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The cystic fibrosis transmembrane conductance regulator (CFTR) attenuates sphingosine-1-phosphate (S1P) signaling in resistance arteries and has emerged as a prominent regulator of myogenic vasoconstriction. This investigation demonstrates that S1P inhibits CFTR activity via adenosine monophosphate-activated kinase (AMPK), establishing a potential feedback link. In Baby Hamster Kidney (BHK) cells expressing wild-type human CFTR, S1P (1μmol/L) attenuates forskolin-stimulated, CFTR-dependent iodide efflux. S1P’s inhibitory effect is rapid (within 30 seconds), transient and correlates with CFTR serine residue 737 (S737) phosphorylation. Both S1P receptor antagonism (4μmol/L VPC 23019) and AMPK inhibition (80μmol/L Compound C or AMPK siRNA) attenuate S1P-stimluated (i) AMPK phosphorylation, (ii) CFTR S737 phosphorylation and (iii) CFTR activity inhibition. In BHK cells expressing the ΔF508 CFTR mutant (CFTRΔF508), the most common mutation causing cystic fibrosis, both S1P receptor antagonism and AMPK inhibition enhance CFTR activity, without instigating discernable correction. In summary, we demonstrate that S1P/AMPK signaling transiently attenuates CFTR activity. Since our previous work positions CFTR as a negative S1P signaling regulator, this signaling link may positively reinforce S1P signals. This discovery has clinical ramifications for the treatment of disease states associated with enhanced S1P signaling and/or deficient CFTR activity (e.g. cystic fibrosis, heart failure). S1P receptor/AMPK inhibition could synergistically enhance the efficacy of therapeutic strategies aiming to correct aberrant CFTR trafficking.

The limb-girdle muscular dystrophies (LGMD) are a collection of genetic diseases united in their phenotypical expression of pelvic and shoulder area weakness and wasting. More than 30 subtypes have been identified, five dominant and 26 recessive. The increase in the characterization of new genotypes in the family of LGMDs further adds to the heterogeneity of the disease. Meanwhile, better understanding of the phenotype led to the reconsideration of the disease definition, which resulted in eight old subtypes to be no longer recognized officially as LGMD and five new diseases to be added to the LGMD family. The unique variabilities of LGMD stem from genetic mutations, which then lead to protein and ultimately muscle dysfunction. Herein, we review the LGMD pathway, starting with the genetic mutations that encode proteins involved in muscle maintenance and repair, and including the genotype–phenotype relationship of the disease, the epidemiology, disease progression, burden of illness, and emerging treatments.

Membrane permeable bi‐arsenical dyes, such as fluorescein arsenical hairpin (FlAsH), bind tetracysteine‐tagged‐proteins emitting fluorescence in‐vivo. This fluorescence method (developed by R. Tsien) provides a tool to evaluate trafficking pathways in living cells. We generated a tetracysteine‐tagged Cystic Fibrosis Transmembrane Regulator (CFTR) protein and studied its expression with the long‐term goal of using this protein to study its trafficking during endocytosis. The tetracysteine‐tagged CFTR (CFTR‐TC) was predominantly expressed in both BHK and in Cos‐7 cells as the immature core‐glycosylated form (band B) rather than the mature glycosylated band C. Iodide efflux assays of CFTR‐TC's function as a chloride channel at the cell surface revealed an insignificant response after cAMP stimulation, likely reflecting its low band C expression. Interestingly, 1 hour FlAsH pre‐treatment evoked a mean response difference of −16.0 mV versus untreated (one‐way ANOVA p<0.05), suggesting increased band C expression. Our results suggest that FlAsH rescues the surface expression of CFTR‐TC and studies are ongoing to visualize its localization and the regulation of its trafficking by proteins involved in the endocytic pathway. The work is supported by the Natural Sciences and Engineering Research Council (postgraduate scholarship) and the Canadian Cystic Fibrosis Foundation BREATHE Program.