducing the functional genes are only part of the presumed advantages. [60],[61]

In preclinical studies, outstanding results for this method have been obtained. Researchers found promising results in the prevention and treatment of major corneal issues like herpetic stromal keratitis (HSK), corneal graft rejection, neovascularization and haze. [61],[62],[63],[64],[65],[66] This method has also been postulated for other corneal abnormality like KC [67] and corneal dystrophies. [68],[69]

There are lots of intrinsic characters that make the cornea an ideal candidate for gene therapy. One of these important characters is the exceptional policy of the immune system towards this tissue in comparison to others, the so-called immune privilege.

Excessive inflammation that is considered to be a very useful strategy against microorganism and is one of the routine immune response to combat the offending enemy is extremely harmful to cornea. This inflammation easily causes opacities in the cornea that affects the vision significantly.

The margination of the inflammatory cells is restricted by a blood ocular barrier. Even after entrance the activity of these cells becomes suspiciously inhibited. Endothelial cells express molecules that inhibit complement activation and subsequently the opsonization and destructive effect of the complement cascade. Presenting the antigens to immune cells is also modified in this tissue and corneal cells express comparatively lower histocompatibility complex of both classes (I and II). Lymphatic drainage as a pathway to present the antigens to dendritic cells in lymph nodes are lacking as well and fas ligands that are presented on the surface of the corneal cells induce apoptosis in activated T cells And for reasons that are poorly understood, presenting B cells do not secrete complement fixating immunoglobulins M and immunoglobulins G2. [70],[71]

These features give a unique property to the cornea for accommodating the gene vectors without consequent immunogenicity and thus will guarantees longer gene expression.

Other properties like the stability ex vivo are particularly of significant importance. [64],[72] This feature makes the successful manipulation for gene therapy out of the body possible.

Easily accessible [64],[72],[73],[74] and anesthetized [75] along with transparency, [64],[65],[72] which makes direct observation of the procedure progress effortless, are other technical facilities that this tissue offers to ophthalmologists.

Technique

Basics of the techniques are the same as gene therapy in other tissues. Gene that its downstream products are desirable is transferred to an appropriate vector. The vector is then injected into the tissue in a particular way to obtain and enter the target cell and with the application of the protein synthesis machinery of the cell, gene translation starts.

An optimal vector must suit for the purpose of the gene therapy and a property that is essential for one vector might be useless and even harmful for another. However as a rule, the less immunogenic be a vector, the better. Besides, vectors that can carry larger sequence are often preferred under equal condition, and the ability to express both in proliferative and non-proliferative cells is another functional feature.

At the present time, there are viral and non-viral vectors. Adenovirus, Herpes simplex virus, Lentiviruses, Retroviruses and Adeno-associated virus is among the most popular viral vectors [76],[77],[],[78],[79],[80],[81] and Naked DNA, Cationic liposomes, Minimalistic immunologically defined gene expression vectors as well as Polyethylenimines and Polyamidoamine dendrimers are among the non-viral biologic methods. [81],[82],[83]

Physical methods have also moved forward and progressed in recent years. Electroporation, Sonoporation and Gene gun have been utilized with real success. [84],[85],[86],[87],[88]

Details of vectors and physical methods are beyond the scope of this paper.

Conclusion

Excessive body of documents indicates the role of genes in the pathogenesis of KC and further investigations are to complete this complex puzzle. As discussed above, despite a very comprehensive genetic analysis, no single gene was discovered as the disease causing gene. And to the time of finding the gene (s), despite progress in gene delivery and control of the microenvironment of the cornea, the application of gene therapy in the treatment of the KC remains in future prospect.

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