The Complicated Nature of Somatic mtDNA Mutations in Aging

Mitochondria are the main source of energy used to maintain cellular homeostasis. This aspect of mitochondrial biology underlies their putative role in age-associated tissue dysfunction. Proper functioning of the electron transport chain (ETC), which is partially encoded by the extra-nuclear mitochondrial genome (mtDNA), is key to maintaining this energy production. The acquisition of de novo somatic mutations that interrupt the function of the ETC have long been associated with aging and common diseases of the elderly. Yet, despite over 30 years of study, the exact role(s) mtDNA mutations play in driving aging and its associated pathologies remains under considerable debate. Furthermore, even fundamental aspects of age-related mtDNA mutagenesis, such as when mutations arise during aging, where and how often they occur across tissues, and the specific mechanisms that give rise to them, remain poorly understood. In this review, we address the current understanding of the somatic mtDNA mutations, with an emphasis of when, where, and how these mutations arise during aging. Additionally, we highlight current limitations in our knowledge and critically evaluate the controversies stemming from these limitations. Lastly, we highlight new and emerging technologies that offer potential ways forward in increasing our understanding of somatic mtDNA mutagenesis in the aging process.

A Semi-Quantitative Assay to Measure Glycosaminoglycan Degradation by the Urinary Microbiota

Glycosaminoglycans (GAGs) are linear polysaccharides and are among the primary components of mucosal surfaces in mammalian systems. The GAG layer lining the mucosal surface of the urinary tract is thought to play a critical role in urinary tract homeostasis and provide a barrier against urinary tract infection (UTI). This key component of the host-microbe interface may serve as a scaffolding site or a nutrient source for the urinary microbiota or invading pathogens, but its exact role in UTI pathogenesis is unclear. Although members of the gut microbiota have been shown to degrade GAGs, the utilization and degradation of GAGs by the urinary microbiota or uropathogens had not been investigated. In this study, we developed an in vitro plate-based assay to measure GAG degradation and utilization and used this assay to screen a library of 37 urinary bacterial isolates representing both urinary microbiota and uropathogenic species. This novel assay is more rapid, inexpensive, and quantitative compared to previously developed assays, and can measure three of the major classes of human GAGs. Our findings demonstrate that this assay captures the well-characterized ability of Streptococcus agalactiae to degrade hyaluronic acid and partially degrade chondroitin sulfate. Additionally, we present the first known report of chondroitin sulfate degradation by Proteus mirabilis, an important uropathogen and a causative agent of acute, recurrent, and catheter-associated urinary tract infections (CAUTI). In contrast, we observed that uropathogenic Escherichia coli (UPEC) and members of the urinary microbiota, including lactobacilli, were unable to degrade GAGs.

Optogenetic scrambling of hippocampal theta oscillations alters working memory retrieval but not hippocampal spatiotemporal codes

The precise temporal coordination of activity in the brain is thought to be fundamental for memory encoding and retrieval. The medial septum (MS) provides the largest source of innervation to the hippocampus (HPC), and its inhibitory neurons play a major role in controlling HPC theta (~8 Hz) oscillations. While pharmacological inhibition of the MS is associated with memory impairment, the exact role of MS inhibitory neurons in HPC function and memory is not fully understood. While HPC place cells were previously reported to not depend on MS inputs, the exact role of MS inputs on HPC temporal codes is still a matter of debate. Moreover, pharmacological manipulations do not have the temporal resolution to distinguish the role of MS activity on working memory encoding, retention and retrieval. Here we stimulated the MS with optogenetics to either pace or ablate theta, while recording large hippocampal assemblies over time using calcium imaging along with local field potentials to monitor theta control. Using scrambled light stimulation, we could robustly ablate theta signals, which was associated with direct modulation of a subpopulation of neurons in the HPC. We found that such stimulation led to decreased working memory retrieval, but not encoding in both a delayed non-match to sample task and a novel place object recognition task. Strikingly, scrambled stimulations were not associated with disrupted spatiotemporal codes. Importantly, we show that our opsin did not transfect cholinergic cells and stimulation did not disrupt HPC ripple activity or running speed, suggesting a specific role for MS GABAergic cells in memory maintenance and retrieval that is independent from these other potential confounding mechanisms. Our study suggests that theta signals play a specific and essential role in supporting working memory retrieval and maintenance while not being necessary for hippocampal spatiotemporal codes.

Ebf Activates Expression of a Cholinergic Locus in a Multipolar Motor Ganglion Interneuron Subtype in Ciona

Conserved transcription factors termed “terminal selectors” regulate neuronal sub-type specification and differentiation through combinatorial transcriptional regulation of terminal differentiation genes. The unique combinations of terminal differentiation gene products in turn contribute to the functional identities of each neuron. One well-characterized terminal selector is COE (Collier/Olf/Ebf), which has been shown to activate cholinergic gene batteries in C. elegans motor neurons. However, its functions in other metazoans, particularly chordates, is less clear. Here we show that the sole COE ortholog in the non-vertebrate chordate Ciona robusta, Ebf, controls the expression of the cholinergic locus VAChT/ChAT in a single dorsal interneuron of the larval Motor Ganglion, which is presumed to be homologous to the vertebrate spinal cord. We propose that, while the function of Ebf as a regulator of cholinergic neuron identity conserved across bilaterians, its exact role may have diverged in different cholinergic neuron subtypes (e.g., interneurons vs. motor neurons) in chordate-specific motor circuits.

