CAPM Part 1 and 2

Sir,
you said in your lecture of CAPM Part 1 that while measuring investor’s required return we consider only the systematic risks, as we assume the company specific risks have been taken care of by portfolio management.And beta is the measurement of the level of systematic risk of a company compared to the market which eventually determines investor’s required return.
On the other hand,gearing is a company specific risk.So, how can beta, a measurement of systematic risk which determines return, can be effected by gearing, which is a company specific risk.
If so, then this means, investor’s required return is indirectly effected by company specific risk, which doesn’t match with what you said earlier. I’m getting confused. Could you please make it clear to me?