Inflammation and pyroptosis mediate muscle expansion in an IL-1{beta} -dependent manner [Molecular Bases of Disease]

January 16th, 2015 by Haldar, S., Dru, C., Choudhury, D., Mishra, R., Fernandez, A., Biondi, S., Liu, Z., Shimada, K., Arditi, M., Bhowmick, N.

Muscle inflammation is often associated with its expansion. Bladder smooth muscle inflammation induced cell death is accompanied by hyperplasia and hypertrophy, as the primary cause for poor bladder function. In mice, DNA damage initiated by chemotherapeutic drug cyclophosphamide, activated caspase 1 through the formation of the NLRP3 complex resulting in detrusor hyperplasia. Cyclophosphamide metabolite, acrolein, caused global DNA methylation and accumulation of DNA damage in a mouse model of bladder inflammation and in cultured bladder muscle cells. In correlation, global DNA methylation and NLRP3 expression was up regulated in human chronic bladder inflammatory tissues. The epigenetic silencing of DNA damage repair gene, Ogg1, could be reversed by the use of demethylating agents. In mice, demethylating agents reversed cyclophosphamide-induced bladder inflammation and detrusor expansion. The transgenic knockout of Ogg1 in as few as 10% of the detrusor cells tripled the proliferation of the remaining wild type counterparts in an in vitro coculture titration experiment. Antagonizing IL-1β with Anakinra, a rheumatoid arthritis therapeutic, prevented detrusor proliferation in conditioned media experiments as well as in a mouse model of bladder inflammation. Radiation treatment validated the role of DNA damage in the NLRP3-assocaited caspase 1-mediated IL-1β secretory phenotype. A protein array analysis identified IGF1 to be downstream of IL-1β signaling. IL-1β induced detrusor proliferation and hypertrophy could be reversed with the use of Anakinra as well as an IGF1 neutralizing antibody. IL-1β antagonists in current clinical practice can exploit the revealed mechanism for DNA damage mediated muscular expansion.