mTOR inhibition and BMP signaling act synergistically to reduce muscle fibrosis and improve myofiber regeneration.

Muscle trauma is highly morbid due to intramuscular scarring, or fibrosis, and muscle atrophy. Studies have shown that bone morphogenetic proteins (BMPs) reduce muscle atrophy. However, increased BMP signaling at muscle injury sites causes heterotopic ossification, as seen in patients with fibrodysplasia ossificans progressiva (FOP), or patients with surgically placed BMP implants for bone healing. We use a genetic mouse model of hyperactive BMP signaling to show the development of intramuscular fibrosis surrounding areas of ectopic bone following muscle injury. Rapamycin, which we have previously shown to eliminate ectopic ossification in this model, also eliminates fibrosis without reducing osteogenic differentiation, suggesting clinical value for patients with FOP and with BMP implants. Finally, we use reporter mice to show that BMP signaling is positively associated with myofiber cross-sectional area. These findings underscore an approach in which 2 therapeutics (rapamycin and BMP ligand) can offset each other, leading to an improved outcome.

Diminished Chondrogenesis and Enhanced Osteoclastogenesis in Leptin-Deficient Diabetic Mice (ob/ob) Impair Pathologic, Trauma-Induced Heterotopic Ossification.

Diabetic trauma patients exhibit delayed postsurgical wound, bony healing, and dysregulated bone development. However, the impact of diabetes on the pathologic development of ectopic bone or heterotopic ossification (HO) following trauma is unknown. In this study, we use leptin-deficient mice as a model for type 2 diabetes to understand how post-traumatic HO development may be affected by this disease process. Male leptin-deficient (ob/ob) or wild-type (C57BL/6 background) mice aged 6-8 weeks underwent 30% total body surface area burn injury with left hind limb Achilles tenotomy. Micro-CT (µCT) imaging showed significantly lower HO volumes in diabetic mice compared with wild-type controls (0.70 vs. 7.02 mm(3), P < 0.01) 9 weeks after trauma. Ob/ob mice showed evidence of HO resorption between weeks 5 and 9. Quantitative real time PCR (qRT-PCR) demonstrated high Vegfa levels in ob/ob mice, which was followed by disorganized vessel growth at 7 weeks. We noted diminished chondrogenic gene expression (SOX9) and diminished cartilage formation at 5 days and 3 weeks, respectively. Tartrate-resistant acid phosphatase stain showed increased osteoclast presence in normal native bone and pathologic ectopic bone in ob/ob mice. Our findings suggest that early diminished HO in ob/ob mice is related to diminished chondrogenic differentiation, while later bone resorption is related to osteoclast presence.

Aberrant localization of fusion receptors involved in regulated exocytosis in salivary glands of Sjögren's syndrome patients is linked to ectopic mucin secretion.

Sjögren's syndrome (SS) is a chronic inflammatory autoimmune disease that mainly affects tear and salivary glands, whereby SS-patients frequently complain of eye and mouth dryness. Salivary acinar cells of SS-patients display alterations in their cell polarity; which may affect the correct localization and function of proteins involved in regulated exocytosis. Here we determined whether the expression and localization of SNARE proteins (membrane fusion receptors) involved in regulated secretion, such as VAMP8, syntaxin 3 (STX3), STX4 and SNAP-23 were altered in salivary glands (SG) from SS-patients. Additionally, we investigated SNARE proteins function, by evaluating their ability to form SNARE complexes under basal conditions. In SG from SS-patients and control subjects mRNA and proteins levels of SNARE complex components were determined by real-time PCR and Western blotting, respectively. SNARE protein distribution and mucin exocytosis were determined by indirect immunofluorescence. In SS-patients, the expression levels of mRNA and protein for VAMP8, STX4 and STX3 were altered. STX4, STX3, SNAP-23 and VAMP8 relocated from the apical to the basal region of acinar cells. Increased formation of SNARE complexes in a manner independent of external stimuli for secretion was detected. Mucins were detected in the extracellular matrix (ECM). Presence of mucins in the ECM, together with the observed alterations in SNARE protein localization is indicative of ectopic exocytosis. In the context of SS, such aberrantly localized mucins are likely to favor a pro-inflammatory response, which may represent an important initial step in the pathogenesis of this disease.