Translocation and dissemination to target neurons of botulinum neurotoxin type B in the mouse intestinal wall

Botulinum neurotoxins (BoNTs) are responsible for severe flaccid paralysis (botulism), which in most cases enter the organism via the digestive tract and then disseminate into the blood or lymph circulation to target autonomic and motor nerve endings. The passage way of BoNTs alone or in complex forms with associated nontoxic proteins through the epithelial barrier of the digestive tract still remains unclear. Here, we show using an in vivo model of mouse ligated intestinal loop that BoNT/B alone or the BoNT/B C‐terminal domain of the heavy chain (HCcB), which interacts with cell surface receptors, translocates across the intestinal barrier. The BoNT/B or HCcB translocation through the intestinal barrier occurred via an endocytosis‐dependent mechanism within 10–20 min, because Dynasore, a potent endocytosis inhibitor, significantly prevented BoNT/B as well as HCcB translocation. We also show that HCcB or BoNT/B specifically targets neuronal cells and neuronal extensions in the intestinal submucosa and musculosa expressing synaptotagmin, preferentially cholinergic neurons and to a lower extent other neuronal cell types, notably serotonergic neurons. Interestingly, rare intestinal epithelial cells accumulated HCcB suggesting that distinct cell types of the intestinal epithelium, still undefined, might mediate efficient translocation of BoNT/B.     

Aging Contributes to Inflammation in Upper Extremity Tendons and Declines in Forelimb Agility in a Rat Model of Upper Extremity Overuse

We sought to determine if tendon inflammatory and histopathological responses increase in aged rats compared to young rats performing a voluntary upper extremity repetitive task, and if these changes are associated with motor declines. Ninety-six female Sprague-Dawley rats were used in the rat model of upper extremity overuse: 67 aged and 29 young adult rats. After a training period of 4 weeks, task rats performed a voluntary high repetition low force (HRLF) handle-pulling task for 2 hrs/day, 3 days/wk for up to 12 weeks. Upper extremity motor function was assessed, as were inflammatory and histomorphological changes in flexor digitorum and supraspinatus tendons. The percentage of successful reaches improved in young adult HRLF rats, but not in aged HRLF rats. Forelimb agility decreased transiently in young adult HRLF rats, but persistently in aged HRLF rats. HRLF task performance for 12 weeks lead to increased IL-1beta and IL-6 in flexor digitorum tendons of aged HRLF rats, compared to aged normal control (NC) as well as young adult HRLF rats. In contrast, TNF-alpha increased more in flexor digitorum tendons of young adult 12-week HRLF rats than in aged HRLF rats. Vascularity and collagen fibril organization were not affected by task performance in flexor digitorum tendons of either age group, although cellularity increased in both. By week 12 of HRLF task performance, vascularity and cellularity increased in the supraspinatus tendons of only aged rats. The increased cellularity was due to increased macrophages and connective tissue growth factor (CTGF)-immunoreactive fibroblasts in the peritendon. In conclusion, aged rat tendons were overall more affected by the HRLF task than young adult tendons, particularly supraspinatus tendons. Greater inflammatory changes in aged HRLF rat tendons were observed, increases associated temporally with decreased forelimb agility and lack of improvement in task success.     

Structure of a C. perfringens Enterotoxin Mutant in Complex with a Modified Claudin-2 Extracellular Loop 2

CPE (Clostridium perfringens enterotoxin) is the major virulence determinant for C. perfringens type-A food poisoning, the second most common bacterial food-borne illness in the UK and USA. After binding to its receptors, which include particular human claudins, the toxin forms pores in the cell membrane. The mature pore apparently contains a hexamer of CPE, claudin and, possibly, occludin. The combination of high binding specificity with cytotoxicity has resulted in CPE being investigated, with some success, as a targeted cytotoxic agent for oncotherapy. In this paper, we present the X-ray crystallographic structure of CPE in complex with a peptide derived from extracellular loop 2 of a modified, CPE-binding Claudin-2, together with high-resolution native and pore-formation mutant structures. Our structure provides the first atomic-resolution data on any part of a claudin molecule and reveals that claudin's CPE-binding fingerprint (NPLVP) is in a tight turn conformation and binds, as expected, in CPE's C-terminal claudin-binding groove. The leucine and valine residues insert into the binding groove while the first residue, asparagine, tethers the peptide via an interaction with CPE's aspartate 225 and the two prolines are required to maintain the tight turn conformation. Understanding the structural basis of the contribution these residues make to binding will aid in engineering CPE to target tumor cells.     

Organization and regulation of the neurotoxin genes in Clostridium botulinum and Clostridium tetani

Botulinum and tetanus neurotoxins are structurally and functionally related 150 kDa proteins that are potent inhibitors of neuroexocytosis. Botulinum neurotoxin associates with non-toxic proteins to form complexes of various sizes. The botulinum neurotoxin and non-toxic protein genes are clustered in a DNA segment called the botulinum locus. This locus is probably located on a mobile or degenerate mobile element, which accounts for the various genomic localizations (chromosome, plasmid, phage) in different Clostridium botulinum types. The botulinum neurotoxin and non-toxic protein genes are organized in two polycistronic operons (ntnh-bont and ha operons) transcribed in opposite orientations. The gene that separates the two operons of the botulinum locus in C. botulinum A encodes a 21 kDa protein BotR/A, which is a positive regulator of the expression of the botulinum locus genes. Similarly, in Clostridium tetani, the gene located immediately upstream of the tetanus toxin gene, encodes a positive regulatory protein, TetR. BotR and TetR are possibly alternative sigma factors related to TxeR and UviA, which regulate C. difficile toxin and C. perfringens bacteriocin production, respectively. TxeR and UviA define a new sub-group of the sigma(70) family of RNA polymerase initiation factors. In addition, the C. botulinum genome contains predicted two-component system genes, some of which are possibly involved in regulation of toxinogenesis.     

Activation of a c-Jun-NH2-terminal kinase pathway by the lethal toxin from Clostridium sordellii, TcsL-82, occurs independently of the toxin intrinsic enzymatic activity and facilitates small GTPase glucosylation

In the present study, we show that lethal toxin from Clostridium sordellii (TcsL-82) activates the three MAP kinase pathways, but that only a permeable and specific c-Jun-NH2-terminal kinase (JNK) inhibitor, JNK inhibitor II, prevents toxin-dependent actin depolymerization and cell rounding. We show that JNK activation is dependent on entry of the toxin N-terminal domain into the cytosol as bafilomycin A1, which prevents acidification of endocytic vesicle and subsequent cytosolic translocation of the toxin N-terminal domain, prevents JNK activation. Inhibition of JNK activity delays small GTPase glucosylation generated by N-terminal domain catalytic activity. Using a cell line mutant deficient in UDP-glucose, we observed that activation of JNK occurs even in the absence of small GTPase glucosylation and, thus, is independent of the toxin intrinsic catalytic activity. Facilitation of target glucosylation by JNK activation appeared to be restricted to TcsL-82 and was not a general feature of large clostridial toxins. Indeed, it was not observed with Toxin B from Clostridium difficile although this toxin also activates JNK.