Glucose signaling is important for nutrient adaptation during differentiation of pleomorphic African trypanosomes

Abstract

18The African trypanosome has evolved mechanisms to adapt to changes in 19 nutrient availability that occur during its lifecycle. During transition from mammalian 20 blood to insect vector gut, parasites experience a rapid reduction in environmental 21 glucose. Here we describe how pleomorphic parasites respond to glucose depletion 22 with a focus on parasite changes in energy metabolism and growth. Long slender 23 bloodstream form parasites are rapidly killed as glucose concentrations fall, while the 24 short stumpy bloodstream form parasites persist to differentiate into the insect stage 25 procyclic form parasite. The rate of differentiation was slower than that triggered by 26 other cues but reached physiological rates when combined with cold shock. Both 27 differentiation and growth of resulting procyclic form parasites were inhibited by glucose 28 and its non-metabolizable analogs in a concentration dependent manner. Procyclic 29 form parasites differentiated from short stumpy form parasites in glucose depleted 30 medium significantly upregulated gene expression of amino acid metabolic pathway 31 components when compared to procyclic forms generated by cis-aconitate treatment. 32Additionally, growth of these parasite was inhibited by the presence of either glucose or 33 6-deoxyglucose. In summary, glucose transitions from the primary metabolite of the 34 blood stage infection to a negative regulator of cell development and growth in the 35 insect vector, suggesting that the hexose is not only a key metabolic agent but is also 36 an important signaling molecule. 37 38 39 Author Summary 40. CC-BY-ND 4.0 International license It is made available under a (which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint . http://dx.doi.org/10.1101/346601 doi: bioRxiv preprint first posted online Jun. 13, 2018; 3 As the African trypanosome, Trypanosoma brucei, completes its lifecycle, it 41 encounters many different environments. Adaptation to these environments includes 42 modulation of metabolic pathways to parallel the availability of nutrients. Here, we 43 describe how the blood-dwelling lifecycle stages of the African trypanosome, which 44 consume glucose to meet their nutritional needs, respond differently to culture in the 45 near absence of glucose. The proliferative long slender parasites rapidly die, while the 46 non-dividing short stumpy remains viable and undergoes differentiation to the next 47 lifecycle stage, the procyclic form parasite. Interestingly a sugar analog that cannot be 48 used as an energy source inhibited the process. Furthermore, the growth of procyclic 49 form parasite that resulted from the event was inhibited by glucose, a behavior that is 50 similar to that of parasites isolated from tsetse flies. Our findings suggest that glucose 51 sensing serves as an important modulator of nutrient adaptation in the parasite. 52 53

Nutrient availability regulates proline/alanine transporters in Trypanosoma brucei

“…This suggests that AAT7-B expression is connected to a switch in energy metabolism. While AAT7-B genes are expressed in all developmental stages, transcript levels of the individual genes were found to differ between BSF and PCF in several studies; these consistently showed a prevalence of Tb927.8.7610 in BSF and Tb927.8.7640 in the procyclic form ( 17 , 39 , 41 , 42 , 43 , 44 , 45 , 46 , 68 ). This is comparable to our results with approx.…”

“…It was found that short stumpy BSF preadapts to life in their future insect host ( 69 ), for example, by increasing expression of enzymes of the TCA cycle, change of their excreted end products from pyruvate toward acetate and succinate ( 39 , 69 , 70 , 71 ), and by elevating transcripts of proline-metabolizing enzymes ( 17 , 39 , 41 ). Though higher AAT7-B transcript or protein levels were occasionally identified in short stumpy BSF ( 17 , 72 ), in the majority of studies no major regulation was reported ( 41 , 45 , 46 , 68 ) indicating that AAT7-B expression may be altered only once stumpy forms enter the insect host i.e. , during the transition to procyclic forms and induced by nutrient or energy availability.…”

“…Proline is used by T. brucei to fuel oxidative phosphorylation in the mitochondrion and is the main source of energy for the insect stages of the parasite ( 13 ). Proline metabolism has been studied extensively ( 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ) and is of fundamental importance for the survival of T. brucei in the tsetse fly ( 13 ). The first two enzymes of proline degradation, proline dehydrogenase and Δ 1 -pyrroline-5-carboxylate dehydrogenase (P5CDH), are essential for the parasite's grown in the absence of glucose in vitro ( 13 , 14 ), and parasites lacking P5CDH fail to establish tsetse fly midgut infections in vivo ( 13 ).…”

“…Because proline degradation is linked to the TCA cycle, it is interesting that TCA cycle intermediates can initiate the differentiation from short stumpy bloodstream forms to procyclic forms ( 25 ). This differentiation can also be triggered by depriving stumpy forms of glucose, which concomitantly induces upregulation of enzymes involved in proline degradation ( 17 ). Similarly, upregulation of proline metabolism as well as an increase in proline uptake and consumption was shown in procyclic culture forms (PCF) shifted from glucose-containing to glucose-free medium ( 14 ).…”

The zinc finger proteins ZC3H20 and ZC3H21 stabilise mRNAs encoding membrane proteins and mitochondrial proteins in insect‐form Trypanosoma brucei

“…One possibility is a response to stress, although there was no correlation with the effects of heat shock (Minia, Merce, Terrao, & Clayton, ) or starvation (Fritz et al, ). Altered metabolite levels could also be responsible (Bringaud et al, ; Fernandez‐Moya, Carrington, & Estevez, ; Qiu et al, ; Vassella et al, , ); and it is conceivable that one or more of the directly regulated surface proteins acts as a receptor for a signal that maintains procyclic identity.…”