Rotavirus NSP1 Contributes to Intestinal Viral Replication, Pathogenesis, and Transmission

Rotavirus remains one of the most important causes of severe diarrhea and dehydration in young children worldwide. Although NSP1 is dispensable for rotavirus replication in cell culture, its exact role in virus infection in vivo remains unclear.

Shaping Presidential Powers in Hungary: Convention, Tradition and Informal Constitutional Amendments

There was no tradition of a republican president in Hungary before the fall of communism, and the transitory constitution of 1989 was unclear about the exact role the President should play in the constitutional system of Hungary. Some provisions even resembled those of presidential or semi-presidential systems; some ambiguities were clarified during the first two decades after the transition. Conventions, however, were established to some extent and sometimes very quickly. This period gave rise to guidelines as to how the powers of the President should be exercised. Some other powers were concretized and interpreted foremost by the Constitutional Court. These conventions and judicial interpretations formed the character of the Presidency to the extent of informal constitutional change. Some of these elements have even been incorporated into and formalized by the new Fundamental Law of Hungary. The present contribution will point out how the originally broad competencies of the President have been narrowed in the practice, and what role the Constitutional Court and political actors played in this process.

Contribution of Lactobacillus iners to Vaginal Health and Diseases: A Systematic Review

Lactobacillus iners, first described in 1999, is a prevalent bacterial species of the vaginal microbiome. As L. iners does not easily grow on de Man-Rogosa-Sharpe agar, but can grow anaerobically on blood agar, it has been initially overlooked by traditional culture methods. It was not until the wide application of molecular biology techniques that the function of L. iners in the vaginal microbiome was carefully explored. L. iners has the smallest genome among known Lactobacilli and it has many probiotic characteristics, but is partly different from other major vaginal Lactobacillus species, such as L. crispatus, in contributing to the maintenance of a healthy vaginal microbiome. It is not only commonly present in the healthy vagina but quite often recovered in high numbers in bacterial vaginosis (BV). Increasing evidence suggests that L. iners is a transitional species that colonizes after the vaginal environment is disturbed and offers overall less protection against vaginal dysbiosis and, subsequently, leads to BV, sexually transmitted infections, and adverse pregnancy outcomes. Accordingly, under certain conditions, L. iners is a genuine vaginal symbiont, but it also seems to be an opportunistic pathogen. Further studies are necessary to identify the exact role of this intriguing species in vaginal health and diseases.

Recognition and deubiquitination of free 40S for translational reset by Otu2

In actively translating 80S ribosomes the ribosomal protein eS7 of the 40S subunit is monoubiquitinated by the E3 ligase Not4 and deubiquitinated by the deubiquitination enzyme Otu2 upon ribosomal subunit recycling. Despite its importance for general efficiency of translation the exact role and structural basis for this specific translational reset are only poorly understood. Here we present biochemical and structural data showing that Otu2 can engage the recycled 40S subunit together with the recycling factors ABCE1 and Tma64 immediately after 60S dissociation for mRNA recycling, and that it dissociates before 48S initiation complex formation. A combined structural analysis of Otu2 and Otu2-40S complexes by X-ray crystallography, AlphaFold2 prediction and cryo-EM revealed how Otu2 can specifically be recruited to the 40S, but not to the 80S ribosome, for removal of the eS7-bound ubiquitin moiety. Here, interactions of the largely helical N-terminal domain of Otu2 to sites that are masked and therefore inaccessible in the 80S ribosome are of crucial importance. Collectively, we provide the structural basis for the Otu2 driven deubiquitination step providing a first mechanistic understanding of this translational reset step during ribosome recycling/(re)initiation.

Solving the Puzzle: What Is the Role of Progestogens in Neovascularization?

Ovarian sex steroids can modulate new vessel formation and development, and the clarification of the underlying mechanism will provide insight into neovascularization-related physiological changes and pathological conditions. Unlike estrogen, which mainly promotes neovascularization through activating classic post-receptor signaling pathways, progesterone (P4) regulates a variety of downstream factors with angiogenic or antiangiogenic effects, exerting various influences on neovascularization. Furthermore, diverse progestins, the synthetic progesterone receptor (PR) agonists structurally related to P4, have been used in numerous studies, which could contribute to unequal actions. As a result, there have been many conflicting observations in the past, making it difficult for researchers to define the exact role of progestogens (PR agonists including naturally occurring P4 and synthetic progestins). This review summarizes available evidence for progestogen-mediated neovascularization under physiological and pathological circumstances, and attempts to elaborate their functional characteristics and regulatory patterns from a comprehensive perspective.

Interleukin-31 promotes fibrosis and T helper 2 polarization in systemic sclerosis

Systemic sclerosis (SSc) is a chronic multisystem disorder characterized by fibrosis and autoimmunity. Interleukin (IL)-31 has been implicated in fibrosis and T helper (Th) 2 immune responses, both of which are characteristics of SSc. The exact role of IL-31 in SSc pathogenesis is unclear. Here we show the overexpression of IL-31 and IL-31 receptor A (IL-31RA) in dermal fibroblasts (DFs) from SSc patients. We elucidate the dual role of IL-31 in SSc, where IL-31 directly promotes collagen production in DFs and indirectly enhances Th2 immune responses by increasing pro-Th2 cytokine expression in DFs. Furthermore, blockade of IL-31 with anti-IL-31RA antibody significantly ameliorates fibrosis and Th2 polarization in a mouse model of SSc. Therefore, in addition to defining IL-31 as a mediator of fibrosis and Th2 immune responses in SSc, our study provides a rationale for targeting the IL-31/IL-31RA axis in the treatment of SSc.