Lack of age-related respiratory changes in Daphnia

Abstract

Aging is a multifaceted process of accumulation of damages and waste in cells and tissues; age-related changes in mitochondria and in respiratory metabolism have been in the focus of aging research for decades. Here we investigated age-related changes in respiration rates, lactate/pyruvate ratio, a commonly used proxy for NAD+/NADH balance, and mitochondrial membrane potential in 4 genotypes of an emerging model organism for aging research, a cyclic parthenogen Daphnia magna. We show that total body weight-adjusted respiration rate decreases with age, although this decrease is small in magnitude and not observed in anaesthetized animals, thus likely to be accounted for by decrease in locomotion and feeding activity. Lactate/pyruvate ratio and mitochondrial membrane potential (Ψ mt ) showed no age-related changes, with a possible exception of Ψ mt measured in the optical lobe and in epipodites (excretory organs) in which Ψ mt showed a maximum at middle age. We conclude that actuarial senescence in Daphnia is not caused by a decline in respiratory metabolism and discuss possible mechanisms of maintaining mitochondrial healthspan throughout the lifespan.

The interplay between prior selection, mild intermittent exposure, and acute severe exposure in phenotypic and transcriptional response to hypoxia

“…Respiration rate was measured in individual Daphnia sampled from the cohorts, 12 replicates per clone per treatment for the FI and HU clones and 18 replicates per clone per treatment for the IL and GB clones, due to availability. As described in Anderson et al (2022), Daphnia were individually placed in either 200 μl or 1700 μl 24‐well respirometry glass plates (Loligo®), after which the plates were sealed with PCR sealing tape, and oxygen concentration measured using SDR fluorescence sensors (PreSens). Either normoxic (8 mg O 2 /L) or hypoxic (4 mg O 2 /L) COMBO water was used in these measurements.…”

“…Sixteen individuals were sampled per clone per CMIH treatment; in two cases some replicates were lost, resulting in 12 and 8 replicates. ΔΨ m was measured by means of rhodamine‐123 assays as described in Anderson et al (2022). Briefly, Daphnia were exposed for 24 h to a 4 μM solution of rhodamine‐123 dye, washed three times, and photographed using a Leica DM3000 microscope with a 10× objective (0.22 aperture) equipped with a Leica DFc450C color camera, with a 488 nm excitation/broadband (>515 nm) emission filter.…”

“…It is reasonable to assume that Daphnia originating from these habitats have been under a stronger selection favoring hypoxia adaptation than those originating from more permanent water bodies. Previous studies (Anderson et al, 2022; Coggins et al, 2021) indicated that the two clones from the intermittent habitats had lower lifespan and higher propensity for sexual reproduction than the two clones from more permanent water bodies, so we anticipated differences in lifespan effects of hypoxia.…”

Prior selection affects phenotypic and transcriptional response to hypoxia

“…Samples for mitochondrial membrane potential (ΔΨ m ) measurements were taken from the cohorts at the median lifespan of all cohorts, i.e., at the age of 80 days to maximize longevity-related effects. ΔΨ m was measured by means of rhodamine-123 assays as described in Anderson et al (2022). Briefly, Daphnia were exposed for 24 h to a M solution of rhodamine-123 dye, washed 3 times, and photographed using a Leica μ DM3000 microscope with a 10x objective (0.22 aperture) equipped with a Leica DFc450C color camera, with a 488 nm excitation / broadband (>515 nm) emission filter.…”

Dietary polyunsaturated fatty acids affect longevity, heat tolerance, lipid peroxidation and mitochondrial membrane potential in Daphnia.

“…Daphnia clones used in this study were obtained from Basel University stock collection (Basel, Switzerland) and have been maintained in the lab for over 5 years in COMBO water (Kilham et al 1998) at 20 o C under 12:12 L:D photoperiod, fed a Scenedesmus algae diet. For data on clones' geographic origins and prior data on lifespan see Anderson et al (2022). Throughout this paper the clones will be referred to by their two-letter codes indicating country of origin, namely Finland (FI), Great Britain (GB), Hungary (HU), and Israel (IL).…”