Roles and Mechanisms of Astragaloside IV in Combating Neuronal Aging.

Aging can lead to changes in the cellular milieu of the brain. These changes may exacerbate, resulting in pathological phenomena (including impaired bioenergetics, aberrant neurotransmission, compromised resilience and neuroplasticity, mitochondrial dysfunction, and the generation of free radicals) and the onset of neurodegenerative diseases. Furthermore, alterations in the energy-sensing pathways can accelerate neuronal aging but the exact mechanism of neural aging is still elusive. In recent decades, the use of plant-derived compounds, including astragaloside IV, to treat neuronal aging and its associated diseases has been extensively investigated. This article presents the current understanding of the roles and mechanisms of astragaloside IV in combating neuronal aging. The ability of the agent to suppress oxidative stress, to attenuate inflammatory responses and to maintain mitochondrial integrity will be discussed. Important challenges to be tacked for further development of astragaloside IV-based pharmacophores will be highlighted for future research.

Novel Loss-of-Function Mutations in DNAH1 Displayed Different Phenotypic Spectrum in Humans and Mice.

Male infertility is a prevalent disorder distressing an estimated 70 million people worldwide. Despite continued progress in understanding the causes of male infertility, idiopathic sperm abnormalities such as multiple morphological abnormalities of sperm flagella (MMAF) still account for about 30% of male infertility. Recurrent mutations in DNAH1 have been reported to cause MMAF in various populations, but the underlying mechanism is still poorly explored. This study investigated the MMAF phenotype of two extended consanguineous Pakistani families without manifesting primary ciliary dyskinesia symptoms. The transmission electron microscopy analysis of cross-sections of microtubule doublets revealed a missing central singlet of microtubules and a disorganized fibrous sheath. SPAG6 staining, a marker generally used to check the integration of microtubules of central pair, further confirmed the disruption of central pair in the spermatozoa of patients. Thus, whole-exome sequencing (WES) was performed, and WES analysis identified two novel mutations in the DNAH1 gene that were recessively co-segregating with MMAF phenotype in both families. To mechanistically study the impact of identified mutation, we generated Dnah1 mice models to confirm the in vivo effects of identified mutations. Though Dnah1△iso1/△iso1 mutant mice represented MMAF phenotype, no significant defects were observed in the ultrastructure of mutant mice spermatozoa. Interestingly, we found DNAH1 isoform2 in Dnah1△iso1/△iso1 mutant mice that may be mediating the formation of normal ultrastructure in the absence of full-length protein. Altogether we are first reporting the possible explanation of inconsistency between mouse and human DNAH1 mutant phenotypes, which will pave the way for further understanding of the underlying pathophysiological mechanism of MMAF.

Homozygous mutations in C14orf39/SIX6OS1 cause non-obstructive azoospermia and premature ovarian insufficiency in humans.

Human infertility is a multifactorial disease that affects 8%-12% of reproductive-aged couples worldwide. However, the genetic causes of human infertility are still poorly understood. Synaptonemal complex (SC) is a conserved tripartite structure that holds homologous chromosomes together and plays an indispensable role in the meiotic progression. Here, we identified three homozygous mutations in the SC coding gene C14orf39/SIX6OS1 in infertile individuals from different ethnic populations by whole-exome sequencing (WES). These mutations include a frameshift mutation (c.204_205del [p.His68Glnfs∗2]) from a consanguineous Pakistani family with two males suffering from non-obstructive azoospermia (NOA) and one female diagnosed with premature ovarian insufficiency (POI) as well as a nonsense mutation (c.958G>T [p.Glu320∗]) and a splicing mutation (c.1180-3C>G) in two unrelated Chinese men (individual P3907 and individual P6032, respectively) with meiotic arrest. Mutations in C14orf39 resulted in truncated proteins that retained SYCE1 binding but exhibited impaired polycomplex formation between C14ORF39 and SYCE1. Further cytological analyses of meiosis in germ cells revealed that the affected familial males with the C14orf39 frameshift mutation displayed complete asynapsis between homologous chromosomes, while the affected Chinese men carrying the nonsense or splicing mutation showed incomplete synapsis. The phenotypes of NOA and POI in affected individuals were well recapitulated by Six6os1 mutant mice carrying an analogous mutation. Collectively, our findings in humans and mice highlight the conserved role of C14ORF39/SIX6OS1 in SC assembly and indicate that the homozygous mutations in C14orf39/SIX6OS1 described here are responsible for infertility of these affected individuals, thus expanding our understanding of the genetic basis of human infertility.

Exonuclease 5 is dispensable for meiotic progression and male fertility in mouse.

Exonuclease 5 (Exo5) belongs to a class of bi-directional, ssDNA-specific exonucleases that mainly involved in the DNA repair pathways. Exo5 has been reported to be crucial for DNA- DNA mismatch repair (MMR) in several human cell lines. However, its in vivo function in mammals still needs to be explored. Thus, to study the in vivo role of Exo5 in spermatogenesis, Exo5 knockout mice were generated using CRISPR/Cas9 technology. Unexpectedly, we found that the knockout mice are fertile despite a slight decrease in sperm count. Furthermore, Exo5-/- mice showed no detectable developmental anomalies, exhibited no remarkable differences in the epididymal histology and testis/body weight ratio. Moreover, cytological investigations on meiocytes revealed non-significant differences in chromosomal synapsis, recombination, and meiotic progression of prophase I, further demonstrating that Exo5 has no essential role in spermatogenesis in mice under normal breeding conditions. Collectively, these data indicate that Exo5 is dispensable for meiotic progression and fertility in mice.

A TOP6BL mutation abolishes meiotic DNA double-strand break formation and causes human infertility.

Meiosis is pivotal for sexual reproduction and fertility. Meiotic programmed DNA double-strand breaks (DSBs) initiate homologous recombination, ensuring faithful chromosome segregation and generation of gametes. However, few studies have focused on meiotic DSB formation in human reproduction. Here, we report four infertile siblings born to a consanguineous marriage, with three brothers suffering from non-obstructive azoospermia and one sister suffering from unexplained infertility with normal menstrual cycles and normal ovary sizes with follicular activity. An autosomal recessive mutation in TOP6BL was found co-segregating with infertility in this family. Investigation of one male patient revealed failure in programmed meiotic DSB formation and meiotic arrest prior to pachytene stage of prophase I. Mouse models carrying similar mutations to that in patients recapitulated the spermatogenic abnormalities of the patient. Pathogenicity of the mutation in the female patient was supported by observations in mice that meiotic programmed DSBs failed to form in mutant oocytes and oocyte maturation failure due to absence of meiotic recombination. Our study thus illustrates the phenotypical characteristics and the genotype-phenotype correlations of meiotic DSB formation failure in humans.