Aging and Osteoarthritis (OA) related changes in joint tissues are in part due to an imbalance in expression of cartilage matrix genes and tissue degradation enzymes in chondrocytes. Elucidation of new molecules and mechanisms responsible for chondrocyte maintenance has potential to advance our understanding of OA pathogenesis and lead to new approaches to prevent or slow tissue damage. Krueppel-like factors (KLF) are transcription factors are involved in various biological and pathological mechanisms, including differentiation, apoptosis, cell reprogramming and tissue/organ homeostasis and protection against aging-related changes; however, their role in cartilage and joint homeostasis has not yet been examined. In preliminary studies we observed a profound reduction in the expression of several KLFs in human OA cartilage and in aged and OA-affected mouse joints. KLF overexpression or knock down in chondrocytes revealed KLF4 as a potent regulator of cartilage matrix genes Col2A1 and aggrecan. KLF4 also attenuated the IL-1 induced expression of catabolic factors These findings support the hypothesis that ‘Aging and OA-related reduction of KLF4 expression is a principal mechanism of tissue destruction and that restoring KLF4 protects against OA.’ Aim 1: Regulation of KLF expression and KLF function in chondrocytes: To investigate mechanisms of KLF4 suppression in OA, we will identify the role of cytokines/growth factors in regulating KLF4 expression. The role of KLF4 in regulating chondrocyte functions will be tested in cell and tissue culture models. Aim 2: The KLF4 signaling network in cartilage: Consequences of KLF4 suppression for signaling and gene expression networks are unknown in cartilage. We will use RNA-seq on cartilage from knock out mice, ChIP- seq and ChIP-seq for histone marks to identify KLF4-regulated target genes and signaling networks. Aim 3: Role of KLF4 in cartilage homeostasis, aging and experimental OA: We will delete KLF4 in mature mice using Acan-CreERT and examine mice for aging-related changes and severity of experimental OA. Aim 4: Protective effects of KLF4 overexpression and activation: Potential protective effects of KLF4 will be tested using novel transgenic mice that overexpress KLF4 in cartilage to balance the OA-associated KLF suppression and we will determine outcomes with respect to homeostasis mechanisms and OA severity. The potential impact of the proposed studies is that they will be the first to determine the role of KLF4 in cartilage homeostasis and the consequences of KLF4 suppression for joint aging and OA pathogenesis. We will also establish proof of concept for KLF4 as a therapeutic target in OA.