兒童睡眠呼吸中止症的特定基因表現增加
作者：Robert Lowes
出處：WebMD醫學新聞
February 10, 2010 — 一項新研究顯示，一個基因編碼磷酸絲氨酸磷酸分解酶，PSPH，在罹患睡眠呼吸中止症（OSA）兒童扁桃腺中的表現增加。抑制PSPH降低淋巴球增生且增加細胞死亡，可以作為罹患OSA兒童一個非手術的治療選擇。
這項由芝加哥大學與路易維耳市大學兒童睡眠研究中心合作的研究，線上發表於1月21日的美國呼吸與重症醫學期刊。
OSA影響高達3%的兒童族群，且與代謝、心臟以及神經認知疾病有關。雖然研究已經證實暴露在吸菸、過敏、以及呼吸系統感染（RIs）可能都與扁桃腺上皮過度增生有關，但這個機轉目前仍然未知。罹患OSA兒童病患經常接受的治療是外科切除扁桃腺以及腺狀腫，隨之而來的是風險、疼痛與費用。
資深作者伊利諾州芝加哥大學兒科部的David Gozal醫師在電子郵件中向Medscape胸腔醫學表示，我們對於為什麼以及扁桃體腺樣體組織如何生理性與病理性地生長仍然知道的不多。內在免疫與呼吸道結構決定因素，可能在沒有任何其他因素下促使扁桃體腺樣體組織生長。他指出，有趣的是，相當數量的兒童在沒有發生OSA的情況下，扁桃腺感染再發。
科羅拉多州奧羅拉健康科學中心以及科羅拉多州立大學兒童醫院的Ann C. Halbower醫師致電給Medscape胸腔醫學時評論，無疑的，我們看到經常過敏或是感染的兒童們並不會罹患長期扁桃體腺樣體組織過度增生。相反的反而是更常見的，那些經常有呼吸相關問題的兒童，扁桃腺與腺體較大，很顯然地，過敏與對扁桃腺體的效應是有基因傾向的。
這項研究一開始的測試族群包括6~11歲的兒童，於開刀前確認並收納，他們在Kosair兒童醫院接受扁桃腺切除。這18位OSA病患是連續的、非肥胖病患，在路易維耳市中心接受多導睡眠圖測試，且受邀參與這項研究。另一組年齡、性別與種族相符的比較組，包括18位經常罹患RI（在6個月內至少有5次扁桃腺感染且需要使用抗生素），但是沒有睡眠異常的兒童。
這36位兒童的扁桃腺體都以RNA微陣列分析，接著以基因組增強分析找出OSA組織中富含的基因組。總共分析了1880條途徑，OSA組織中總共富含22項基因組，但是在RI組，這些基因組並未增加。這些表現較強的基因組可以分為幾種功能性分類，其中最多的是牽涉到增生的基因組（共564個基因）。
相連性與不同表現的複雜性分析將這個範圍縮小到69個基因，包括一些牽涉到調控、發炎訊息、或是組織生長的基因。研究者們追蹤兩種統計上顯著網絡基因組，分別是DUSP1與PSPH，這兩個基因組都編碼蛋白磷酸分解酶。扁桃腺組織培養免疫組織化學檢驗顯示PSPH蛋白表現侷限在淋巴結的生長中心（germinal center），且在OSA組織的表現比RI組織高。
以漸增濃度的蛋白磷酸分解酶抑制劑okadaic acid或是calyculin A處理培養組織，相較於控制組病患，來自OSA病患產生濃度依賴性培養組織細胞增生下降的現象（總數為6個）（三種濃度的okadaic acid濃度的P值都小於0.05；以calyculin A而言，P值小於0.1）。來自RI病患的組織，這些抑制劑對培養組織的影響（總數為6個）則是未達顯著差異。
回顧OSA兒童病患的非外科治療，作者們引用研究顯示剃除PSPH基因表現的老鼠抑制了神經幹細胞的複製。PSPH基因缺陷兒童的單一病例牽涉到生長與精神運動功能遲滯，以及面部異常，除此之外，淋巴母細胞與纖維母細胞的PSPH活性也都是下降的。因此，全身性地抑制PSPH顯然是不適當的。
Gozal醫師表示，抑制PSPH或剔除的主意將會發明出選擇性標的運送系統，例如微脂粒組成噴霧或是其他形式的藥物運載微粒，可以局部性地投予至受影響組織，而不會到達全身。他附帶表示，很可能可以研發其他策略來選擇性地抑制藥物/siRNA/其他基因剃除方式專一地作用於扁桃腺與腺上皮組織內的細胞。
麻州波士頓哈佛醫學院神經科副教授、兒童醫院兒童睡眠異常中心副主任Sanjeev V. Kothare醫師透過電子郵件向Medscape胸腔醫學評論，現在需要臨床研究來看標的治療對於PSPH的作用，看是否僅抑制扁桃體腺樣體異常增生，還是也會造成正常幹細胞複製的傷害。Kothare醫師表示，另一個問題是，使用這些針對PSPH藥物的最佳年齡。
Gozal醫師的結論是，起始研究確實證實了這個觀念。需要更多的研究來確認應該針對哪個或哪些基因，或許合併起來會有更好的效果。
Gozal醫師、Kothare醫師與Halbower醫師表示沒有相關資金上的往來。
Gene Upregulated in Pediatric Obstructive Sleep Apnea
By Robert Lowes
Medscape Medical News
February 10, 2010 — A new study has found that a gene coding for phosphoserine phosphatase, PSPH, is upregulated in the tonsils of children with obstructive sleep apnea (OSA). Inhibition of PSPH reduces lymphocyte proliferation and increases cell death, suggesting strategies for nonsurgical therapy in children with OSA.
