Mitra Lavasani

Environmental Factors in Parkinson’s Disease

Evidence discussed in this review article lends strong support in favor of an etiologic role of environmentalfactors in Parkinsons disease. First, thanks to the discovery of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), it is now clear that, by targeting the nigrostriatal system, neurotoxicants can reproduce the neurochemical and pathological features of idiopathic parkinsonism. The sequence of toxic events triggered by MPTP has also provided us with intriguing clues concerning mechanisms of toxicant selectivity and nigrostriatal vulnerability. Relevant examples are (i) the role of the plasma membrane dopamine transporter in facilitating the access of potentially toxic species into dopaminergic neurons; (ii) the vulnerability of the nigrostriatal system to failure of mitochondrial energy metabolism; and (iii) the contribution of inflammatory processes to tissue lesioning. Epidemiological and experimental data suggest the potential involvement of specific agents as neurotoxicants (e.g. pesticides) or neuroprotective compounds (e.g. tobacco products) in the pathogenesis of nigrostriatal degeneration, further supporting a relationship between the environment and Parkinsons disease. A likely scenario that emerges from our current knowledge is that neurodegeneration results from multiple events and interactive mechanisms. These may include (i) the synergistic action of endogenous and exogenous toxins (e.g. the ability of the pesticide diethyldithiocarbamate to promote the toxicity of other compounds); (ii) the interactions of toxic agents with endogenous elements (e.g. the protein alpha-synuclein); (iii) the tissue response to an initial toxic insult; and, last but not least, (iv) the effects of environmental factors on the background of genetic predisposition and aging.

Relationships between Transforming Growth Factor-β1, Myostatin, and Decorin IMPLICATIONS FOR SKELETAL MUSCLE FIBROSIS

Recent studies have shown that myostatin, first identified as a negative regulator of skeletal muscle growth, may also be involved in the formation of fibrosis within skeletal muscle. In this study, we further explored the potential role of myostatin in skeletal muscle fibrosis, as well as its interaction with both transforming growth factor-β1 and decorin. We discovered that myostatin stimulated fibroblast proliferation in vitro and induced its differentiation into myofibroblasts. We further found that transforming growth factor-β1 stimulated myostatin expression, and conversely, myostatin stimulated transforming growth factor-β1 secretion in C2C12 myoblasts. Decorin, a small leucine-rich proteoglycan, was found to neutralize the effects of myostatin in both fibroblasts and myoblasts. Moreover, decorin up-regulated the expression of follistatin, an antagonist of myostatin. The results of in vivo experiments showed that myostatin knock-out mice developed significantly less fibrosis and displayed better skeletal muscle regeneration when compared with wild-type mice at 2 and 4 weeks following gastrocnemius muscle laceration injury. In wild-type mice, we found that transforming growth factor-β1 and myostatin co-localize in myofibers in the early stages of injury. Recombinant myostatin protein stimulated myofibers to express transforming growth factor-β1 in skeletal muscles at early time points following injection. In summary, these findings define a fibrogenic property of myostatin and suggest the existence of co-regulatory relationships between transforming growth factor-β1, myostatin, and decorin.

Muscle-derived stem/progenitor cell dysfunction limits healthspan and lifespan in a murine progeria model

With ageing, there is a loss of adult stem cell function. However, there is no direct evidence that this has a causal role in ageing-related decline. We tested this using muscle-derived stem/progenitor cells (MDSPCs) in a murine progeria model. Here we show that MDSPCs from old and progeroid mice are defective in proliferation and multilineage differentiation. Intraperitoneal administration of MDSPCs, isolated from young wild-type mice, to progeroid mice confer significant lifespan and healthspan extension. The transplanted MDSPCs improve degenerative changes and vascularization in tissues where donor cells are not detected, suggesting that their therapeutic effect may be mediated by secreted factor(s). Indeed, young wild-type-MDSPCs rescue proliferation and differentiation defects of aged MDSPCs when co-cultured. These results establish that adult stem/progenitor cell dysfunction contributes to ageing-related degeneration and suggests a therapeutic potential of post-natal stem cells to extend health.

