The α subunit of AMP-activated protein kinase is critical for the metabolic success and tachyzoite proliferation of Toxoplasma gondii.

Toxoplasma gondii is a zoonotic parasite infecting humans and nearly all warm-blooded animals. Successful parasitism in diverse hosts at various developmental stages requires the parasites to fine tune their metabolism according to environmental cues and the parasite's needs. By manipulating the ß and γ subunits, we have previously shown that AMP-activated protein kinase (AMPK) has critical roles in regulating the metabolic and developmental programmes. However, the biological functions of the α catalytic subunit have not been established. T. gondii encodes a canonical AMPKα, as well as a KIN kinase whose kinase domain has high sequence similarities to those of classic AMPKα proteins. Here, we found that TgKIN is dispensable for tachyzoite growth, whereas TgAMPKα is essential. Depletion of TgAMPKα expression resulted in decreased ATP levels and reduced metabolic flux in glycolysis and the tricarboxylic acid cycle, confirming that TgAMPK is involved in metabolic regulation and energy homeostasis in the parasite. Sequential truncations at the C-terminus found an α-helix that is key for the function of TgAMPKα. The amino acid sequences of this α-helix are not conserved among various AMPKα proteins, likely because it is involved in interactions with TgAMPKß, which only have limited sequence similarities to AMPKß in other eukaryotes. The essential role of the less conserved C-terminus of TgAMPKα provides opportunities for parasite specific drug designs targeting TgAMPKα.

The optimal cut-off values of screening tools for dynapenia: a cross-sectional study.

PURPOSE: This study evaluated whether anthropometric measurements and the five times sit-to-stand test could be used to identify dynapenia. The cut-off values of accurate screening tools for identifying dynapenia were also established. MATERIALS AND METHODS: This was a cross-sectional study conducted on individuals ≥ 60 years old (N = 529). All participants underwent handgrip strength measurement, anthropometric measurements and the five times sit-to-stand test. The participants whose handgrip strength was < 28 kg for men and < 18 kg for women were considered to have dynapenia. The association between the recorded variables and dynapenia was determined using logistic regression, and cut-off values were established by performing the Receiver Operating Characteristic curve analysis. RESULTS: The prevalence of dynapenia was 35.42% in men and 25.61% in women. For males, both calf circumference (≤ 35.2 cm) and the five times sit-to-stand test (≥ 14.6 s) could be used as accurate tools for dynapenia. For females, only the five times sit-to-stand test (≥ 11.8 s) had sufficient accuracy to be used as a screening tool for dynapenia. CONCLUSIONS: The five times sit-to-stand test was an accurate screening tool for identifying dynapenia. The calf circumference could be only used as a screening tool in males.

Calf circumference and the five times a sit-to-stand test can be used as accurate screening tools in males with dynapenia.Only the five times sit-to-stand test had sufficient accuracy in females with dynapenia.The optimal cut-off values established for older males and females are only applicable to the Asian population.

Two apicoplast dwelling glycolytic enzymes provide key substrates for metabolic pathways in the apicoplast and are critical for Toxoplasma growth.

Many apicomplexan parasites harbor a non-photosynthetic plastid called the apicoplast, which hosts important metabolic pathways like the methylerythritol 4-phosphate (MEP) pathway that synthesizes isoprenoid precursors. Yet many details in apicoplast metabolism are not well understood. In this study, we examined the physiological roles of four glycolytic enzymes in the apicoplast of Toxoplasma gondii. Many glycolytic enzymes in T. gondii have two or more isoforms. Endogenous tagging each of these enzymes found that four of them were localized to the apicoplast, including pyruvate kinase2 (PYK2), phosphoglycerate kinase 2 (PGK2), triosephosphate isomerase 2 (TPI2) and phosphoglyceraldehyde dehydrogenase 2 (GAPDH2). The ATP generating enzymes PYK2 and PGK2 were thought to be the main energy source of the apicoplast. Surprisingly, deleting PYK2 and PGK2 individually or simultaneously did not cause major defects on parasite growth or virulence. In contrast, TPI2 and GAPDH2 are critical for tachyzoite proliferation. Conditional depletion of TPI2 caused significant reduction in the levels of MEP pathway intermediates and led to parasite growth arrest. Reconstitution of another isoprenoid precursor synthesis pathway called the mevalonate pathway in the TPI2 depletion mutant partially rescued its growth defects. Similarly, knocking down the GAPDH2 enzyme that produces NADPH also reduced isoprenoid precursor synthesis through the MEP pathway and inhibited parasite proliferation. In addition, it reduced de novo fatty acid synthesis in the apicoplast. Together, these data suggest a model that the apicoplast dwelling TPI2 provides carbon source for the synthesis of isoprenoid precursor, whereas GAPDH2 supplies reducing power for pathways like MEP, fatty acid synthesis and ferredoxin redox system in T. gondii. As such, both enzymes are critical for parasite growth and serve as potential targets for anti-toxoplasmic intervention designs. On the other hand, the dispensability of PYK2 and PGK2 suggest additional sources for energy in the apicoplast, which deserves further investigation.

Effects of flexi-bar training on muscle strength and physical performance in older people with dynapenia: the protocol of a randomised controlled trial.

INTRODUCTION: Dynapenia is a new term that is used to describe the age-related loss of muscle strength. Flexi-bar training is a safe and feasible device for older people with dynapenia. This study will investigate the effects of a 12-week flexi-bar training programme on muscle strength and physical function in older people with dynapenia. METHODS AND ANALYSIS: A total of 114 participants (aged more than 65 years) with age-related muscle loss will participate in a 12-week flexi-bar training programme. The participants will be randomly divided into three groups, namely, flexi-bar, placebo and control, with equal number of participants in each group. The assessments will be conducted at preintervention, postintervention and 12 weeks after training completion. The primary outcome is timed-up-and-go test. The secondary outcomes are five-repetition sit-to-stand test, 10-metre walking test, handgrip strength, as well as the serum albumin and haemoglobin levels. ETHICS AND DISSEMINATION: The procedures of this study were reviewed and approved by the Human Ethics Review Board of Wuhan Brain Hospital (General Hospital of the Yangtze River Shipping) on 29 September 2020 (#L20200013). The findings of this study will be published in peer-reviewed journals and presented at conferences. The trial was registered on 6 November 2020. TRIAL REGISTRATION NUMBER: ISRCTN14316668.