Faydalı Mutasiya varmı?

84
  CCR5 Genindəki Faydalı Mutasiya 
 
 2001-ci ildə edilən bir araşdırmanın nəticəsinə görə, insanlarda olan CCR5 adlı bir gendə meydana gələn 32 kodun delasiyası (silinməsi) zamanı, bu gen baxımından homoziqot fərdlərdə HİV müqaviməti, heteroziqotlarda isə HİV əlamətlərinin ortaya çıxmasında gecikmə meydana gəldiyi müşahidə edilmişdir.

   CCR5-Δ32 gen sahəsindəki mutasiya HİV-ə keçişi yavaşladar və eyni gendə reallaşan iki mutasiya isə bir kimsənin HİV infeksiyasına qarşı müqavimətini daha da artırır. Böyük bir təkamül təcrübəsinin içində yaşayırıq. Gözlərimizin qarşısında təkamül keçirməkdə olan insan vardır. HİV deyilən virus, 19-cu əsrdə bilinməyən, ancaq indi tam da olmasa çox öyrənilmiş bir virusdur. Təkamül əleyhdarları üçün belə, HİV-ə qarşı immunitetin yaranması dəyişərək törəmənin dəlilidir, çünki bu prosesin reallaşmasına asanlıqla şahid olurlar. 

Mövzumuz insandakı bir genin məruz qaldığı mutasiyadır. CC kemokin reseptor 5 (CCR5), insanlarda CCR5 geni ilə kodlanmış bir zülaldır. CCR5, güclü olaraq T-killer (Timus limfositləri) hüceyrələrində, makrofaqlarda, dendritik hüceyrələrdə və mikroqliada təsir göstərir. Bu genin insandakı iltihabın qarşısının alınmasında rol oynadığı düşünülür.
Bəzi populyasiyalar, Delta32 mutasiyasını qazanmışdır, ki bu mutasiya CCR5 genindeki genetik məlumatın bir qisminin silinməsinə səbəb olmuşdur (32-bp seqment silinməsi). Bu mutasiyasını daşıyan homozigot fərdlər, HİV infeksiyasına qarşı tamamilə ya da qismən müqavimətlidir (yuxarıda söylədiyimiz kimi, homoziqot və heterozigot olmasına görə dəyişər).
HİV, hücum  zamanı hüceyrələrə girmək üçün bir ön qəbuledici (reseptor) olaraq əksəriyyətlə CCR5 və ya CXCR4 zülallarını istifadə edir. Delta32 mutasiyası baş verdikdə isə, qəbuledici işləməz hala gəldiyi üçün HİV virusunun tutunması və hüceyrəyə girməsinə maneə törədilir, bu alel genlərdən 2 nüsxədə olması, HİV üçün daha da yüksək bir müqavimət meydana gətirir. Bu alel, Avropalıların  5-14 

%ində tapılır, Afrika və Asiyada isə çox nadir hallarda rast gəlmək olur. Bir çox insanlarda, yalnız bir allelin varlığının belə, HİV daşıyıcısı kəslərdə AİDS xəstəliyinin meydana gəlməsinin 2 il gecikdirdiyini göstərir. Bu da xeyrli mütasiyalara göstəriləcək sübutlardan biridir. Genetik analizlər əziyyətli və bahalı olduğu üçün bu sahədə daha çox işlərin görülməsi ləngəyir.

 
Mutasiyanın Tibbdə Əhəmiyyəti
 
Son zamanlarda isə kliniki eksperimentlər insanda immunçatışmazlığı virusuna  qarşı gen terapiyası effektivliyini təsdiq etdi. Bunun üçün sadəcə immun hüceyrələrindəki genlərdən birinin fəaliyyətini dəqiqliklə dayandırmaq kifayətdir.
 