NF-κB Negatively Impacts the Myogenic Potential of Muscle-derived Stem Cells

Inhibition of the inhibitor of kappa B kinase (IKK)/nuclear factor-kappa B (NF-κB) pathway enhances muscle regeneration in injured and diseased skeletal muscle, but it is unclear exactly how this pathway contributes to the regeneration process. In this study, we examined the role of NF-κB in regulating the proliferation and differentiation of muscle-derived stem cells (MDSCs). MDSCs isolated from the skeletal muscles of p65(+/-) mice (haploinsufficient for the p65 subunit of NF-κB) had enhanced proliferation and myogenic differentiation compared to MDSCs isolated from wild-type (wt) littermates. In addition, selective pharmacological inhibition of IKKβ, an upstream activator of NF-κB, enhanced wt MDSC differentiation into myotubes in vitro. The p65(+/-) MDSCs also displayed a higher muscle regeneration index than wt MDSCs following implantation into adult mice with muscular dystrophy. Additionally, using a muscle injury model, we observed that p65(+/-) MDSC engraftments were associated with reduced inflammation and necrosis. These results suggest that inhibition of the IKK/NF-κB pathway represents an effective approach to improve the myogenic regenerative potential of MDSCs and possibly other adult stem cell populations. Moreover, our results suggest that the improved muscle regeneration observed following inhibition of IKK/NF-κB, is mediated, at least in part, through enhanced stem cell proliferation and myogenic potential.

Human muscle-derived stem/progenitor cells promote functional murine peripheral nerve regeneration

Peripheral nerve injuries and neuropathies lead to profound functional deficits. Here, we have demonstrated that muscle-derived stem/progenitor cells (MDSPCs) isolated from adult human skeletal muscle (hMDSPCs) can adopt neuronal and glial phenotypes in vitro and ameliorate a critical-sized sciatic nerve injury and its associated defects in a murine model. Transplanted hMDSPCs surrounded the axonal growth cone, while hMDSPCs infiltrating the regenerating nerve differentiated into myelinating Schwann cells. Engraftment of hMDSPCs into the area of the damaged nerve promoted axonal regeneration, which led to functional recovery as measured by sustained gait improvement. Furthermore, no adverse effects were observed in these animals up to 18 months after transplantation. Following hMDSPC therapy, gastrocnemius muscles from mice exhibited substantially less muscle atrophy, an increase in muscle mass after denervation, and reorganization of motor endplates at the postsynaptic sites compared with those from PBS-treated mice. Evaluation of nerve defects in animals transplanted with vehicle-only or myoblast-like cells did not reveal histological or functional recovery. These data demonstrate the efficacy of hMDSPC-based therapy for peripheral nerve injury and suggest that hMDSPC transplantation has potential to be translated for use in human neuropathies.

Platelet-Rich Plasma Promotes the Proliferation of Human Muscle Derived Progenitor Cells and Maintains Their Stemness

Human muscle-derived progenitor cells (hMDPCs) offer great promise for muscle cell-based regenerative medicine; however, prolonged ex-vivo expansion using animal sera is necessary to acquire sufficient cells for transplantation. Due to the risks associated with the use of animal sera, the development of a strategy for the ex vivo expansion of hMDPCs is required. The purpose of this study was to investigate the efficacy of using platelet-rich plasma (PRP) for the ex-vivo expansion of hMDPCs. Pre-plated MDPCs, myoendothelial cells, and pericytes are three populations of hMDPCs that we isolated by the modified pre-plate technique and Fluorescence Activated Cell Sorting (FACS), respectively. Pooled allogeneic human PRP was obtained from a local blood bank, and the effect that thrombin-activated PRP-releasate supplemented media had on the ex-vivo expansion of the hMDPCs was tested against FBS supplemented media, both in vitro and in vivo. PRP significantly enhanced short and long-term cell proliferation, with or without FBS supplementation. Antibody-neutralization of PDGF significantly blocked the mitogenic/proliferative effects that PRP had on the hMDPCs. A more stable and sustained expression of markers associated with stemness, and a decreased expression of lineage specific markers was observed in the PRP-expanded cells when compared with the FBS-expanded cells. The in vitro osteogenic, chondrogenic, and myogenic differentiation capacities of the hMDPCs were not altered when expanded in media supplemented with PRP. All populations of hMDPCs that were expanded in PRP supplemented media retained their ability to regenerate myofibers in vivo. Our data demonstrated that PRP promoted the proliferation and maintained the multi-differentiation capacities of the hMDPCs during ex-vivo expansion by maintaining the cells in an undifferentiated state. Moreover, PDGF appears to be a key contributing factor to the beneficial effect that PRP has on the proliferation of hMDPCs.