The University of Chicago study, carried out in collaboration with the University of Louisville Pediatric Sleep Research Center, was published online January 21 in the American Journal of Respiratory and Critical Care Medicine.
OSA affects up to 3% of the pediatric population and is associated with metabolic, cardiovascular, and neurocognitive illnesses. Although studies have shown that exposure to smoking, allergies, and respiratory infections (RIs) may contribute to adenotonsillar hypertrophy, the mechanisms are not well understood. The usual treatment for children with OSA is surgical removal of tonsils and adenoids, with the attendant risk, pain, and expense.
"We are remarkably ignorant to this day as to why and how adenotonsillar tissues grow both physiologically and pathologically," senior author David Gozal, MD, from the Department of Pediatrics at the University of Chicago, Illinois, writes in an email to Medscape Pulmonary Medicine. "It is definitely possible that intrinsic immunologic and airway structural determinants may promote the growth of adenotonsillar tissues in the absence of all other factors." He pointed out that, interestingly, a sizable population of children experience recurring tonsillar infections without developing OSA.
"Certainly we've seen children who have frequent allergies or frequent infections that don't get long-term adenotonsillar hypertrophy," commented Ann C. Halbower, MD, from the Department of Pediatrics and the Children's Hospital Sleep Center, The Children's Hospital and University of Colorado, Denver, Health Sciences Center, Aurora, Colorado, by telephone to Medscape Pulmonary Medicine. "However the opposite is probably seen more often — those who have frequent respiratory issues do have large tonsils and adenoids...it seems quite apparent that there may be a genetic predisposition for both allergies and an effect on the tonsils," she noted.
The initial test population in this study consisted of children 6 to 11 years old, identified and recruited before surgery, undergoing tonsillectomies at Kosair Children's Hospital. The 18 OSA patients were consecutive, nonobese patients diagnosed at the Louisville center by polysomnographic testing and invited to participate. A comparison group matched by age, sex, and ethnicity consisted of 18 children with frequent RIs (at least 5 tonsillar infections in 6 months requiring antibiotics) but no sleep disorders.
Microarray RNA analysis of tonsillar tissue from all 36 children was followed by gene set enrichment analysis to identify gene sets enriched in OSA tissue. Of 1800 pathways investigated, 22 gene sets were enriched in OSA tissue, but none in RI tissue. Enriched gene sets fell into several functional categories, with genes involved in proliferation being the most numerous (564 genes).
Complex analyses of connectivity and differential expression narrowed the field to 69 genes, including some involved in regulation, inflammation signaling, or tissue growth. Investigators followed up on 2 of the "statistically significant network genes," DUSP1 and PSPH, both coding for protein phosphatases. Immunohistochemistry of tonsillar tissue cultures showed that PSPH protein expression localized in germinal centers and was more abundant in OSA than RI cultures.
Treating the cultures with increasing concentrations of protein phosphatase inhibitors okadaic acid or calyculin A produced concentration-dependent decreases in cell proliferation in cultures (n = 6) from OSA patients compared with control patients (for all 3 concentrations of okadaic acid, P < .05; for all 3 concentrations of calyculin A, P < .01). Effects of these inhibitors on cultures (n = 6) from patients with RIs were nonsignificant.
Thinking ahead to nonsurgical therapies for pediatric OSA, the authors cite studies showing that knockdown of PSPH expression in mice inhibited proliferation of neural stem cells. A single case of PSPH deficiency reported in a child involved growth and psychomotor retardation and facial abnormalities, as well as decreased PSPH activity in lymphoblasts and fibroblasts. Thus, systemic inhibition of PSPH would obviously be inappropriate.
"The idea for PSPH inhibition or knockdown would be to devise selective targeted delivery systems such as a liposome construct spray or other types of drug delivery vehicles that could be delivered locally to the affected tissues without going the systemic route," said Dr. Gozal. "It is possible that other strategies could be developed to selectively limit the drug/siRNA/other knockdown method to specific cells within the tonsils and adenoids," he added.
Sanjeev V. Kothare, MD, associate director, Center for Pediatric Sleep Disorders, Children's Hospital, and associate professor, Department of Neurology, Harvard Medical School, Boston, Massachusetts, commented by email to Medscape Pulmonary Medicine that clinical studies will be needed to see the effect of targeted therapy on PSPH, whether it not only inhibits adenotonsillar hypertrophy but causes other damage to normal stem cell proliferation. "Another issue is at what age to use these agents to target PSPH," noted Dr. Kothare.
"This initial work is really a demonstration of proof of concept," Dr. Gozal concluded. "Much work needs to be done to identify which gene or genes should be targeted, maybe in combination, to achieve the desired results."
Dr Gozal, Dr. Kothare, and Dr. Halbower have disclosed no relevant financial relationships.
Am J Respir Crit Care Med. Published online January 21, 2010.
