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Despite their paracrine activites, cardiomyogenic differentiation of bone marrow (BM)-derived mesenchymal stem cells (MSCs) is thought to contribute to cardiac regeneration. To systematically evaluate the role of differentiation in MSC-mediated cardiac regeneration, the cardiomyogenic differentiation potential of human MSCs (hMSCs) and murine MSCs (mMSCs) was investigated in vitro and in vivo by inducing cardiomyogenic and noncardiomyogenic differentiation. Untreated hMSCs showed upregulation of cardiac tropopin I, cardiac actin, and myosin light chain mRNA and protein, and treatment of hMSCs with various cardiomyogenic differentiation media led to an enhanced expression of cardiomyogenic genes and proteins; however, no functional cardiomyogenic differentiation of hMSCs was observed. Moreover, co-culturing of hMSCs with cardiomyocytes derived from murine pluripotent cells (mcP19) or with murine fetal cardiomyocytes (mfCMCs) did not result in functional cardiomyogenic differentiation of hMSCs. Despite direct contact to beating mfCMCs, hMSCs could be effectively differentiated into cells of only the adipogenic and osteogenic lineage. After intramyocardial transplantation into a mouse model of myocardial infarction, Sca-1 + mMSCs migrated to the infarcted area and survived at least 14 days but showed inconsistent evidence of functional cardiomyogenic differentiation. Neither in vitro treatment nor intramyocardial transplantation of MSCs reliably generated MSC-derived cardiomyocytes, indicating that functional cardiomyogenic differentiation of BM-derived MSCs is a rare event and, therefore, may not be the main contributor to cardiac regeneration.

Multiple sclerosis (MS) is a detrimental disease of the central nervous system (CNS) leading to long-term disability. In the course of animal models of multiple sclerosis (experimental autoimmune encephalomyelitis), we find enhanced activity of proteasome subunits b1i, b2, b2i and b5 in the CNS. We demonstrate that pharmacological inhibition of the proteasome by bortezomib ameliorates experimental autoimmune encephalomyelitis in mice and rats in prophylactic and therapeutic treatment with reduced numbers of T-cells secreting proinflammatory cytokines. The anti-inflammatory effect of proteasome inhibition was accompanied by reduced NF-jB activity in the CNS and lymphoid organs. The combined inhibition of proteasomes and lysosomal proteases involved in major histocompatibility complex II antigen presentation further improved therapeutic efficacy. We suggest proteasome inhibition alone or in combination with inhibition of lysosomal proteases as a novel therapeutic strategy against inflammation-induced neurodegeneration in the CNS. We demonstrate the impact of the proteasome and lysosomal proteases on development of autoimmunity.