Direct anabolic metabolism of three-carbon propionate to a six-carbon metabolite occurs in vivo across tissues and species

Anabolic metabolism of carbon in mammals is mediated via the one- and two-carbon carriers S-adenosyl methionine and acetyl-coenzyme A. In contrast, anabolic metabolism of three-carbon units via propionate has not been shown to extensively occur. Mammals are primarily thought to oxidize the three-carbon short chain fatty acid propionate by shunting propionyl-CoA to succinyl-CoA for entry into the TCA cycle. Here, we found that this may not be absolute as, in mammals, one nonoxidative fate of propionyl-CoA is to condense to two three-carbon units into a six-carbon trans-2-methyl-2-pentenoyl-CoA (2M2PE-CoA). We confirmed this reaction pathway using purified protein extracts provided limited substrates and verified the product via LC-MS using a synthetic standard. In whole-body in vivo stable isotope tracing following infusion of ¹³C-labeled valine at steady state, 2M2PE-CoA was found to form via propionyl-CoA in multiple murine tissues, including heart, kidney, and to a lesser degree, in brown adipose tissue, liver, and tibialis anterior muscle. Using ex vivo isotope tracing, we found that 2M2PE-CoA also formed in human myocardial tissue incubated with propionate to a limited extent. While the complete enzymology of this pathway remains to be elucidated, these results confirm the in vivo existence of at least one anabolic three- to six-carbon reaction conserved in humans and mice that utilizes propionate.     

Oxygen stable isotope ratios of tree-ring cellulose: the next phase of understanding

Analysis of the oxygen isotope ratio of tree-ring cellulose is a valuable tool that can be used as a paleoclimate proxy. Our ability to use this tool has gone through different phases. The first began in the 1970s with the demonstration of empirical relationships between the oxygen isotope ratio of tree-ring cellulose and climate. These empirical relationships, however, did not provide us with the confidence that they are robust through time, across taxa and across geographical locations. The second phase began with a rudimentary understanding of the physiological and biochemical mechanisms responsible for the oxygen isotope ratios of cellulose, which is necessary to increase the power of this tool. This phase culminated in a mechanistic tree-ring model integrating concepts of physiology and biochemistry in a whole-plant system. This model made several assumptions about leaf water isotopic enrichment and biochemistry which, in the nascent third phase, are now being challenged, with surprising results. These third-phase results suggest that, contrary to the model assumption, leaf temperature across a large latitudinal gradient is remarkably constant and does not follow ambient temperature. Recent findings also indicate that the biochemistry responsible for the incorporation of the cellulose oxygen isotopic signature is not as simple as has been assumed. Interestingly, the results of these challenges have strengthened the tree-ring model. There are several other assumptions that can be investigated which will improve the utility of the tree-ring model.     

Tissue-Characteristic Expression of Mouse Proteome

The mouse is a valuable model organism for biomedical research. Here, we established a comprehensive spectral library and the data-independent acquisition–based quantitative proteome maps for 41 mouse organs, including some rarely reported organs such as the cornea, retina, and nine paired organs. The mouse spectral library contained 178,304 peptides from 12,320 proteins, including 1678 proteins not reported in previous mouse spectral libraries. Our data suggested that organs from the nervous system and immune system expressed the most distinct proteome compared with other organs. We also found characteristic protein expression of immune-privileged organs, which may help understanding possible immune rejection after organ transplantation. Each tissue type expressed characteristic high-abundance proteins related to its physiological functions. We also uncovered some tissue-specific proteins which have not been reported previously. The testis expressed highest number of tissue-specific proteins. By comparison of nine paired organs including kidneys, testes, and adrenal glands, we found left organs exhibited higher levels of antioxidant enzymes. We also observed expression asymmetry for proteins related to the apoptotic process, tumor suppression, and organ functions between the left and right sides. This study provides a comprehensive spectral library and a quantitative proteome resource for mouse studies.     

Stomoxys calcitrans,mechanical vector of virulent Besnoitia besnoiti from chronically infected cattle to susceptible rabbit

Cattle besnoitiosis caused by Besnoitia besnoiti (Eucoccidiorida: Sarcocystidae) is a re‐emerging disease in Europe. Its mechanical transmission by biting flies has not been investigated since the 1960s. The aim of this study was to re‐examine the ability of Stomoxys calcitrans (Diptera: Muscidae) to transmit virulent B. besnoiti bradyzoites from chronically infected cows to susceptible rabbits. Three batches of 300 stable flies were allowed to take an interrupted bloodmeal on chronically infected cows, followed by an immediate bloodmeal on three rabbits (Group B). A control group of rabbits and a group exposed to the bites of non‐infected S. calcitrans were included in the study. Blood quantitative polymerase chain reaction (qPCR) analyses, and clinical, serological and haematological surveys were performed in the three groups over 152 days until the rabbits were killed. Quantitative PCR analyses and histological examinations were performed in 24 tissue samples per rabbit. Only one rabbit in Group B exhibited clinical signs of the acute phase of besnoitiosis (hyperthermia, weight loss, regenerative anaemia and transient positive qPCR in blood) and was seroconverted. Parasite DNA was detected in four tissue samples from this rabbit, but no cysts were observed on histological examination. These findings indicate that S. calcitrans may act as a mechanical vector of B. besnoiti more efficiently than was previously considered.     

Host identification in unfed ticks from stable isotope compositions (δ13C and δ15N)

Determination of the ratios of natural stable isotopes (¹³C/¹²C and ¹⁵N/¹⁴N) in unfed Ixodes ricinus nymphs and adults, which, in their previous stage, fed on captive wild rodents (Apodemus sylvaticus and Myodes glareolus), wild birds (Parus major and Cyanistes caeruleus) or domestic ruminants (Ovis aries and Bos taurus), demonstrated that it is possible to identify each host category with confidence. First, the tick–blood spacing, which is the difference between values obtained from ticks and the blood of hosts that they had fed on in the previous stage, was consistent (152 spacings investigated from 15 host individuals in total). Second, potential confounding factors (tick age and sex) did not affect the discriminatory power of the isotope patterns, nor did different rearing conditions (room temperature vs. 4 °C) or the duration of development (maximum of 430 days). The findings that the tick–blood isotope spacings, across a diverse range of hosts, were similar and predictable, and that confounders had little or no effect on this, strongly support the usage of the isotope approach. Because each of the host categories has a different role in the population dynamics of I. ricinus and in tick‐borne pathogen ecology, the method described here has great potential for the clarification of tick and tick‐borne pathogen ecology in the field.