Meiosis In Cryptococcal Infection

摘要 真菌病原体新生隐球菌造成50多万人死亡 在世界范围内，每年主要是因为艾滋病大流行。流行病学证据表明， 无症状隐球菌感染在普通人群中的流行率。致命的全身性疾病 通常通过重新激活患者的潜伏感染而发生，当患者的免疫力因艾滋病毒感染而受损时 或者免疫抑制疗法。尽管隐球菌通常以单倍体状态生长，但大型多倍体 在感染的肺部观察到隐球菌细胞(主要是4C细胞，偶尔是8C细胞)，并被建议 促进隐球菌潜伏期和持久性。这些多倍体细胞随后可以产生小的 单倍体隐球菌群。目前尚不清楚隐球菌体在感染过程中如何发生倍性降低。 以及这一过程是否有助于隐球菌的重新激活。 我们的初步数据显示，血清中隐球菌细胞亚群随着 减数分裂突变体显示细胞大小增加的细胞比例增加。有趣的是，我们发现 基因毒性应激诱导的多倍体隐球菌细胞在脱毒过程中表现出减数分裂样特征 体外多倍化过程。一直以来，阻止减数分裂会阻碍体外倍性的减少。减数分裂 与野生型相比，当多倍体细胞被 用来给老鼠接种疫苗。最令人兴奋的是，我们发现减数分裂特异重组酶基因DMC1是 在隐球菌病的小鼠模型中，在感染期间在隐球菌中激活。这些初步数据导致 美国假设隐球菌可以通过多倍化来响应恶劣的寄主环境，这 由于HIV感染，真菌可以在允许的寄主条件下通过减数分裂恢复正常倍性， 产生增殖性单倍体后代并引起致命的全身感染。因此，关联的生命周期 隐球菌病的进展可能类似于癌症的配子发生过程。在这个过程中， 各种癌细胞对基因毒性化疗或放射治疗的反应会变成多倍体。这些 多倍体肿瘤细胞可以通过类似减数分裂的过程去多倍化，产生年轻的和 倍体正常的增殖性癌细胞。在这个探索性的R21提案中，我们的目标是确定 感染过程中隐球菌减数分裂的发生(目标1)，并对倍性过程进行剖析 减少这种病原体，并评估减数分裂对隐球菌致病的贡献(目标2)。这个 拟议的工作是进一步全面调查重要而又糟糕的 了解隐球菌疾病进展的各个方面(潜伏期和重新激活)。

ABSTRACT The fungal pathogen Cryptococcus neoformans is responsible for more than half a million deaths worldwide each year largely because of the AIDS pandemic. Epidemiological evidence indicates a high prevalence of non-symptomatic cryptococcal infections in the general population. Fatal systemic diseases often occur through re-activation of latent infections in patients when their immunity is impaired by HIV infection or immunosuppressive therapies. Although Cryptococcus typically grows in a haploid state, large polyploid Cryptococcus cells (mostly 4C and occasionally 8C) are observed in infected lungs and are proposed to promote cryptococcal latency and persistence. These polyploid cells can subsequently give rise to small haploid cryptococcal populations. It is unclear how ploidy reduction occurs in Cryptococcus during infection and whether this process contributes to Cryptococcus reactivation. Our preliminary data indicate that a subpopulation of Cryptococcus cells become large in serum with meiosis mutants showing increased proportion of cells with elevated cell size. Interestingly, we found that large polyploid cryptococcal cells induced by genotoxic stress showed meiosis-like features during de- polyploidization process in vitro. Consistently, blocking meiosis impedes ploidy reduction in vitro. The meiosis mutants also showed reduced fungal burden in the lungs compared to the wild type when polyploid cells were used to inoculate mice. Most excitingly, we found that the meiosis-specific recombinase gene DMC1 is activated in Cryptococcus during infection in the murine model of cryptococcosis. These preliminary data led us to hypothesize that Cryptococcus can respond to the hostile host environment by polyploidization and this fungus can return to normal ploidy through meiosis in a permissive host condition due to HIV infection, generating proliferative haploid progeny and causing fatal systemic infections. Thus the life-cycle associated progression of cryptococcosis might be similar to the gametogenesis process of cancer. In that process, various cancer cells become polyploid in response to genotoxic chemotherapy or radiation therapy. These polyploid tumor cells can de-polyploidize through a meiosis-like process, giving rise to rejuvenated and proliferative cancer cells with normal ploidy. In this exploratory R21 proposal, our objectives are to determine the occurrence of meiosis in Cryptococcus during infection (Aim 1), and to dissect the process of ploidy reduction in this pathogen and to assess the contribution of meiosis to cryptococcal pathogenesis (Aim 2). The proposed work is a stepping stone for further comprehensive investigation into the important and yet poorly understood aspects of cryptococcal disease progression (latency and reactivation).