Objective      To determine the effect of Ca2+/Calmodulin dependent kinase Ⅱδ (CaMKⅡδ) RNA interference on the gene expression of downstream genes and osteoclast differentiation in order to elucidate its role in the differentiation.   Methods      Lentivirus plasmids of recombinant CaMKⅡδRNA interference were constructed

and the best multiplicity of infection (MOI) value and transfection efficiency was determined. Mouse RAW264.7 cells were divided into 3 groups: control group

blank vector group and interference group. In 5 d after virus transfection

the cells were harvested and interference efficiency was determined. Then the effects of CaMKⅡδ RNA interference on the expression of nuclear factor of activated T cells type c1 (NFATc1)

tartrate-resistant acid phosphotase (TRAP) and non-receptor tyrosine kinase (also known as SRC proto-oncogene

c-Src)

and on osteoclast differentiation were determined.  Results      CaMKⅡδ RNA interference vector was constructed successfully

with the best MOI value of 30

and transfection efficiency up to 78% (P0.05). The interference efficiency was larger than 78% at mRNA level and 70% at protein level (P0.01). CaMKⅡδ RNA interference significantly decreased the gene expression levels of NFATc1

TRAP and c-Src by 47.8%

43.3% and 48.5% respectively at mRNA level (P0.01

P0.05)

and by 61.1%

48.2% and 39.6%

respectively at protein level (P0.01)

when compared with the other 2 groups. Immunofluorescent cytochemistry obtained similar results. CaMKⅡδ RNA interference also obviouisly decreased osteoclast formation and bone absorption. Compared with the other 2 groups

the number of osteoclasts

and the number and size of absorbed lacunae were reduced by more than 49.8%

47.6% and 61.3% respectively (P0.01) in the interference group.  Conclusion           CaMKⅡδ RNA interference significantly down-regulates the expression of NFATc1

TRAP and c-Src and inhibits osteoclast differentiation. CaMKⅡδ may play a key role in the process of osteoclast differentiation.