“Bunu “berlin pasienti” Timoti Braun’un dövründən bəri QİÇS-in müalicəsindəki ilk ciddi sıcrayış adlandırmaq olar”, – Kaliforniya Universitetindən olan bioloq John Rossi qeyd edir.
 
Bioloq 2008-ci ilin, hətta bəlkə bütün dövrlərin ən məşhur tibbi hadisəsini xatırladır. Həmin vaxt Braun üzərində eksperimental kök hüceyrə terapiyası uğurla aparılmışdı. Ona, mutasiyaya uğramış CCR5 geni olan donordan hematopoetik hüceyrələr transplantasiya edilmişdi. Onların kodlaşdırdığı zülal HİV-nin insanın T-limfositlərinə yoluxmasında maneə meydana gətirmişdir. CCR5 çatışmazlığı olan insan isə bu prosesdə HİV-ə qarşı güclü müqavimət qazanmış olur. Braun, ona tətbiq edilmiş antivirus terapiyasından sonra uğurla sağaldılmışdı.

Buna baxmayaraq kök hüceyrələri ilə terapiya üsulu əksər İİV-yə yoluxmuş insanlar üçün əlverişsizdir. Bu, ağır invaziv prosedurdur və donor hüceyrələrin ayrılma riski yenə də yüksək olaraq qalır. Elə isə mutasiyalı CCR5-i xəstənin öz hüceyrələrinə əlavə etdikdə üstünlüyünü necə qoruyub saxlamaq olar? Alimlərdən ibarət bir beynəlxalq qrup bu mutasiyanı birbaşa xəstənin öz hüceyrələrində istifadə etmək qərarına gəldi.
 
 

Nature jurnalında dərc edilən məqalədə infeksiyanı nəzarət altında saxlamaq üçün davamlı antiretrovirus vasitələri qəbul edən 12 könüllü HİV xəstəsi üzərində aparılmış tədqiqatdan bəhs edilir. Könüllülərin qanlarından HİV-nin məhv etdiyi immun limfosit-hüceyələri ayırd edildi və “zink barmaqlar” (zinc finger) fermentləri ilə müalicə edildi, hansılar ki DNT ilə verilmiş hissədə birləşərək müvafiq genin aktivliyini nizamlayır. Effekti əhəmiyyətli oldu: xəstələrin qanlarındaki T-limfositlərin səviyyəsi artdı, bu da virusun yoluxma və məhv etmə bacarığının sürətlə azaldığından xəbər verir.
Nəticələr aydın olduqdan sonra tədqiqatda iştirak edən xəstələrin yarısına antiretrovirus preparatları qəbulu dayandırıldı, qandaki T-limfositləri və virus hissəcikləri məzmununun izlənilməsi prosesi isə davam etdirildi. Hətta bu vəziyyətdə belə İİV səviyyəsi daha zəif artır və limfosit səviyyəsi növbəti bir neçə həftə ərzində yüksək olaraq qalırdı. Başqa deyimlə, virus tərəfindən məhv edilməyən mutasiyalı limfositlər özlərini xəstələrin orqanizmində çox yaxşı hiss edirdilər. Alimlər xoşagəlməz qoxudan başqa heç bir əlavə təsirin meydana gəlmədiyini qeyd etdilər.

 
Hazırlayan: Hikmət Həmdullayev

Mənbə:
1) Həyatın Təkamülü
2) Evrim Ağacı
3) Tibbi Biologiya və Genetikanın Əsasları (2008, Bakı)
PAYLAŞ
Öncəki yazıHəyatın var olduğu düşünülən planet
Sonrakı yazıHiggs Bozonu

AZƏRBAYCAN TİBB UNİVERSİTETİNDƏ TƏHSİL ALIR. ƏSASƏN FƏLSƏFƏ,PSİXATRİYA/PSİXOLOGİYA,TİBB BÖLMƏSİNDƏ MƏQALƏLƏR YAZIR. REZONANSIN İDEYA MÜƏLLİFİDİR.

84 ŞƏRH

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