Isolation of muscle-derived stem/progenitor cells based on adhesion characteristics to collagen-coated surfaces.

Our lab developed and optimized a method, known as the modified pre-plate technique, to isolate stem/progenitor cells from skeletal muscle. This method separates different populations of myogenic cells based on their propensity to adhere to a collagen I-coated surface. Based on their surface markers and stem-like properties, including self-renewal, multi-lineage differentiation, and ability to promote tissue regeneration, the last cell fraction or slowest to adhere to the collagen-coated surface (pre-plate 6; pp6) appears to be early, quiescent progenitor cells termed muscle-derived stem/progenitor cells (MDSPCs). The cell fractions preceding pp6 (pp1-5) are likely populations of more committed (differentiated) cells, including fibroblast- and myoblast-like cells. This technique may be used to isolate MDSPCs from skeletal muscle of humans or mice regardless of age, sex or disease state, although the yield of MDSPCs varies with age and health. MDSPCs can be used for regeneration of a variety of tissues including bone, articular cartilage, skeletal and cardiac muscle, and nerve. MDSPCs are currently being tested in clinical trials for treatment of urinary incontinence and myocardial infarction. MDSPCs from young mice have also been demonstrated to extend life span and healthspan in mouse models of accelerated aging through an apparent paracrine/endocrine mechanism. Here we detail methods for isolation and characterization of MDSPCs.

Fiber orientation and cell-cell coupling influence ventricular fibrillation dynamics.

Introduction: The structure of ventricular fibrillation (VF) is influenced by regional differences in action potential durations and perhaps restitution kinetics and fiber anisotropy. The spatial organization of VF was investigated by measuring the cross‐correlation (CC) and mutual information (MI) of membrane potential (Vm) oscillations recorded from multiple sites.

Biologic Strategies to Improve Nerve Regeneration after Peripheral Nerve Repair

BACKGROUND Peripheral nerve injuries remain a challenging problem for microsurgeons. Direct repair is the gold standard, but often the surgeon is left with a gap that prevents tension-free repair. The use of empty tubes/conduits/allograft has resulted in regeneration of some sensory and motor function, but the results remain suboptimal compared with autograft. However, the use of nerve autograft has associated donor site morbidity and limited availability. METHODS A review of the literature was performed to determine current biologic strategies to improve nerve regeneration after nerve repair. RESULTS Nerve conduits, various neurotrophic factors, and stem cells are currently being studied as alternatives to the use of nerve autograft. CONCLUSIONS Sensory and motor recovery after peripheral nerve regeneration remains suboptimal, especially in cases where primary nerve repair is not possible. Current strategies to augment nerve regeneration have focused on modulating the presence and activity of Schwann cells, either through direct implantation or by stimulating stem cells to differentiate toward Schwann cells, and through the use of neurotrophic factors to enhance the speed and quality of axon growth. Clinical studies will be necessary to determine the benefit of these strategies.

Venous Graft-Derived Cells Participate in Peripheral Nerve Regeneration

Background Based on growing evidence that some adult multipotent cells necessary for tissue regeneration reside in the walls of blood vessels and the clinical success of vein wrapping for functional repair of nerve damage, we hypothesized that the repair of nerves via vein wrapping is mediated by cells migrating from the implanted venous grafts into the nerve bundle. Methodology/Principal Findings To test the hypothesis, severed femoral nerves of rats were grafted with venous grafts from animals of the opposite sex. Nerve regeneration was impaired when decellularized or irradiated venous grafts were used in comparison to untreated grafts, supporting the involvement of venous graft-derived cells in peripheral nerve repair. Donor cells bearing Y chromosomes integrated into the area of the host injured nerve and participated in remyelination and nerve regeneration. The regenerated nerve exhibited proper axonal myelination, and expressed neuronal and glial cell markers. Conclusions/Significance These novel findings identify the mechanism by which vein wrapping promotes nerve regeneration.